[title]

TRANSACTIONS

OF THE

Royal Geological Society

OF

CORNWALL;

INSTITUTED FEBRUARY 11th, 1814.

VOLUME THE SECOND.

"A knowledge of our subterranean Wealth would be the means of furnishing greater opulence to the country, than the acquisition of the mines of Mexico and Peru."

President of the Board of Agriculture.

Demance:

PRINTED AND PUBLISHED BY T. VIGURS:

Sold in London by

BALDWIN AND CO.; LONGMAN AND CO.; AND WILLIAM PHILLIPS.

1822.

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V.—On the relative Age of the Veins of Cornwall.

By JOSEPH CARNE, ESQ. F.R.S., M.R.I.A.,
Hon. M.G.S.,

MEMBER OF THE SOCIETY.

(Read October, 1818.)

ALTHOUGH there is, perhaps, in no part of the world, a district of equal size, which can compare with Cornwall in the number and variety of its mineral veins, and the geological phenomena which attend them; most of the writers on this part of geology have, 'till lately, drawn their facts and illustrations from foreign countries. This is not at all surprizing; for it is but a few years since Britain has been roused to the pursuit of this science; and still fewer since Cornwall has attracted that degree of attention, either from strangers or from its own inhabitants, which is now so generally paid to it. Perhaps, however, few circumstances have occurred in relation to mineral veins,

G

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either in Hungary, Saxony, or Bohemia, which may not be observed in the veins of our own country.

The original formation of veins is a subject on which the two great parties which now compose the geological world, are almost as distant from each other as the surface of the earth is from its centre. It is, however, unnecessary to enter into their controversy at present. Circumstances relating to the Cornish veins will probably be adduced in the course of this paper, which may appear to favour the theory of each party. The singular situation, connexion, and appearance of the granite veins at St. Michael's Mount, and in some other parts of Cornwall, have been considered by the Huttonians as decisive proofs of the truth of their system: whilst the pebbles, or rounded fragments, in the metalliferous vein of the Relistian mine, have been regarded by the opposite party as unaccountable, on any other principles than those of the Wernerian theory.

The diversity of sentiment which exists with respect to the mode in which veins were originally formed, may possibly lead to a difference of opinion as to their positive age, or to the period or periods of their actual formation: but with regard to their comparative or relative age, I apprehend all parties (except those who hold that all veins are contemporaneous, and were formed

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at the same time as the containing rocks), are agreed on this important principle: that a vein which is intersected, or traversed, by another vein, is older than the vein by which it is traversed. This principle is slightly alluded to by Borlase, who quotes Hutchinson's authority for it:* but Pryce was, I believe, the first who plainly laid it down, in his Mineralogia Cornubiensis.† It is the principle on which Werner lays the greatest stress, in his New Theory of the formation of Veins:‡ and on the same principle, I would make a humble attempt to ascertain the relative age of the veins of Cornwall.

Veins have been divided into two general orders, viz: contemporaneous veins, or those which were formed at the same time as the containing rocks: and true veins, whose formation is supposed to be subsequent to that of the rocks which are contiguous to them.

By a true vein, I understand the mineral contents of a vertical, or inclined fissure, nearly straight, and of indefinite length and depth. These contents are generally, but not always, different from the strata, or the rocks, which the vein intersects. True veins have usually regular walls, § and sometimes a thin layer of clay

* Natural History of Cornwall, page 156.

† Page 101.

‡ Page 51, Anderson's Translation.

§ By this term is meant, that the rock of the country stands against the vein, on each side, as a wall, without being intermixed, or forming one body with it.

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between the wall and the vein: small branches are also frequently found to diverge from them, on both sides.

Contemporaneous veins have been usually distinguished from true veins by their shortness, crookedness, and irregularity of size, as well as by the similarity of the constituent parts of the substances which they contain, to those of the adjoining rocks, with which they are generally so closely connected, as to appear a part of the same mass. Two other marks, more distinctive, must be added. When these veins meet each other in a cross direction, they do not exhibit the heaves, or interruptions, of true veins, but usually unite. In a multitude of contemporaneous veins, some may appear to be heaved; but the apparent heave seldom affects more than one vein, and it is, in general, easy to perceive that what appear to be separate parts of the same vein, are different veins which terminate at or near the cross vein. When they meet with true veins they are always traversed by them.

With all these descriptive particulars, however, it is frequently very difficult to distinguish true from contemporaneous veins. There are few veins which can be brought to the test of all these marks; and there are probably exceptions to some of them. Some veins which are very short, are perhaps true veins; and others,

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of considerable length and width, and tolerably straight, may possibly be contemporaneous; but with respect to the latter, if the dip of the strata of the rocks in which they are found be minutely examined, it will probably appear that in most cases the inclination of those veins is parallel to it, and that they are therefore contemporaneous, rather as beds than as veins. Other veins there are, of such a dubious nature in many respects, as to render it necessary to place them in a separate order.

In examining, therefore, the veins which appear on the coast, and those which have been discovered in that small portion of Cornwall which has yet been penetrated by human industry and ingenuity, I shall, in the first place, attempt to distinguish those veins whose contemporaneous formation with the rocks which contain them appears the most probable. Those which are of a doubtful nature will form the second order: the third will comprize the various classes of true veins.

FIRST ORDER.—CONTEMPORANEOUS VEINS.

I. Granite Veins in Granite. These may be seen in several parts of the granite coast of Cornwall; particularly at the two promontories of Castle Treryn, on which stands the celebrated Logan-rock; and Tol Pedn Penwith, which

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is about a mile west of the former. They are of three kinds. Some are of considerable size, and their granite is of the same kind and colour as that of the rocks which adjoin them, but rather decomposed: they have no regular walls: several of them may be seen at Castle Treryn, and in the neighbouring rocks: one in particular, in a small cove west of the castle, about four feet wide, is visible from the top to the bottom of the cliff. There is another in the same cove, of much greater width, but not so distinct. A little further westward, another of these veins appears in a cavern, about four feet wide, with reddish felspar. Their direction is about north and south.*

There are other veins which only differ in colour from the granite which contains them: of these, a fine specimen is open to view on the eastern side of Tol Pedn Penwith: it is one foot in width, and its large crystals of felspar are of a beautiful red colour, whilst those of the adjoining granite are brownish white: it may be seen for about 40 feet in length.

The veins of the third description are composed of compact and fine grained granite, very different from the contiguous granite. These

* It is possible that most of these veins owe their appearance, as veins, to the percolation of water. The surface being lower than the adjoining country, the water has collected on it, and percolating through it in a perpendicular direction, has caused decomposition, and a consequent vein-like appearance.

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are numerous at Tol Pedn Penwith: they are from six inches to a foot in width, running in all directions: when they meet each other, they do not traverse, but unite, which is perhaps, one of the best proofs of their being contemporaneous.* Veins of this kind may be seen in other parts of the granite cliff between this headland and Castle Treryn.

Some of the veins termed by the miners Elvan-courses, (which will be presently described,) consist, when in a granite country, almost entirely of a fine grained granite; much finer than that of the adjoining granite, although composed of nearly the same constituent parts. They may therefore be denominated granite veins, although they probably belong to the elvan formation. The elvan-course of Rose-wall-hill tin mine, near St. Ives; and another, situated a little to the west of Huel Damsel copper mine, are of this description. At Cligga Point also, there is a large course, or body, of granite, which may possibly belong to the elvan formation.†

II. Veins of Felspar. These also may be found in several parts of the granite coast, particularly in the rocks westward of Castle Treryn. They have no walls, and although one of them

*Some of those veins are so straight and regular, they have walls so distinct, and are so easily separated from the containing rocks, that I think they are true veins, and posterior to the others.

† See "Elvan-courses" in the next order of veins.

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is nearly a foot in width, they are generally very small, short, and tortuous. The felspar is very compact, and the veins may be easily distinguished by their bright red colour.

III. Veins of Mica. These have hitherto been found only in the granite of St. Michael's Mount. They are seldom more than half an inch wide; and although tolerably straight, are very short. They generally consist of two layers of mica in plates, which meet in the centre of the veins.

IV. Veins of Shorl. These have been found in both granite and slate.* In the former, at Castle Treryn and the neighbouring rocks, where they are seldom more than an inch wide, and are tolerably straight, but short. They occur in slate at Botallack mine, in St. Just, particularly on the crown rock, where they vary in size from an inch to above a foot: of some the

* In the central mining district of Cornwall, the stratified rocks are, in general, composed of argillaceous shistns, or clay-slate. On some parts of the coast, especially the south-western coast, these are frequently mixed with compact hornblende rocks, with which they often alternate. In the western part of St. Just, the rocks which overlie the granite are mostly composed of compact and slaty hornblende rock, which has been of late commonly denominated greenstone, although in much of it there is little appearance of felspar. The slaty rock rather merits the name of hornblende-slate. As, from the situation of all these rocks, there is good reason to suppose they belong to the same formation, I shall, in this paper, use the term slate for the whole.
The clay -slate is, in many parts, overlaid by greenstone, particularly near Cuddan-point, in Mountsbay, where the slate dips towards the south: the junction here is more distinct than I have seen it any where else in Cornwall.

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inclination is parallel to the dip of the slate; but of others it is different.

In a part of Botallack, called the Bunny, at the junction of the granite and slate, are some large bodies of tourmaline, called by the miners "floors of cockle:" these cannot be denominated veins, and the relative period of their formation is doubtful, as they occur between the two rocks, and tin has been found under them.

V. Veins of Shorl-rock. I should have made no distinction between shorl and shorl-rock, had not the latter obtained a separate place in Jameson's classification of rocks. The contemporaneous veins of this rock are found only in granite: one of them, at Castle Treryn, is nearly two feet wide: it has no distinct walls, is highly inclined, and very short: they may, however, be seen on a larger scale in the rocks near Rosemodris, about five miles south-west from Penzance, near the junction of the granite and slate; some of them are two feet wide, and may be seen crossing the granite rock for at least 100 yards in length, but they do not enter the slate: when they meet each other, they usually unite. The veins of shorl-rock which occur in the slate, as at Zennor, appear to be true veins, as there is a perfect line of separation between the veins and the slate, and they invariably traverse the granite veins which appear on that coast.

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VI. Veins of Quarts. I include in this class only the small quartz veins which, in almost all the western part of Cornwall, intersect the slate, the greenstone, the greywacke, and the granite, in all directions; the slate and the grey wacke more generally than the others. Most of these veins have no distinct walls, and are irregular in size, direction, and inclination. They are intersected by all true veins, and frequently, when in slate, by the granite veins, as at Mousehole, and St. Michael's Mount. When two or more of those veins meet, they generally unite, and shew no kind of interruption.* On those parts of the coast where the slate and the granite meet, the same contemporaneous quartz veins rarely, if ever, appear in both rocks; but usually end with one of them.

VII. Veins of Actynolite and Thallite. These occur in the slate rocks on several parts of the coast of St. Just, between Cape Cornwall and Pendeen Cove:† also, in the slate rocks between Penzance and Chyandour. In the Greeb,

* In some instances, one of those veins appears to be heaved by another. It is probable however, as has been already observed, that what appear to be opposite parts of the same vein, are the terminations of different veins.

† At Cape Cornwall those veins are from two to eight inches wide. At Botallack, there is a vein of thallite, distinctly crystallized, about six inches wide, on the crown-rock, but in a part very difficult of access.

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an insulated slate rock near St. Michael's Mount;* and in the greenstone cliffs near Cuddan-point.

The veins of Actynolite are, in general, very short, and are neither straight, nor regular. They may probably be found in the slate rocks on many other parts of the coast of Cornwall. I have never observed them in granite. A small vein of decomposing actynolite crosses a large vein of axinite, in the rocks near Huel Cock, in St. Just.

VIII. Veins of Axinite. There are some veins of this mineral in the greenstone rocks at Cuddan-point; but the principal veins are in St. Just: the largest which I have seen, occurs in the cliff near Huel Cock: it is three feet wide, and may be seen for perhaps twenty yards in length. In this vein have been found specimens which may vie with those of Dauphiny. Its direction is about north-east and south-west, and it underlies rapidly towards the south-east. This is the only vein of which the axinite has a violet colour. Several smaller veins may be seen in the same rocks, and also in the rocks between Huel Cock and Botallack: these however are, in general, very short and tortuous. In the crown-rock, there appear, at first sight, numerous veins of this mineral, from a quarter of an inch to an inch

* In the Greeb is a vein of asbestus-actynolite, mixed with axinite, from four to twelve inches wide.

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in width, inclining towards the west; but on examination, it will be found that their inclination is at the same angle as the dip of the strata of the rock: they must therefore be considered as beds.

IX. Veins of Garnet-rock. One of these occurs in the crown-rock at Botallack, which consists almost wholly of garnet, and abounds in irregular crystals of that mineral. In one part it is almost a foot in width: it runs nearly north and south, but is very short. The crown-rock, which contains it, appears to be composed of slate, greenstone, garnet-rock, shorl, axinite, and many other minerals. Another large vein of garnet-rock occurs in the slate rocks of Huel Cock Carn, adjoining the large vein of axinite: its direction and underlie are the same as those of that vein, but it is very short. Other veins may be seen near a rocky headland called Cam Boscawen.

X. Veins of Prehnite. The only spot in Cornwall where these have yet been found, is between Botallack and Huel Cock, in the slate rocks. They are very irregular, both in size and direction: I have not seen more than two of them, the largest of which is from two to six inches wide: the inclination of one of them is very great, and is nearly the same as the dip of the strata; but that of the other appears dif-

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ferent. Asbestus and stilbite have been found in the veins, with the prehnite.

XI. Veins of Chlorite. The chloritic slate of the Relistian Mine, in Gwinear, contains numerous minute and short veins of chlorite, which, although they occur in the neighbourhood of a chlorite tin lode, yet, from their situation and position, they can only be regarded as contemporaneous. I have also observed veins of foliated chlorite, in the chlorite of the tin lode. Veins of chlorite also occur in greenstone at the Wherry tin mine.

XII. Veins of Iron-stone or Ire-stone. This stone, to which the name of Iron-stone has been given on account of its extreme hardness, appears to consist, principally, of very compact hornblende, with chlorite and quartz. Few veins of this stone have yet been discovered, much to the satisfaction of the miner, to whom they are, above all things, the objects of hatred. They are generally very large, and run nearly east and west. The principal of those veins is about 20 fathoms wide, and is supposed to extend several miles in length, eastward from Roskeere, in Camborne. Another vein of it has been found in Tincroft mine, about the same width; and a third, about ten fathoms wide, a little to the south of Huel Neptune: the latter becomes much wider as it extends eastward. These veins are highly inclined, especially the

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last mentioned; but whether their inclination is the same as that of the adjoining strata, has not been ascertained. They are all in slate, in which also are sometimes found detached masses of iron-stone. Very little is known respecting these veins, nor is our knowledge likely to be increased.

XIII. Veins of Serpentine. I have observed veins of this mineral crossing the green-stone at Porthallow, in St. Keverne, in all directions: and it is singular that, although the veins of serpentine enclose minute veins of steatite, the latter seldom appear in the greenstone. In many parts of the serpentine district near the Lizard, it is common to observe veins of one colour crossing a mass of a different colour. At Pradannack, a mass of blueish-green serpentine abounds in veins of a bright red colour At Gew Grease, where the soap rock occurs, there are veins of a greenish colour crossing the other serpentine. These veins are generally very short and tortuous.

XIV. Veins of Greenstone. The greeny-stone of St. Keverne contains veins of the same mineral, some of which are more compact than the containing rock, and others less so. Veins of greenstone may also be found in the serpentine on Goonhilly downs. They are generally very small and short, and are too closely con-

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nected with the rocks in which they are found, to allow the idea of their being true veins.

XV. Veins of Asbestus. These may be seen in almost all the serpentine formation of the Lizard: some of them are as wide as half an inch; but their width, in general, is that of a line, running in all directions. At Gew Grease some veins may be seen upwards of an inch Wide. The principal veins, however, occur at Kennack Cove, about three miles north-east of the Lizard, in greenstone: here there are some so wide as three to four inches: their position is sometimes quite horizontal. Veins of asbestus occur also in the greenstone, and serpentine of Clicker-tor near Liskeard.

XVI. Veins of Agate. I believe the only spot where these are to be met with, is between Kynance Cove and the Lizard, in the serpentine, near its junction with the clay-slate. They are very minute and irregular. They were discovered by Mr. Majendie, who has noticed them in his paper on the geology of the Lizard.

XVII. Veins of Calcareous Spar in Limestone. These occur in slaty limestone at Crantock, and near Padstow; and in transition limestone in the parishes of Veryan, South Petherwin, Menheniot, Warleggan, and Newport; and also on the northern side of Mount Edgcumbe. I believe the contemporaneous formation of such veins

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has not often been doubted. They are so common wherever transition limestone occurs, that a particular description of them is unnecessary.

The veins which have been hitherto described (with the exception of those of chlorite and iron-stone) may all be denominated rock-veins. There are however, other veins which appear under different circumstances, and must not pass unnoticed. These may be styled veins within veins, as they are found only in the veinstones of other veins. They are probably contemporaneous with those parts of the other veins in which they are found, although perhaps not always so with the rocks which contain those veins.

XVIII. Veins of Jasper. I believe this mineral has hitherto been found in Cornwall, only as a constituent part of some lodes, or metalliferous veins. It has thus been found in the tin and copper lode at Botallack, where veins of yellow and greenish jasper are frequently seen crossing the coarse red jasper. In Huel Stennack, and Huel London, (both in St. Just,) veins of red jasper often appear in the quartz and the mixed stone of the tin-lodes, but are seldom larger than a quarter of an inch. In the lode of Ding Dong tin mine, minute veins of red and black jasper in quartz, are not uncommon. All these veins are very short, and appear in all directions and positions.

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XIX. Veins of Opal. I have observed these only in one part of St. Just, viz. in the old heaps of Huel Stennack and Huel London. They occur in the dark quartz of the tin lodes, and are in general very minute and short. Some of the opal is of the kind which is known by the name of fire-opal, and is of a blackish yellow colour. The lodes which contain the veins of opal and jasper are in granite.

XX. Veins of Fluor-spar. This mineral has occurred in Cornwall only as a veinstone of the metalliferous veins, and is commonly of a white or green colour: but in one of the lodes of Botallack, it has been found very similar to the fluor of Derbyshire, having purple veins of the same substance running through it in all directions.

Those are all the reins which I have yet met with, of whose contemporaneous formation there is the greatest probability: a further and more minute examination will perhaps bring others to light. But although they may all be contemporaneous with the rocks which contain them; it does not follow that they are all of the same age: on the contrary, as some are found in granite; others in slate; others in greywacke; others in serpentine; and others in limestone; their ages must be as different as those of the containing rocks.

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SECOND ORDER.—DOUBTFUL VEINS.

This order will comprehend all the veins, whose situation, appearance, and attendant circumstances, render it doubtful whether their formation was contemporaneous with, or posterior to, that of the rocks which contain them. In this order may be classed,

I. Granite veins in Slate. These have been discovered in no less than fourteen places on the coast of the western part of Cornwall, between Porthleven and St. Ives Head, viz. (beginning at the most eastern point.)

1. About half a mile eastward of Trewavas Head, in the parish of Breage.*

2. On the eastern side of Portcue Cove, in the same parish.

* Those veins are the most gigantic, as well as the most distinct, and regular, of any in Cornwall. Their edges appear in the perpendicular cliff; and being very white, and the slate very dark, the contrast is striking. They are all highly inclined: the three largest are eight feet wide: their direction is nearly north and south, and they underlie rapidly towards the east: their edges may be seen on the underlie, for 150 yards: in the upper part, some of them become united, and appear to join a mass of granite, about 40 feet thick, which reposes horizontally on the slate. This mass has been considered by some geologists as the result of the union of several granite veins, and therefore as belonging to the same formation as the veins; The union of the veins with the mass has not, however, been ascertained, although it is very probable; for at the point of junction, the rocks are inaccessible, and are covered with weeds and muddy sediment. The slate strata are horizontal: the veins therefore interrupt them; but they come nearer to the lines of the slate than any others I have observed. One of them contains fragments of slate, and they all contain a very large proportion of quartz, with scarcely any mica.

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3. On the western side of the same Cove.*

4. At St. Michael's Mount.

5. At the village of Mousehole.

6. At Rosemodris, three miles south-west of Mousehole.†

7. At Cam Silver, about half-a-mile west of Rosemodris.‡

8. Near Whitesand-bay, between the Land's-end and St. Just.

9. At Porth Just, joining Cape Cornwall on the south.§

10. At Polladan Cove, joining the same Cape on the north.

* At the most western point of this cove, the slate, instead of being closely united to the granite, appears as if it were simply and loosely laid upon it.

† At this spot the slate which adjoined one of the granite veins is fallen off from one side of it, for several yards in length, and has left it completely exposed.

‡ Here the slate, which occupies about half a mile of the coast, appears to fill a granite basin; for at the eastern point, the granite underlies to the west at an angle of 26 degrees; and at the western point it underlies to the east at an angle of 60 degrees from the perpendicular. On this spot there is an instance of a granite vein penetrating the main body of granite. A small mass of slate incumbent on the granite, has a granite vein, about four inches wide, running through it; and on each side of it, the vein may be traced for several yards in the granite: on the eastern side, at a little distance from the slate, it has the appearance of a vein of shorl-rock: this will shew the near connexion which subsists between shorl-rock and granite.

§ Here, and at Polladan Cove, the granite, in several parts, appears insulated in the slate; but from the relative situation, and size of those apparent bunches, they probably belong to different veins, whose continuity, at the surface, has been either prevented, or broken, by the slate. The large vein at Porth Just, six feet wide, appears to me to be, not a granite vein, but an elvan course.

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11. At Chycornish Carn, near Botallack,

12. At Pendeen Cove, in St. Just.

13. At Polmear Cove, in Zennor.*

14. At the Cove north of Zennor church.

As the veins in several of these places have been described in the first volume of the Transactions, I shall only give, in notes, a few particulars of those which are most remarkable and which have not been already noticed.

The relative age of those veins has been a subject of as much discussion as almost any point in geology; especially as it appears to involve several other points, which are deemed, by different parties, of essential consequence to their systems. I believe the more they are examined, the more difficult it will be found to form any consistent theory respecting them: in order, however, to be convinced of this, it is necessary to examine them at every place where they have been discovered; for so different are their appearance, and attendant circumstances, in different parts, that a very plausible theory made with reference to the veins of one spot

* These veins are as singular, and as interesting, as any in Cornwall. They are from the smallest possible width to nearly two feet: they run in several directions: some of them are vertical; others are inclined at different angles, and some are completely horizontal. In one part of the cove, where one of the veins inclines at an angle of full 45 degrees, the slate is fallen from the upper side, and has left a part of the veine xposed to view. Near the same spot is an apparent inter-section of one granite vein by another, each of which is about a foot wide. One of them appears to be heaved five feet to the left.

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only, will be found quite inconsistent with those of another. From the whole, however, the following facts may be collected.

1. They occur only at, or near, the junction of the granite and slate.

2. They are not metalliferous.

3. They have no general direction or position. At Mousehole, and Polladan Cove, they run east and west: those at St. Michael's Mount,* and some at Porth Just, run W. N. W. and E. S. E.: those at Polmear Cove, north and south. Some are quite vertical, as at Portcue, Rosemodris, and Polmear Cove: those at St. Michael's Mount and Mousehole are nearly so: others are inclined at different angles, as at Trewavas Head, Porth Just, and Chycornish Carn; and others quite horizontal, as at Polmear Cove: at the latter place, indeed, they may be seen in almost all positions.

4. Their direction is usually as straight, and their size as regular, as those of true veins; but in some cases they become smaller as their distance from the granite mass increases.

5. Their greatest length has never been ascertained: some at Rosemodris may be traced

* Dr. Berger asserts (Geol. Trans. Vol. 1. page 146.) that the granite veins are invariably directed from north to south: surely this was a slip of his pen, as the veins at the Mount, which was the principal object of his attention, must have convinced him of the contrary. These veins are from half an inch to a foot wide, and underlie a little towards the north.

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in the slate nearly 200 feet, and are then lost in the sea.

6. The granite of the veins generally appears different from that of the main body; it is of much smaller grain: it contains a much larger proportion of quartz, and very little mica: sometimes indeed, no mica at all.

7. The slate which is contiguous to the veins becomes almost imperceptibly changed from clay-slate to mica-slate, and sometimes has even the appearance of gneiss.

8. The slate which is close to the veins, is frequently much harder than that which is more distant from them, and its texture is, in general, not so slaty.

9. At St. Michael's Mount, and Polmear Cove, the veins may be traced to the granite mass, with which they appear to be in complete union, and to form one body, losing entirely their character as veins. Whether the other veins unite with the granite mass or not, has not been ascertained, as the point of junction is seldom accessible, or even visible.

10. At Carn Silver, one of the veins may be traced from the slate into the granite mass. This is the only instance which I have discovered of a granite vein penetrating both the slate and the granite.

11. Some veins (as at Carn Silver, Chycornish Carn, and Pendeen Cove,) are closely

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connected with the slate, and the two bodies appear intimately united, and inseparable. In fact they appear contemporaneous. Others (as at Trewavas Head, the western side of Portcue Cove, Rosemodris, and Polmear Cove,) are so easily separable from the slate, and have walls so distinct, that, under any other circumstances, they would be taken without hesitation for true veins.

12. Fragments of slate are visible in several of the veins, as at Trewavas Head, St. Michael's Mount, Mousehole, Porth Just, &c. I have not observed them in the main body of granite.

13. At Mousehole, and at St. Michael's Mount, the slate is intersected by numerous small quartz veins, some of which are traversed by the granite veins: others, on the contrary, traverse and heave both the granite veins, and the other quartz veins.*

14. At Mousehole, and Whitesand-bay, where a junction of the main bodies of granite and slate takes place, they appear, at some points, so completely intermixed, as almost to exclude any other idea than that of contemporaneous formation, although, at other points, the junction is distinct and regular.

* At Mousehole, one of the granite veins is heaved three feet to the left, by a quartz vein, in which slate is mixed with the quarts. By another, two granite veins are heaved to the left: one nearly three feet; the other, six inches: the two latter heaves occur nearly at low water mark.

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15. In most other places where the junction occurs, the slate reposes on the granite, without any appearance of a dislocation, or disturbance of the strata: particularly at Portcue Cove, Carn Silver, and Polmear Cove.

Now from these facts, taken separately, very different conclusions might be, and have been, drawn.

From the union of some of the veins with the granite mass at St. Michael's Mount, and at Polmear Cove, it has been concluded that the veins and the mass are contemporaneous: if so, was the whole formed before, or after the slate? Before; says Dr. Berger; who, on Viewing the veins at Mousehole, and at St. Michael's Mount, which are nearly vertical, concludes that they were ridges protuberating from the mass of granite, the spaces between which were afterwards filled with the slate: had he, however, seen the horizontal veins at Polmear Cove, and the highly inclined veins near Trewavas Head, he would have found them decidedly opposed to such a conclusion.

Dr. Thomson and Mr. Allan, on the contrary, (from an examination of St. Michael's Mount,) unite in the supposition, that both the veins and the mass are posterior to the slate, although they widely differ in opinion as to the mode of their formation. The former thinks that the

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whole is transition granite.* The latter contends that both the mass and the veins were thrown up from beneath. In the former case, the whole of the granite must have been deposited on the slate. In the latter, could it possibly have been thrown up from below the slate in a fluid state, and yet not have run over any part of it? and would not the fragments of slate be as common in the mass as in the veins? I apprehend, however, that in no part of St. Michael's Mount is the slate to be found under the granite.†

From the intimate union which subsists between some of the granite veins and the slate

* (Annals, vol. 2, page 253.) As there is not a single visible point of junction of the granite and slate on all the coast of Cornwall, where there are not granite veins intersecting the slate; we may fairly conclude on the existence of similar veins at those points of junction which are hidden from our view. If Dr. Thomson's inference, there-fore, be correct, that the granite veins at the Mount, prove the whole granite mass to be transition granite, and posterior, in point of formation, to the slate; it will equally apply to all the granite of Cornwall: or at least to all those parts where the veins are in union with the main body of granite. If this, however, were the case, should we not long since have discovered, in our deep mines, other rocks under the granite?

† Dr. Thomson says that on the west side of the Mount, there are two beds of granite in the slate, in such a position as to prove that the great body of granite was deposited after the slate. It does not appear to me that those granitic bodies can, with any propriety, be called " beds in the slate." One of them is a granite vein, and although six feet wide near the granite mass, it becomes gradually smaller as it recedes, and dwindles to a point at the distance of 80 feet. The other is a part of the granite mass, from which some veins appear to diverge, and in no part does it overlie the slate.

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which contains them, it has been contended By other geologists, that the veins and the slate are contemporaneous: To this, some would reply by asking, how came the fragments of slate into the veins? and how could some of the quartz veins in the slate be traversed by the granite veins?

Others have cut the knot which they have found so difficult to untie, and declared the whole mass, consisting of the main bodies of granite and slate, the granite veins, and all the other veins which appear in the mass, to be contemporaneous.

Others, however, have come to a different conclusion. They argue, 1. from the fact of some of the granite veins traversing the contemporaneous quartz veins; and 2. from the fragments of slate which are frequently found in them; that the granite veins are of a more recent formation than the slate which contains them. They also contend, 1. from the granite of the veins being generally different, in many respects, from that of the mass; 2. from the fragments of slate not being found in the mass as well as in the veins; and 3. from the slate being rarely, if ever, overlaid by any part of the granite mass;* that the main body of granite may

* Instances of granite fairly overlying the slate (except in the case of the granite veins) are very rare in Cornwall. The mass reposing on the slate near Trewavas Head, is the most conclusive; but even that has been disputed. The granite at Cligga Point (if it is not a large elvan course,) might be called secondary or transition granite, without affecting the age of the granite of other parts of Cornwall, as it is far from the large granite chain: The apparent alternations of granite and slate at Dolcoath, Cook's Kitchen, and Tincroft, may be caused either by the occurrence of highly inclined granite veins, or by the slate filling up the irregularities in the granite. What has been called granite at Huel Fortune is evidently an elvan course. But even were this alternation more general, it would only prove that in Cornwall, as in other countries, two primitive rocks, at, or near, the point of their junction, sometimes alternate with each other: and does not this render it probable that although, in strictness, the main body of the one may be said to be anterior to that of the other, the formation of the former was scarcely finished when that of the latter began? How else can we account for the fact, that the extremities of the granite and clay-slate exhibit a change in some of their qualities, almost wherever a junction occurs? In this view, the extremities of the two bodies may be said to be contemporaneous. In the present case, the body of slate which is intersected by the granite veins is so comparatively small, that we may perhaps form an idea of the formation of the surface of the granite mass, the thin body of slate, and the granite veins, following so closely on each other, as to render the whole, as nearly as possible, contemporaneous: the union of the veins and the mass might thus have been easily formed.

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have preceded the slate, although the granite veins (as veins) may have followed it.

If the whole of the veins which have been described were subject to one general conclusion, the last would, perhaps, appear the most reasonable; but the circumstances in which they are found are so diverse, that it is possible they may not all bear the same relation to the containing rocks; and that their formation may have taken place in different modes, and at different periods.

There are several mines in Cornwall in which the slate (killas) and the granite meet. In some

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of these, viz. Huel Unity, Huel Gorland,* Treskerby, Tincroft, Cook's Kitchen, Dolcoath, and in some of the St. Just mines, the lode (or metalliferous vein), when near the point of junction, has one of its walls of slate, and the other of granite. In some cases, this is probably owing to the occurrence of granite veins in those mines, a granite vein being one of the walls of the lode.

From the occurrence of granite veins in the slate, wherever the junction of the two rocks has been discovered on the coast, and from their probable existence in the mines in which both the rocks occur; it is very likely that if the lines of their junction throughout Cornwall could possibly be laid open to view, granite veins would be seen traversing the slate, at almost every point.

II. Veins of Steatite. These are very plentiful in the serpentine of the Lizard, particularly in the parish of Mullion. Near the village of Pradannack is a vein from one to two feet wide:

* Dr. Berger (Geol. Trans. vol. 1. page 146.) says there are granite veins called lodes by the miners, running north and south, in Huel Gorland and Dolcoath. I cannot find that such is the fact. Indeed I am not aware of a single metalliferous granite vein in the whole of Cornwall. There are lodes in Huel Damsel, Huel Jewel, Huel Virgin, and in some mines in St. Just, in which granite is occasionally found in bunches; but these are all in a granite country. I have seen the red oxide of copper in granite from Huel Damsel, and the oxide of tin from St. Just, but the granite was either from the walls, or from occasional bunches in the lodes. I do not recollect an instance of a metalliferous vein being traversed by a granite vein.

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their principal locality, however, is Gew Grease, better known by the name of the Soapy Rock, where they are from six inches to three feet wide, running north-east and south-west, and underlying towards the south-east. On following some of the veins upwards, the back, or top, will be found to consist almost wholly of quartz. Other veins occur at Pentreath, between Gew Grease and the Lizard, and also near the village of Cadgewith; but they are seldom larger than a few inches. Their colour varies from white to yellow, green, and purple. The veins of steatite have distinct walls, and are as regular as most true veins. Fragments of serpentine and calcareous spar are sometimes found in them. I consider them, therefore, as true veins; but I have placed them in the doubtful order, because some geologists, whose judgment is entitled to respect, are of a contrary opinion. Dr. Berger thinks that steatite bears the same relation to serpentine, as kaolin does to granite:* and Dr. Thomson supposes the steatite is a portion of the serpentine, altered by the action of water, or some other cause.† Sir H. Davy, however, considers those veins as mechanical deposits.‡

I have lately observed veins of white steatite in the slate rocks at Pendeen Cove, in St. Just.§

* Geol. Trans. vol. 1. page 131.

† Annals, vol. 2. page 251.

‡ Cornw. Geol. Trans. vol. 1. page 143.

§ The rocks in this Cove have more of the nature of clay-slate, than any others in St. Just.

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These also, although most of them are very small, want that close connection with the containing rocks, which is generally essential to contemporaneous veins.

III. Veins of Calcareous Spar. The veins of this mineral which have been already described (in limestone), will probably be easily admitted into the contemporaneous order. Those which occur in other rocks are more doubtful. 1. In serpentine: these may be seen principally at Gew Grease, and at the junction of the slate and serpentine near the Lizard Point: they are in general small; some are short and tortuous, but others are straight and regular, and have distinct walls: the carbonat of lime, which is frequently fibrous, is easily separated from the rock. 2. In slate: the rocks, on the coast of St. Just, from Cape Cornwall to Pendeen, contain numerous veins of this mineral, in which it occurs both massive, and crystallized in different forms; although they are small and short, they are in general tolerably straight, and have regular walls. 3. In the Greywacke, near Padstow, veins of calcareous spar are visible, very similar to those which occur in the serpentine.

IV. Elvan Courses. From the great width of many of these, they are termed by the miners channels, or courses, rather than veins. They are generally composed of a mixture of horn-

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stone, quartz, and felspar; having the appearance of hornstone porphyry. Other substances, however, are called elvan by the miners: thus; a stone composed of very compact hornblende and chlorite is called blue elvan in Huel Ann: a mixture of hard hornblende and quartz has the same name at Botallack: a compound of felspar and hornblende is elvan at Gwallan, and is as soft as the neighbouring country: a mixture of hornstone, quartz, shorl, and chlorite, forms the black elvan of Chasewater; and it has been already mentioned that fine grained granite is the elvan of Rosewall-hill. Hardness is not an essential quality of elvan.

In Chasewater copper mine, and in the Wherry tin mine, elvan may almost be called a veinstone, as small veins of copper and tin proceeding from the lodes, are frequently found in the elvan courses. In the Wherry, it had the name of " stannified porphyry." In a part of Huel Unity, the elvan is so rich in tin, that it is considered as the tin lode.

The elvan courses vary in width from one to sixty fathoms, or 360 feet.* Their direction is generally a little north of east, and south of west,† and they almost always underlie to-

* The elvan course in Huel Alfred is in some parts 60 fathoms wide, but in general not more than 50.

† I have heard of very few which have a different direction. There is one in Ting-tang copper mine, another in Huel Fortune tin mine, and a third in Ludgvan, which run south of east and north of west.

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wards the north: perhaps on an average, a foot to every foot in depth, or at an angle of 45°.* The extent of their length has never been ascertained, although one of them has been traced five miles. They furnish most of the building stone of the neighbourhood.

The elvan courses of Cornwall are generally called by geologists, porphyry dykes; but there is an essential difference between them and the dykes of the north of England. The latter intersect, and frequently heave, both the lead lodes and the coal strata; but the elvan courses intersect no true veins.†

Elvan courses may be seen at the surface almost wherever a quarry of building stone is opened in a slate country; but the spot where they may be viewed most advantageously, is the cliff between Trevellas Head and Cligga Point, in St. Agnes: there are there four elvan courses, all open to the day, to the extent of their whole width, and for a considerable length: the first, which may be seen from Trevellas Head, overlies a part of the slate cliff: the three next form a considerable part of Cligga Head-land. Beyond these is the mass which forms Cligga Point,

* I know only two or three which underlie towards the south. In the Wherry tin mine, formerly wrought under the sea near Penzance, the underlie is, in some parts, two fathoms, to one in depth: an underlie so great, that the workmen would actually walk up its southern wall.

† One instance to the contrary has been discovered in Polgooth, which will be presently noticed.

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and which is, probably, from 150 to 200 fathoms in width, overlying the slate. On the surface, and for a considerable way down the cliff, it appears to be decided granite; but in the lower part of the cliff it assumes an elvan appearance. It has, therefore, been called by some, a secondary formation of granite, and by others, a part of a granitic elvan course.* This mass, when viewed at a small distance, appears to be obliquely stratified; but on a nearer approach, the dark lines which appeared like breaches between the strata, are found to be small veins of blackish quartz, whose contemporaneous formation can scarcely be doubted. Many of those veins contain tin, and the numerous holes made by the miners in different parts of the rock, in order to get at the tin, together with the large and sharp ridges which have been made by taking away the veins, give the whole, when viewed from the bottom of the cliff, a most romantic, as well as terrific appearance.

Elvan courses have been considered as contemporaneous with their enclosing rocks, because they are traversed by metalliferous and other veins, in nearly the same manner as the

* It is not improbable that all those elvan courses become united between Cligga Point and the headland north of St. Agnes pier, and afterwards assume a more westerly direction, as, in the cliff near the old tin mine of Polberrow, a large granitie elvan course is visible, which has been traced as far west as Huel Coates, where it is quite decomposed, and contains so much felspar, that a large quantity of china clay has been extracted from it.

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slate and the granite: this, however, only proves their priority to those veins. It has also been alleged that elvan has been found in floors, as in Crenver and Penberthy-Crofts mines; and in bunches, as in the United mines, and Huel Squire, which are all in slate. It is probable, however, that what the miners calf floors, are elvan courses, greatly inclined; and it is questionable whether, if the bunches were traced, they would not be found connected with neighbouring courses. I have never heard of bunches of elvan, except in the neighbourhood of elvan courses.

It must be observed on the other hand, in favour of their posterior formation, 1. that they do not always underlie in the same direction, and scarcely ever at the same angle, as the dip of the slate.* 2. Some elvan courses have been discovered partly in slate, and partly in granite, as in the copper mines of Tresavean and Treskirby.† 3. Fragments of slate are found in elvan courses close to their walls, or their junction with the slate country. 4. The elvan

* The elvan course of the Wherry mine underlies north, whilst the slate dips south-east. This course may be distinctly seen at low water, just behind Penzance pier, and it is what Dr. Thomson alludes to, when he says " Beds of a granitic rock are seen rising out of the sea just behind this pier." (Annals, Vol. 2. page 347.) The elvan courses at Cligga all underlie northwards, but the slate dips rapidly towards the south.

† The elvan courses in those mines are harder when in the granite, than when in the slate.

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course in Polgooth tin-mine traverses and heaves all the veins which it meets with, except a flukan vein, by which it is itself heaved.*

These are all the circumstances which occur to me, either in favour of, or against, the contemporaneous formation of elvan courses. The result of the whole appears strongly in favour of their being true veins, of which they probably form one of the earliest classes.†

Tin lodes are, in general, richer or poorer in the elvan, than in the slate, in proportion to the hardness or softness of the elvan. In Rosewall- Hill, where the elvan was hard, the lode became poor; but in Huel Vor, where it was soft, the lode improved. Copper lodes are generally as rich, and frequently richer in the elvan, than in the slate, or the granite; as at Treskirby, Huel Alfred, and Nangiles. At Tingtang, the lodes are richest when they are between the slate and the elvan.

V. Veins of Oxide of Tin. I have considerable hesitation in placing any of the metalliferous veins in the contemporaneous order: yet there are some which present a very doubt-

* This elvan course may be more recent than the other veins, but as it is a solitary instance, it cannot affect the age of other elvan courses. See a paper by John Hawkins, Esq. in Vol. 1. page 143, on the Lodes of Polgooth.

† In my paper on Elvan courses, in Vol. 1. I supposed them to be of the same age as the adjoining rocks. I have here inclined to a different opinion, and have stated the grounds of it.

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ful appearance. The greatest part of the veins which contain this mineral are evidently true veins; but it is probable that some of the smaller contemporaneous veins of quartz are metalliferous, and contain the oxide of tin, as at St. Michael's Mount, and Cligga Point. The veins, however, to which I particularly allude, are situated in the Sealhole mine, in St Agnes, and are composed entirely of oxide of tin. They are extremely minute, and run east and west. I have a piece of slate containing several of these veins, some of which are not larger than the fiftieth part of an inch: and they so thickly intersect the slate, and are so closely connected with it, as to make their origin appear very doubtful.

The apparent veins of magnetic iron pyrites, which are numerous in the Crown rock at Botallack, had they been really veins, would, perhaps, find their place in the doubtful order: they are from one to two inches in width; but as their inclination, which is towards the west, is exactly conformable to the dip of the strata of the rock, they must rather be considered as beds.

THIRD ORDER.—TRUE VEINS.

This order comprises all that are generally acknowledged as true veins, especially all the

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lodes. These may be divided into several classes, the periods of whose formation appear to be different.

Before I attempt to distinguish those classes, it will be necessary to define the terms which are generally applied by the miners to the different kinds of lodes.

By a lode, I mean a metalliferous vein.*

By east and west lodes, metalliferous veins whose direction is not more than 30°. from those points.

By contra lodes, metalliferous veins whose direction is from 30°. to 60°. from east and west.

By cross-courses, veins whose direction is not more than 30°. from north and south.

By flukan veins, veins of whitish or greenish clay, generally argillaceous.

By cross flukans, veins of this clay having the same direction as the cross courses.

By slides, veins of slimy clay, greatly inclined, having generally an east and west, and rarely a north and south direction.

The FIRST CLASS of these veins, in point of age, consists, probably, of the oldest tin lodes. I have divided the tin lodes into two classes, because several instances have been discovered, in which, at the meeting of two tin lodes, one of

* The name lode is given by the miners to every vein which appears likely to produce metallic substances.

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them is traversed and heaved* by the other. It may be stated in general, (although not without exceptions,) that the tin lodes which underlie northwards, are traversed by those which underlie towards the south. I conclude, therefore, that the former, which form a very large majority of the whole, are the oldest. In this class are included most of the lodes in the tin parishes of St. Agnes and Wendron, and a considerable number of the lodes of St. Just; those also in the mines of Huel Vor, Hewas Downs, Huel Unity, Pednandrea, Relistian, Trevaskus, Nangiles, &c.

That these lodes are traversed by other tin lodes which underlie in an opposite direction, may be seen in Huel Trevaunance, (Plate II, fig. 5.) Sealhole, Huel Coates, and Huel Owls.†

* I use the term "heaved" as applicable only to a longitudinal shift of the vein, and "thrown up," or "thrown down" to those shifts which take place on the meeting of two veins, underlying in different directions, in their downward course.
In describing the heave of lodes as to the right, or left, I mean that when lodes are heaved by other veins, they may be found on the other side of the traversing veins, by turning either to the right, or left hand. I use these terms in preference to the points of the compass, because, in whatever direction a miner may pursue a lode, a right, or a left hand heave, is precisely the same on both sides: but a heave to the north, south, east, or west, supposes that on one side of the traversing vein, the lode is in its original direction, whilst on the other side, it is heaved: but although this is probably the true state of the case, it is not easily discoverable, unless the heaves are considerable, on which side a lode has been shifted from its proper course.

† In Sealhole, the great tin lode, which underlies south, traverses three tin lodes which underlie north, and throws all of them up two fathoms. All the reins appear bent, on each side of the traversing vein. (Plate II. fig. 1.)
In Huel Coates the intersection is longitudinal. The great lode underlying south, and running nearly east and west, intersects several small lodes which run south of east, and north of west, all of which are heaved about a foot to the right.
The tin lode of Huel Owls, in St. Just, runs nearly north-west and south-east, and traverses every other tin lode which it meets.

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SECOND CLASS. The more recent tin lodes, in Which are comprised most of those which underlie southwards. To this class probably belong a few of the lodes in St. Agnes, and a considerable number in St. Just.* Those of Poldice, Huel Peever, Treskirby, Gwallan, &c. have a southern underlie; but they have not been seen in connexion with lodes which underlie in an opposite direction.

A particular description of tin lodes will be found equally applicable to both these classes.

Their veinstones are various. In some cases quartz, as in Huel Gorland, the great tin lode in Poldice, the Little Minver lode in Polgooth, &c. In others, chlorite; as in Huel Unity, Relistian, Carleen, &c. Frequently a mixed stone, called by the miners capel, which in

* In the Parish of St. Just, there is a valley called Nancherrow bottom, which divides nearly the whole parish in a direction from E.S.E. to W.N.W. or nearly so on the whole, although its course is serpentine, from its commencement to the sea. South of this valley nearly all the lodes underlie north; as in Huel Bellon, Little Bounds, Huel Dower, Huel Diamond, Balswhidden, &c. North of the valley the lodes generally underlie south; as in Botallack, Huel Cock, Huel Owls, Carnyorth, Parknoweth, Huel Spearn, Boscagel, &c. Some instances to the contrary have been found on both sides of the valley; but they are very rare.

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Rosewall-Hill appears to be quartz and shorl; in Huel Unity, quartz and mica; and in several lodes in St. Agnes, chlorite, shorl, and quartz. Of some lodes in St. Just, decomposed granite forms a considerable part.* Shorl and fluor are rarely veinstones of tin lodes, but tin has been found in the former at Zennor, and in the latter at Huel Malkin.

The length and depth of tin lodes, or indeed of any metalliferous veins, have never been ascertained. Their width varies from that of a barley-corn to 36 feet.† The average width may be stated at from one to four feet: it is, however, not at all regular: the same lode may vary in size from six inches to two feet, in the space of a few fathoms.

Their direction is also various:‡ generally from 5° to 15°. south of east and north of west: in some cases due east and west;§ and less frequently, north of east and south of west.‖ The tin lodes of St. Just vary more from an

* The lodes are not composed of this substance; but bunches of it are frequently found in them, when in a granite country. It is considered favourable to tin.

† Only one lode has been found in Cornwall so large as this, and that only for 20 fathoms in length, in Relistian, In Nangiles, the tin lode is, in some parts, 30 feet wide.

‡ I give the direction as I have received it from the miners, with reference to the magnetic north. If it had reference to the true north, I have no doubt most of the veins, except those of St. Just, would appear to run north of east, and south of west.

§ In Treskerby, Huel Sparnon, Poldice, Polgooth, Huel Coates, &c.

‖ In Huel Vor, Huel Gorland, Nangiles, &c.

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east and west direction, than most others in Cornwall They point nearly south-east, and north-west, and might well be called contra tin lodes. The direction of the lodes of Polgooth is very singular. One of them points nearly north and south, and is therefore a cross course: the only instance, I believe, in Cornwall, of a cross course being rich in tin. Two other lodes point north-west, and south-east; the direction of contra lodes.*

The average underlie of the tin lodes is about two feet per fathom. The greatest underlie I have heard of is ten feet, and occurs in the lodes of Sealhole, and Huel Trevaunance: on approaching the gossan or copper lodes, their underlie increases to 16 feet. (See fig. 1.)

None of the tin lodes have been traced more than two miles in length. Those of Huel Peever and Poldice only, have been traced so far. The Huel Vor lodes have been traced about a mile and half.

Pryce observes† that in his day, tin lodes rarely continued rich, or worth working, beyond

* The contra lodes and cross course at Polgooth, all rich in tin, are traversed and heaved by the great east and west tin lode, as well as by the elvan course, and are therefore probably older than either of the latter. They must be regarded as exceptions to the general rule.

† Min. Cornub. Preface, page 8. The fact was, perhaps, that the expence of draining mines, as compared with the value of their produce, was so much greater fifty years ago than it is at present, that although lodes might have been equally rich in deeper parts, the produce was insufficient to meet the increased expence of draining.

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50 fathoms deep: but of late years the richest mines in Cornwall have been much deeper. Huel Vor, which has lately produced 1500 blocks or 250 tons of tin in three months, is 120 fathoms under the surface. Hewas Downs is 140 fathoms, and is said to be more productive at that depth than in any other part. The lodes of Huel Ann were richest at the depth of 80 fathoms; Trevenen at 150, and Poldice at 120 fathoms.

In order to prove, on the principles already laid down, that the tin lodes are the most ancient of the true veins, it must be shewn that they are traversed by true veins of every other description.

By east and west copper lodes; as at Poldice*, Nangiles, Huel Peever† the Pink and Blue Hills‡, Sealhole§, North

* Here two tin lodes are traversed by one copper lode, and both are heaved about twelve feet. In Nangiles, two copper lodes traverse one tin lode, which is heaved by both of them.

† This mine presents the most extraordinary instances of the intersection of different veins, of any in Cornwall, A description of them by John Williams, Jun, Esq. is inserted in the 4th vol. Geol. Trans. The tin lode, underlying south, is met in its downward course by a copper lode underlying north, and thrown up eight fathoms. It is also traversed by two slides, both underlying north; by one of which it is thrown down 14 fathoms, and by the other thrown up nine feet, (Fig, 2.) In another part of the same mine, it is heaved 70 fathoms to the right, by two cross courses, (Fig. 3.)

‡ The tin lodes of these mines, which underlie north, are traversed by at least eight copper lodes underlying south, and thrown up by each of them.

§ Here the tin lodes are thrown up two fathoms by a copper lode, and two fathoms more by another tin lode, (Fig. 1.) A singular heave of tin lodes by a copper lode was observed in this mine some years ago. A part of a very rich tin lode was heaved so exactly opposite to a part of an unproductive lode, as to occasion a dispute between two sets of workmen. (Fig. 4.)
In an old mine in St. Agnes, called Huel Dreath, the back, or top of the tin lode, appeared three times at the surface, by being thrown up twice on meeting with copper lodes. (Fig. 6.)

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Sealhole*, Huel Trevaunance†, &c.

1. I have met with no instances of tin lodes coming in contact with any other copper lodes, than the oldest east and west lodes.

2. By cross courses‡: as at Huel Vor§, Huel Sparnon, North Sealhole‖, Huel Peever, &c.

* Here the tin lode is thrown up 17 fathoms.

† Here the tin lodes underlie ten feet per fathom north, and the copper lodes three feet in the same direction: on their intersecting the tin lodes, the latter are thrown down nearly five feet. In this mine, there is a junction of tin lodes all underlying north. Trevaunance lode, and Pie lode, underlie 10 feet per fathom: the green lode only six feet. The green lode, on meeting the Trevaunance lode, is carried ten feet in the direction of the latter, and then proceeds in its former course. By the Pie lode it is carried 14 fathoms farther in the direction of that lode, and then again resumes its previous course. The lodes whilst together are easily distinguished. (Fig. 5.)

‡ The shifts of lodes by cross courses and cross flukans, must, of course, be always longitudinal.

§ In this mine there are three cross courses which affect the lode in a different way. For several fathoms on each side of the western cross course, the lode is divided into small, and almost worthless branches. The middle cross course heaves the lode 27 feet to the right. By the eastern cross course, the lode, at the depth of 20 fathoms, is heaved 42 feet to the right; but at the depth of 60 fathoms, only six feet. Some other shifts of this kind will be mentioned hereafter. A small difference in the heave, at different depths, might be owing to a difference in the underlie of the lodes, but when it is so great, can it be accounted for on any other principle than that of a slipping down, or falling off, of the upper part of the country, at a larger angle than the lower part on one side of the cross course?

‖ Here the tin lode is heaved six feet to the right, whilst a neighbouring copper lode is heaved by the same cross course 16 feet, (Fig. 8) The copper lode is intersected at a larger angle than the tin lode.

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3. By cross flukans: as at Huel Vor*, Huel Unity, Huel Gorland, &c.

4. By slides: as at Huel Peever, (fig. 2.) Gwallan, Huel Vor, Polgooth, Blue Hills, Treskirby, (fig. 15.) &c.

A fine view of tin lodes of both classes, and of their intersections, may be obtained at Carclase mine, near St. Austle, which is open from the surface. The country is a decomposed granite, of a greyish white colour: the lodes, which are composed of quartz and shorl, being of a blackish colour, and seldom more than six inches wide, the contrast is very visible. The lodes of the oldest class are nearly perpendicular: some of them have a small inclination towards the south: the more recent lodes underlie rapidly southwards, and traverse the others.

When tin lodes come in contact with the junction of the granite and slate, the apparent effect is very different, in different parts of the mining district of Cornwall. In some of the St. Just mines, viz: Botallack, Little Bounds, &c. when the lodes are between the two rocks, one of the walls being granite, and the other,

* Here there is a cross flukan about 15 feet from the middle cross-course. The lode was much richer between the flukan and the cross-course, than before it came in contact with either.

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slate, they are richer than on either side of the junction. This is also the case in Treskirby, In Huel Unity, and Cook's Kitchen, there is scarcely any perceptible alteration in the lodes, either at the point of junction, or beyond it. But in the parish of Breage, in the neighbourhood of the granite peak called Godolphin Hill, the tin lodes are "wrung up" and almost "cut out " by the slate where it joins the granite, and vice versa. The lodes in the slate may be almost said to terminate with the slate. On the eastern side of the hill, the lode of Carleen, (a compound of quartz, chlorite, and mica,) which is a continuation of one of Huel Vor lodes, was rich in tin nearly to the extent of the slate; but nothing more than "a small string" has been found in the granite. The junction at this point is immediate, and without confusion: the slate overlies the granite at an angle of about 45°. The lodes in the granite present the same appearance on entering the slate: on the northern side of the hill, the lodes of Huel Breage, and the Great Work, (composed of quartz and chlorite,) were rich in the granite, and were wrought to its extreme point, in several levels; but nothing more than a minute branch could ever be found in the slate. The junction on this side is more confused. The granite and slate appear (as the miners term it)

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jumbled together, between the decided slate, and the decided granite.*

Most of the productive tin lodes in Cornwall have been found in a slate country: as Polgooth, Hewas, Huel Peever, Pednandrea, Huel Vor, Relistian, Trevaskus, and all the St. Agnes mines. The lodes of Wendron are generally in granite. Those of St. Just, in both.

Besides tin, the ores of other metals, which are generally supposed to be some of the oldest, have been found in tin lodes, viz. Wolfram, in Poldice and Relistian, and also in a lode at Kit-hill: mispickel in Relistian†; and native bismuth in Botallack. Phosphat of iron, also, has been found in some of the small tin lodes of Huel Kine, in St. Agnes. Chalcedony was found in the tin lodes of Trevaskus and Pednandrea; and jasper in that of Ding Dong.

THIRD CLASS. The oldest east and west Copper lodes. These form the great majority of all the copper lodes of Cornwall.

* In one part of Tregoning Hill the granite appears to be regularly stratified.

† In this mine was discovered, in the tin lode, at the depth of 75 fathoms, a mass of chlorite shist pebbles, cemented by the same substance, with oxide of tin and copper pyrites in the crevices. A few large pebbles were composed of rich tinstone, but in general, the pebbles were wholly destitute of tin. Must we not suppose that these pebbles, however they came there, were formed previously to the tin? So numerous and various were the crystals of tin in this lode, that Mr. Phillips told me that, of those which he has engraved in his paper on the oxide of tin, he had obtained from this mine alone, a greater variety than from all the other mines in Cornwall.

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Their veinstone is generally quartz. In some lodes, as in Huel Gorland, and Huel Unity, it is fluor.* In Dolcoath, Treskirby, and Huel Alfred, quartz and fluor are mixed. In some of the lodes of the United mines, and Huel Virgin, it is capel.† In Huel Squire, and in others of the United mines lodes, it is chlorite. In Chace- water it is hornstone and porphyry. In West Huel Unity, it is, for a short space, chalcedony. Those lodes are considered the most promising, which are composed on the back, or not far below the surface, of a rusty iron ore called gossan, either mixed with the usual veinstone, as in Huel Gorland and Huel Virgin, or being itself the veinstone, as in Cook's Kitchen.‡ Sometimes blackjack, or blende, is closely connected with the copper ore, as in Baldue, Nangiles, Huel Ann, &c: and it is considered a favorable symptom to find, on the back, tin ore, as in Huel Virgin; lead ore, as in Huel Alfred; or pyrites, as in Crenver.

Copper lodes of this class are considered very large, if they are six feet wide. Cook's Kitchen great lode is twelve feet, and West Huel Virgin

* The fluor spar occurs partially when the lode is in the slate; but more generally when it is in the granite.

† See the veinstones of the tin lodes.

‡ Gossan is found at all depths in the lodes, and is generally supposed to indicate a course of ore under it. In St. Agnes, however, there are numerous gossan lodes in which scarcely any copper has yet appeared.

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lode nine feet; but the average width is not more than three feet.

The direction of most of these lodes is south of east, and north of west, perhaps 10°. on an average. In Penberthy Crofts, West Huel Fortune, Huel Alfred, &c., they run nearly east and west. In many other mines, as Poldice, Huel Fanny, Cook's Kitchen, &c., they run from 5°. to 20°. north of east, and south of west.*

The principal east and west copper lodes are, 1. The old lode in the United mines, which has been traced from a part of the parish of Camborne, through Carn-kye, to the mine of Baldue, a distance of seven miles. No other lode has been traced so far.

2. Huel Fortune and Huel Virgin lode, which has been seen for almost three miles in length, from the eastern part of Huel Fortune, to the top of Carn-marth Hill.

3. Huel Damsel and Huel Maid lode; two miles.

4. Huel Gorland, Huel Unity, and Creegbraws lode; two miles.

* Dr. Berger observes that the French used to call veins pointing E. S. E. and W. N. W. "filons du matin." The Cornish miners have carried this idea much farther. They call veins whose direction is due east and west, six o'clock veins; and the north and south veins, twelve o'clock veins: the veins, therefore, which run fifteen degrees N. of E. and S. of W, are five o'clock veins; and those which run fifteen degrees S. of E. and N. of W. seven o'clock veins: those which point N. E. and S. W. are three o'clock veins: and those which point S. E. and N. W. are nine o'clock veins. The same mode of describing the direction of veins appears to obtain at Freyburg.

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5. The lode of Huel Nancy, Camborn-vean, Huel Gons, Straypark, Dolcoath, and Cook's Kitchen; a mile and half.*

6. Huel Towan lode; a mile and half.

7. The lode of Binner Downs, Huel Sarah, Huel Abraham, Oatfield, Crenver, and Trenoweth; two miles.

8. West Huel Fortune, Kestal, and Penberthy Crofts lode; three miles.

9. Huel Alfred lode; one mile.

The underlie of the copper lodes is various. In a line drawn from either Huel Fortune, or the United Mines, to Huel Alfred, they generally underlie northwards;† which, indeed, is the direction of the underlie of a very large majority of all the copper lodes.

The lodes on another line, south of the last, extending from Trenoweth, through Huel Abraham, Godolphin, &c. to West Huel Fortune, generally underlie southwards‡. One of the lodes of Huel Fanny underlies north to the depth of 70 fathoms: below this depth it

* This lode is so disordered by cross courses at Cook's Kitchen, as not to be accurately traced further eastward. Many miners, however, consider it as the same lode that passes through Huel Fanny, Huel Druid, and Huel Sparnon, from whence its course is through Carnmarth Hill to Huel Damsel, Carrarach, and Huel Maid. This would be nearly six miles.

† In this line there are exceptions in Huel Sparnon, Cook's Kitchen, Dolcoath, Herland, Huel Carpenter, &c.

‡ There are a few exceptions on this line, but they are not so numerous as on the other.

N

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underlies south. The lode of Huel Fortune also changes the direction of its underlie, at the depth of about 40 fathoms. The greatest underlie I have heard of is in Huel Squire, where the flat lode underlies eight feet per fathom. The average underlie is about two feet.

In Cook's Kitchen there are two intersections of copper lodes underlying in different directions. Those which have a northern underlie are traversed by those which underlie southwards: (fig. 16:) the latter are therefore, probably, more recent than the former.*

It has been shewn that the east and west copper lodes always traverse tin lodes, from which we may infer that they are the most recent of the both; and as the oldest east and west copper lodes are traversed by contra lodes, cross courses, cross flukans, and slides, they are probably more ancient than any of these.

1. By contra lodes†; as at Huel Alfred‡, (fig. 17,) Mellanoweth, Huel Neptune, Huel Clowance, Godolphin, (fig. 18,) &c.

* It would be going too far to make a new class, with only two instances; especially as all those veins are traversed by cross courses.

† I do not mention the particulars of any of these intersections, unless they are worthy of notice on their own account. Crenver seems to present an exception to the general rule, as the contra lode in that mine, on meeting the great lode, is carried 70 fathoms in the direction of the latter: it then resumes its old direction.

‡ Here the contra lode intersects the great lode, and carries it in its own direction for 80 fathoms: the great lode then separates and resumes its former direction. The lodes may be easily distinguished when together.

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2. By cross courses; as at the United Mines, Huel Jewel*, Cook's Kitchen†, Gunnis Lake‡, North Downs, &c. Intersections of this kind are so numerous that it is almost unnecessary to select particular instances.

3. By cross flukans; as at HuelSquire§ (fig. 7), Tingtang (fig. 11), Huel Unity, Huel Damsel, Huel Friendship, &c.

4. By slides; as at Treskirby (fig. 15), Huel Squire‖, Herland, Huel Friendship, &c.

In many copper mines, particularly the United Mines, the lodes have been found to be richest on approaching the cross courses, on both sides: but in some other mines, the lodes have been rich on one side of the cross courses; but barren on the other. The lodes of Huel

* The lodes of Huel Jewel are traversed by the great cross course, which is supposed to extend from the Bristol to the St. George's Channel, and heaved to the right, about 70 fathoms.

† The mines of Dolcoath and Cook's Kitchen are divided by a cross course, and the lodes are heaved to the right 50 fathoms.
The intersection of Dunkin's lode in Cook's Kitchen, by the little cross course, is singular. At the depth of 25 fathoms, the lode is not heaved at all: at 54 fathoms deep, it is heaved five fathoms; at 72 fathoms deep, six fathoms; and at 105 fathoms deep, 12 fathoms: all to the right.

‡ In this mine another curious shift occurs. At the depth of 70 fathoms, the lode is heaved 15 feet to the left; and at ten fathoms deeper, it is heaved 15 feet to the right.

§ Pearce's lode in Huel Squire, on meeting with a small cross flukan, is, at the depth of 26 fathoms, heaved eight fathoms to the right: but at 20 fathoms deeper, the heave is only three feet.

‖ Here the slides underlie N. E. very rapidly, and throw down the lodes; but at the same time, they enrich or feed them, as the miners express it; the lodes being richest when near to the slides.

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Jewel and Relistian were rich on the eastern side of the cross courses; but on the western side they were entirely unproductive. Is it not probable from these facts, that, in some cases, although the east and west veins were formed previous to the cross courses, the metallic ores in those veins were formed afterwards?

The junction of two copper lodes longitudinally where there is no apparent intersection, is very common, particularly in some of the Gwenap mines. When the lodes are nearly of the same kind, in point of composition, and underlie towards the same point, the result is generally a great enlargement of the lodes, and a rich course of ore, even when both the lodes were previously barren:* but if the lodes are of different kinds, or underlie in an opposite direction, the result is quite opposite. Lodes meeting in this way, and shewing no kind of intersection, may be supposed to be of the same age: (fig. 19).

In several of the copper mines, there are some lodes of which no trace is to be found at, or near, the surface; but they are discovered either in the adit, or in some deeper level, and on being traced, are found to proceed downwards from some other lode, In Treskirby two of

* Huel Unity and Nangiles are exceptions to this remark. In these mines a junction of lodes longitudinally is rarely productive of riches; but generally the contrary

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these lodes fall off from the old south lode, and in their downward course they unite: (fig. 15). In the United Mines several lodes fall off from Cupboard lode. In Tincroft and Cook's Kitchen also, lodes have been found under similar circumstances*: (fig. 16).

When copper lodes, from a state of poverty, become either gradually or suddenly rich, the change is generally rather in the qualities, than in the constituent parts, of their veinstones: as, from hard quartz or capel, to quartz in a state of decomposition, called by the miners sugary spar; or to soft chlorite, which they call peach. Another frequent change is from a very solid compact lode, to what the miners call a hollow lode, abounding in cavities. Sometimes the lode becomes greatly enlarged.

Most copper lodes are accompanied by small flukan veins; (termed by the miners, the flukan of the lodes). These are probably more recent than any other parts of those lodes, and almost deserve a separate place as veins within veins. They appear sometimes on one, and at others, on both sides of the lodes, and in some cases in the middle. They frequently cross from one

* Mr. Phillips (Geol. Trans. Vol. 2.) appropriately calls these "offsets." I have endeavoured to keep as clear as possible of his paper; but for the sake of connexion I have been obliged to make a few remarks similar to his. I have, however, omitted many circumstances relative to veins, which are not immediately connected with their age, because they have been mentioned in previous publications.

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side to the other. In some instances they have separated from the lode, and, in a few fathoms, have joined it again.*

The veins which have produced tin in the upper part, and copper below, probably belong, some to the class of tin lodes, and others to that of copper lodes†. Only one instance has been known in Cornwall of a lode producing copper above, and tin below, exclusively, viz. the great lode in Cook's Kitchen‡. In Tincroft and Dolcoath, tin is found connected with copper in the lodes, in the deepest parts of those mines. In some copper lodes, tin is so plentiful in some parts, as to give them, for a short space, the appearance of tin lodes.

* I apprehend these are what Werner calls the saalbande. They are, perhaps, the result of fissures in the lodes, occasioned by the consolidation, and consequent contraction, of their parts. In most of the mines of Gwenap, and in many others, they are considered favourable to copper. They are sometimes attendant on tin lodes, but not so generally.

† The great capel lode in West Huel Virgin is called a tin lode, and is traversed by Tregoning's copper lode; but in its downward course the tin declined, and it became rich in copper. On the other hand, Cargruel lode, in the United Mines, which produced tin in the upper part, and copper below, traverses Rapscy copper lode.

‡ This lode is 12 feet wide, runs east and west, and underlies south. Toy's lode, two feet wide, has the same direction, but underlies north. At the depth of 105 fathoms, the great lode was very rich in copper: here Toy's lode fell in with it, and cut out nearly all the copper. Toy's lode is traversed by the great lode, and thrown down 18 fathoms, (Fig. 16.): in this space, the latter contained both tin and copper. After Toy's lode separated from it, the great lode continued its course to the depth of nearly 190 fathoms, as a tin lode. It produced no tin worthy of notice before the intersection, and scarcely any copper afterwards.

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It appears, from the result of long experience, that little is to be expected from copper lodes which may be discovered in what may be strictly called a tin country: the copper-ore is, in such cases, generally found in short bunches, which do not pay the expence of searching for them. This may be proved by a reference to the parishes of Wendron, St. Agnes, St. Just, the southern part of Breage, and the neighbourhood of Polgooth, and Great Hewas mines.*

From the frequent junctions of the granite and slate in the mining districts of Cornwall, many of the copper mines are situated on, or near, the lines of junction. Some of the most productive mines are directly on the lines, viz. Huel Unity, Treskirby, Dolcoath, Cook's Kitchen, &c. In Treskirby, Huel Gorland, Tresavean, and Nangiles†, the lodes improved on entering the granite from the slate. In Huel Unity, Cook's Kitchen, and Dolcoath, scarcely any alteration was perceptible.‡ In Botallack, Huel Cock, and other mines in St. Just, the copper lodes are more productive in the slate than in the granite, but they are richest on the

* Huel Towan, which may be cited as an exception to this rule, is not in the tin district of St. Agnes. In Huel Unity and Poldice, there are very productive tin lodes; but they are in a copper country.

† Here the lode, which, in the slate, was principally quartz, became, in the granite, a flukan lode.

‡ In all these mines, a much larger quantity of ore has been raised in the slate than in the granite country, because the ore has extended much further in the lodes when in the slate.

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line of junction, especially when one wall is granite, and the other, slate. This is also the case in Treskirby, and was formerly so in Carrarach. On the whole, however, the slate country may be considered more favorable to copper, than the granite. Several rich and extensive copper mines have been wholly in slate; as Huel Towan, Huel Alfred, Herland, United Mines, Huel Virgin, Crennis, &c.; but I apprehend there is not one which is wholly confined to granite.*

The following minerals have been found in east and west copper lodes. Stalactitic, botryoidal, and investing chalcedony: stalactitic, swimming, and cubic quartz; and rounded shist pebbles; all in Huel Alfred: red jasper, in West Huel Unity: sulphat of barytes in the United Mines†: wolfram and oxide of uranium, in Tincroft, Tolcarne, and Gunnis Lake‡: sulphate of lead in Mellenoweth§: petroleum in

* Huel Damsel, Huel Jewel, Tresavean, and Huel Gorland, are not wholly in the granite. The slate appears in the eastern part of all those mines.

† It was found in the great south lode, from the depth' of 100 to 160 fathoms, and generally preceded a rich course of ore.

‡ The uranite is in four-sided laminæ. It has been found from 23 to 60 fathoms deep, at the point where an east and west copper lode is intersected by a contra lode. The finest specimens were found in the deepest part.

§ The gossan, or top of the copper lode, was full of crystals of this substance, of which I have seen the quadrangular prism, with its pyramid; the rhomboidal prism, and the octahedron, with several modifications.

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Treskirby, Huel Unity, and Carrarach: arseniate of cobalt, in Dolcoath: grey silver ore and native silver, in Huel Ann*: kupfer nickel, in Pengilly, in the parish of St. Ewe. The arseniate of copper was found in Huel Unity, where the lode was between the granite and the slate. The arseniate of lead occurred just at the junction of a contra lode, with an east and west lode.

FOURTH CLASS. The Contra Copper Lodes. The contents of these lodes are nearly the same as those of the east and west copper lodes, the only difference lies in their having more flukan in their composition.

They are in general wider than the east and west lodes. Huel Neptune lode is twelve feet wide. Huel Alfred, nine feet; Crennis, ten to fifteen feet. The average width may be stated at four feet.

Their direction is in general from 30°. to 45°. south of east, and north of west: some however run in a directly opposite direction, viz. north-east, and south-west; as in Huel Gorland, United mines, Huel Friendship, Penberthy Crofts, &c.†

* These were found in a small vein, having distinct quartz walls, in the middle of the copper lode.

† The miners give the name of contra to every lode which is much out of an east and west direction, and crosses the lodes which run east and west: but I am not aware that east and west lodes are traversed by any contra lodes which are not at least 30 degrees from those points.

O

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Their underlie is much the same as that of the other copper lodes: about two feet per fathom on an average.

They are very few in number, compared with the east and west lodes; and none of them have been traced so far. The Herland contra has been traced three miles, and the Huel Gorland great gossan, about a mile. I believe no others have been traced farther.

They are as productive of copper as any other lodes: of this the contra lodes of Huel Alfred, Crennis, and Huel Neptune, furnish sufficient proof.

They (as well as the east and west lodes) are usually accompanied by small flukan veins, which are probably more recent than the other parts of the lodes.*

No instance has occurred in which contra copper lodes are traversed by any of the veins which have been already described: they are traversed however by veins of other descriptions, viz.

1. By cross courses: as in the United Mines †, Herland ‡, amp;c.

* In Huel Alfred a flukan always accompanied the contra lode, in some parts on one side; and in others, on the other. When it was on the south west, or lower side, the lode was much richer than when it was on the opposite side: it at length separated from the lode, whose riches immediately began to decline: in the deepest level, it was 15 feet from the lode, and here the barrenness of the lode obliged the adventurers to abandon the concern.

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2. By cross flukans: as in Huel Gorland, Huel Fanny §, Godolphin, Huel Alfred (fig. 17), Crennis, Huel Treasure, &c.

3. By slides, as in Huel Neptune, Huel Friendship, &c.

The beautiful specimens of arseniate of iron which were so plentiful some years ago, were found in a contra lode, viz. Huel Gorland great gossan: and in Crennis lode have been found some specimens of fahlerz.

FIFTH CLASS. Cross Courses. These veins are sometimes composed wholly of quartz, but they usually contain, besides quartz, a large portion of flukan, and in some cases the quartz appears on one side of the vein, and the flukan on the other: when this is the case, the flukan is probably the most recent part of the vein. Many cross courses have a portion of gossan in their composition: these are called cross gossans.

The width of these veins is greater, and more variable, than that of the tin and copper lodes. One of the cross courses in Huel Vor is 36, and

† Here there are two contra lodes, called Cargruel lode, and Trelease's contra, both of which are traversed by a cross course in one part of the mine, and in another part by a cross flukan: by the former they are heaved 12 feet; by the latter 16 fathoms.

‡ Here the cross course carried the contra lode with it for about eight fathoms. In this space the two veins appeared as one, and the whole was rich in copper ore.

§ Here the lode is not heaved, but appears bent on each side of the flukan.

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another, 20 feet: the Huel Peever cross course is 20, and that of Carrarach, 12 feet. Their average width is at least 6 feet.

Their direction is sometimes north and south: sometimes west of south, and east of north, but most frequently west of north, and east of south; seldom exceeding 20°. on either side.

Their underlie is as various as their direction; but it appears that most of those which point east of north, underlie towards the west; as at Penberthy Crofts, Huel Alfred, Weeth, and Huel Carpenter; and the greatest part of those which point west of north, underlie towards the east: as at Huel Vor, Huel Squire, North Sealhole, United Mines, &c.

These veins are sometimes the cause of incalculable trouble and expence to the miner, by shifting the lodes from their usual course, by deranging their contents, and oftentimes by cutting out all their riches. On the other hand they are sometimes advantageous, as that part of them which consists of flukan is quite impervious to water.

The principal cross courses in Cornwall have been traced from the shore of the Bristol Channel, near Porth Towan, through St. Agnes and Illogan Parishes to Huel Peever. In the cliff they are at some distance from each other, and between Porth Towan and Huel Peever, they traverse all the veins in their way, and heave

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them, the eastern cross course 54, and the western, 18 fathoms. In the southern part of Huel Peever they unite, and form one course of four fathoms wide, which, after heaving the lodes of Huel Jewel about 70 fathoms, continues its way to some confused ground near Huel Damsel, south of which it heaves the lodes only 16 fathoms. It has been traced nearly eight miles.*

The other cross courses most worthy of notice are Tiddy's great cross course in the United Mines, Paul's cross course in Huel Virgin, the cross courses in Mellanear, Huel Alfred, Weeth, Relistian, Huel Sarah, Huel Vor, Cook's Kitchen, &c. of these the Huel Vor cross courses have been traced two, and that of Relistian, three miles.

To the class of cross courses probably belong the large north and south veins which traverse the whole of the extensive parish of St. Just. They are called by the miners " guides," because they suppose that by following those veins, they will be conducted to the tin lodes; but they may with more propriety be termed iron lodes, as they contain, besides quartz and clay, brown

* Dr. Berger says it terminates at Pedn Boar point: (Geol. Trans. vol. i. page 165.) but its termination has never been discovered, and for the space of five miles before it reaches the southern coast, it has not been traced at all, as, at a short distance from Huel Squire, it leaves the mining district: but a line drawn from Huel Peever, through its last visible point, would find its termination at, or near, Swan pool, a mile west of Falmouth.

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iron-stone, specular iron ore, brown haematite, &c. Two of them have been traced three, and another, five miles. When they intersect the lodes, they generally carry them several fathoms in their own direction, before a separation takes place. In such cases the lodes are frequently much improved. In two instances which occurred in Botallack and Parknoweth, very rich courses of tin have been the result of such intersections.*

It has been shewn that cross courses traverse all the true veins which have been already described: it remains to be shewn that they are traversed by other veins.

1. By the more recent copper lodes: as at Penberthy Crofts, Huel Alfred, (fig. 17,) Huel Smart, and the Weeth.†

2. By cross flukans: as in the valley north of Huel Damsel‡, and at Huel Alfred.

* I have been told that one of those veins is twice shifted from its usual course by tin lodes; but as the mines in which those shifts are said to have occurred are not now at work, it cannot be ascertained whether the statement is correct; and as the accounts which I have obtained are various and contradictory, I am not at all satisfied of their occurrence, especially as in every other instance where those veins and the tin lodes meet, the latter are traversed by the iron lodes. The mode of working the St. Just mines renders it, in most cases, difficult to ascertain satisfactorily the result of the intersection of different veins.

† This is a singular intersection. Two cross courses are traversed by the same east and west lode. One, whose direction is ten degrees west of north, and east of south, is heaved three fathoms to the left: the other, which points about ten degrees east of north, is heaved three fathoms to the right, (Fig. 12.)

‡ This valley is intersected by the large cross course which is supposed to run from sea to sea, and this cross course is traversed completely, by a cross flukan. The country in a part of this valley bears the marks of convulsion, being in great disorder and confusion. The cross course evidently partakes of this disorder, but the flukan appears to bear no marks of it. If therefore there had been no intersection, there would be no difficulty in ascertaining the comparative age of those two veins. The Weeth also furnishes an instance in proof of the more recent formation of cross flukans: the north copper lode traverses two cross courses, and is itself traversed by a cross flukan.

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3. By slides: as at the Garres*, Polgooth†, and Herland.

It is not at all strange that so few instances have been met with of the intersection of cross courses, by cross flukans, and slides; for however frequently these may occur, they are not likely to be discovered, except in adits which may be driven in the same direction; or unless they happen just at their intersection of metalliferous veins; for, in general, those cross veins have nothing valuable in themselves, to make them worthy of pursuit.‡

* This is a lead mine near Truro, the lead being found in a cross course, which is intersected by two slides, by each of which the lead vein is thrown up six fathoms.

† Here Screed's tin lode, which is a cross course, is heaved by a slide. — I am aware that there are two instances in Huel Peever, in which the slides are traversed by the cross courses. In these cases, it is probable that the slides are the oldest: but I believe the slides are in general the most recent; 1, because of their composition, which is wholly clay: 2, because some of the east and west lodes which traverse cross courses, are found to be traversed by slides.

‡ It is much to be desired that a plan and a section of every mine should be made, and exposed to view in the account house. The utility of this is strikingly proved by the circumstances which occurred in Dolcoath. After cutting through the cross course by which the great lode was traversed, a lode was discovered on the opposite side, about three fathoms to the right, which was supposed to be the great lode, and was pursued as snch, until a correct plan of the mine was made: it then appeared probable, from the direction of the lodes, and other circumstances, that the newly discovered lode was not the great lode. The latter was afterwards discovered at the distance ef 50 fathoms. (Fig. 9.)

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Cross courses are in general unproductive either of tin or copper; but some rare instances have occurred in which both these metals have been found in them. In Polgooth, Screed's lode, which is a cross course, was rich in tin. In Huel Music, two small gossan cross courses have produced some of the richest copper ore in Cornwall. In Huel Jubilee also the copper lode is a cross course. It, however, frequently happens that cross courses, on intersecting rich copper or tin lodes, partake of their riches for a short space. In Huel Peever, the cross course was rich in tin several feet north of the point at which it intersected the tin lode; and in Treskirby, Kinsman's cross course was rich in copper for about ten feet north of its intersection of a copper lode; but on the southern part they were quite barren.

Lead is the principal metal found in cross courses, in Cornwall: but at present there are very few lead mines wrought. Pentire glaze* near Padstow, and Huel Golding in Perranzabuloe, are the principal mines in which the lead occurs in cross courses.†

* This mine has lately produced the finest cabinet specimens of carbonate of lead ever known in Cornwall, or perhaps in Great Britain.

† Dr. Borlase in his Nat. Hist. of Cornwall, observes that the lead veins of Cornwall generally run east and west. This is not correct, for, except in one instance, the lead veins are cross courses.

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The following substances also, have been found in cross courses, viz. Arseniate of cobalt, at Huel Trugo and Huel Sparnon.* Sulphuret of antimony, and the triple sulphuret of antimony, lead, and copper; at Huel Boys†. Native silver, and several ores of that metal, at Huel Mexico, Herland, and Huel Basset. Petroleum, at Huel Jewel.

SIXTH CLASS. The more recent Copper Lodes. This class will comprize the east and west, and also the contra lodes, which have been found to traverse not only other copper lodes, but cross courses also. They are not numerous, but they may be seen at Penberthy Crofts, Huel Alfred (fig. 17), Huel Smart, and the Weeth (fig. 12).

There is nothing in their size, direction, or underlie, which distinguishes them from the copper lodes which have been already described; but with respect to their composition, they must be styled flukan lodes, having more clay in them, than is usually seen in the cross courses.

In this class must probably be placed the lead veins which have been lately discovered

* In both these mines the cobalt was found in some parts of the cross courses in regular veins; and in others, in small bunches. In Huel Sparnon, one solid mass was brought to the surface, which weighed 1333 pounds.

† The vein is about one foot wide, and has been wrought to the depth of 36 fathoms. It has yielded as much as 100 tons in a year of regulus of antimony, containing eight parts in twenty of pure antimony; but it does not now produce half that quantity.

P

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in the parish of Newlyn, by Sir Christopher Hawkins, in draining a marsh. They are about two feet wide, and run nearly east and west: a direction contrary to that of almost all the other lead veins which have been hitherto discovered in Cornwall. Besides the lead, and a little quartz, they consist entirely of clay. Neither copper nor tin has been seen in them. Those veins are far richer than any north and south veins in which lead has yet been found. The lead yields about sixty ounces of silver per ton.*

The veins of this class are traversed

1. By cross flukans: as at Penberthy Crofts, Huel Alfred (fig. 17), and the Weeth (fig. 12).

2. By slides: as at Penberthy Crofts.

SEVENTH CLASS. The Cross Flukans: or cross courses which are composed wholly of clay†. They vary in width, from the smallest imaginable size to nine feet, but their average width is not so great as that of the cross courses, as most of them are less than one foot wide. However small they may be, no water can percolate through them.

Their general direction is nearly north and south: their underlie is much the same as that

* This paragraph has been added since the reading of the paper, as those veins were then scarcely known.

† The miners give to cross flukans in general, the common name of cross courses, unless they are very small: they are, then termed simply " flukans."

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of the cross courses: generally towards the east.

The results of the intersection of tin and copper lodes by cross flukans, are nearly the same as those which attend cross courses. Most of the heaves by these veins are to the right.

The arseniate of lead was found at Huel Unity, just at the point where a cross flukan insersected a copper lode.

The cross flukans traverse every kind of vein but the slide; and Herland presents the only instance which I have been able to find, of the intersection of those two veins. In that mine a slide, of the width of three inches, traverses several cross flukans.

When a miner, working on a lode, meets with a cross course or cross flukan, he generally cuts through it*. If the lode is heaved, he endeavours to ascertain where he will probably find it on the other side; 1, from its having been discovered in other levels in the same mine; 2, from the manner in which other lodes near it, having the same direction, are shifted by the same cross vein; 3, by searching for some of the component parts of the lode on one side of

* Unless he wishes to let it remain for the purpose of preventing an influx of water from the other side. In some cases, where a lode has been poor, the adventurers, on meeting with a cross course, have, in despair, abandoned the concern; but the previous poverty of a lode ought, in all cases, to be a strong reason for cutting through the cross course.

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the cross vein; 4, by observing the direction in which other lodes in the neighbourhood are heaved by other cross veins. If his judgment can derive no assistance from either of those circumstances, he will naturally drive at first on the right hand, because in most cases, lodes are heaved to the right: if, after driving a few feet, the lode is not discovered, he will turn to the left, and drive the same distance: if this is unsuccessful, he will return to the right, and again to the left; and thus he will continue until he has discovered the lode.

It has been laid down as a rule,* that when a lode is heaved, the part broken off is to be found on the side where its junction with the cross vein makes the smallest angle (fig. 13); but nothing is more uncertain than this. In Huel Vor, all the lodes are found on the side of the largest angle (as in fig. 14). In the United Mines, all the lodes are heaved to the right; and as their direction is different, some are found on the side of the smaller, and others on that of the larger angle of intersection. This is also the case in Huel Unity, and Huel Gorland, where all the lodes are heaved to the left. In Huel Squire there are some heaves to the right hand, and others to the left; but most on the side of the larger angle (fig. 7).†

* Pryce, page 99.

† Tingtang furnishes an instance of four heaves, by three cross flukans, and a cross course, within a very short space; all to the right; but as the direction of the flukans is different, the angles of the heaves are also different, (fig. 11.)

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Neither does the direction of the heave appear to depend on the underlie of the lodes, or the cross courses. In Huel Squire, Andrew's flukan underlies towards the east, and all the lodes towards the north, yet they are all heaved to the left: the same circumstance occurs in Huel Unity. Odgers's and Morcom's flukans in Huel Squire, underlie towards the east, and the lodes towards the north; but the lodes are heaved to the right. In Cook's Kitchen, three lodes underlie northward, and two towards the south: the great cross course underlies to the east, and the little cross course to the west: yet all the lodes are heaved to the right by both the cross courses.

The distance to which one part of a lode is shifted from the other, by a cross course, or cross flukan, does not at all depend on the size of the cross vein.* In Huel Virgin, a cross course, two feet wide, heaves the lodes nearly six fathoms; and in Huel Peever, another of the same width heaves the lode 18 fathoms: whilst in Huel Sparnon, a cross course of the width of eight feet, heaves the lodes only two fathoms. In like manner, a cross flukan in Huel Unity, 18 inches wide, heaves the lodes five fathoms:

* Pryce has asserted The contrary, with respect to slides and copper lodes, or gossans, as he calls them; (page 106, 107,) but I am persuaded, incorrectly.

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another in Huel Squire, of the width of two feet, heaves the lodes 19 fathoms: and a very small one in Huel Daniel heaves the lodes 14 fathoms: Whilst in the United Mines, a flukan above two feet wide, heaves the lodes only one fathom.*

It will doubtless have been observed, in the description of the copper and tin lodes, that most of those lodes, on meeting with cross courses, or cross flukans, are shifted in such a manner as to be found by turning to the right hand. Left handed shifts are comparatively few. From the appearance of many of the lodes, and the alteration in their general direction, on the western side of the cross courses; and from some of the cross courses being rich in copper and tin for several feet north of their intersection of copper and tin lodes; I conclude that, of the lodes which appear to be heaved to the right hand, the western branches have been shifted towards the north. Whether the eastern branches of the lodes which are heaved to the left, have been also shifted towards the north, there are not the same grounds of deciding. The probable cause of these shifts, and the mode in which they have been effected,

* The lode of Crennis is stated to be heaved 200 fathoms, by a flukan of eighteen inches wide; but this immense distance makes it probable that what are supposed to be two branches of the same lode, are really two distinct lodes; especially as there are no corroborative circumstances to make such a fact probable.

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cannot be discussed without involving theories which have little immediate connexion with the relative age of veins.

EIGHTH CLASS. The Slides: probably the last class of true veins; being found to traverse veins of every other kind.* They are composed wholly of clay, which is generally of a more slimy nature than is often found in other veins.

They run in all directions; but their general direction is nearly parallel with that of the tin and copper lodes. Instead therefore, of heaving them longitudinally, as the cross veins do, they either throw them down, or throw them up: the former when they underlie in the same direction as the lodes: the latter, when in an opposite direction.†

These veins are generally very small: seldom more than one foot wide; and they usually underlie very fast, which indeed is probably the reason of their being called slides: or perhaps because, when they underlie in the same direction as the lodes, the latter, on meeting them, appear to slide downwards.

There are slides in Treskirby, Huel Squire, Huel Vor, Huel Friendship, Huel Neptune, Gwallan, &c.

* With the exceptions in Huel Peever.

† This is stated in general; but there are some exceptions. In the Garres, where two slides underlie in nearly the same direction as the lead lode, the latter is thrown up by both of them.

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The result of the meeting of other veins with slides has been already shewn in describing those veins, and need not be repeated.

I believe I have now described all the true veins which are found in Cornwall; but in order to exhibit, at one view, the intersections of the different veins, a few instances may be separately repeated.

In Huel Trevaunance, a tin lode is traversed by two other tin lodes: all these are traversed by several east and west copper lodes; and a slide traverses the whole.

In Huel Alfred, the east and west copper lode is traversed by a cross course: both are traversed by a recent copper lode; and a cross flukan traverses them all (fig. 17).

In Herland, the east and west copper lodes are traversed by a contra lode: these are traversed by several cross courses and cross flukans; and all of them are traversed by a slide.

In the Weeth, the south copper lode is traversed by two cross courses, which are in turn traversed by the north copper lode; and both the lodes are traversed by a cross flukan (fig. 12).

In describing the contemporaneous veins, some were mentioned as occurring in the vein-stones of other veins. There are also metallic veins which may be denominated veins within veins.

1. SILVER. In the copper lode of Huel Ann, there occurred a distinct vein of black and grey

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silver ore, with native silver, from two to five inches wide, with a wall of quartz on each side: It was however very short both in length and depth.

2. TIN. The wood-like oxide of tin is frequently found in veins, both in quartz and in tinstone, with which they have the strongest appearance of being contemporaneous. The common tinstone also often occurs in veins, crossing the veinstones of the lodes. The cabinet of the Society contains a fine specimen of this kind, as well as of the silver vein.

3. COPPER. The green carbonate of copper is found in veins, in quartz, which is the veinstone of the lodes, in Huel Carpenter, Huel Neptune, &c. The blue carbonate occurs in the same way in Tingtang; and the arseniate, particularly that variety of it which is called wood-copper, in Huel Unity. Native copper was found in veins, in the quartz of the lode, at Godolphin, and sulphuret of copper, in the same manner, at Huel Jubilee. I have also seen veins of brick-coloured oxide of copper in the lode of Huel Damsel. Those veins have, in most cases, the appearance of a formation posterior to that of the containing veinstones.

4. Iron. Veins of the woodlike oxide of iron are occasionally found in brown iron-stone, and appear to be contemporaneous with it. At Botallack and Boscagel-downs, veins of fibrous

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oxide of iron are very common in the quartz of the lodes, and veins of carbonate of iron at Huel Jubilee.

5. BISMUTH. The native bismuth which was, some years ago, found in one of the lodes of Botallack, occurred in minute veins, in coarse red jasper.

With respect to the relative ages of the several substances contained in the true veins of Cornwall, it is not often that we have many circumstances to guide ns, on which we can safely depend. In general, an ochreous oxide of iron (gossan) is found in the upper part of the copper lodes, to which sulphuret of iron (mundic) frequently succeeds: below this, the miners confidently expect to find copper ore. If, however, the lode becomes barren in its downward course, the gossan sometimes appears again, under the barren part, and is introductory to another bunch of copper ore below it.

In the lodes of Herland and Huel Carpenter, carbonate of copper, and in that of Huel Unity, arseniate of copper, has been found on quartz, of whose crystals they have received the impression. The latter mine has also produced arseniate of lead, of which a mass of minute crystals appears to invest crystals of quartz. From Botallack lodes I have seen brown hæmatite and iron pyrites investing crystals of quartz, and also quartz which has received the impres-

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sion of the hæmatite. In all such cases, where one substance has the form in which it is generally found, and the other a form in which it rarely, if ever, occurs separately, it may be concluded that the latter is the most recent.

The principle on which I have hitherto proceeded in order to ascertain the relative ages of the several classes of true veins, has been entirely that of intersection; and I have mentioned few, if any instances, in which it may not be satisfactorily proved, both from a similarity of size, appearance, and contents, in the broken parts of the lodes; and from the shifting of other lodes in the same way, by the same intersecting veins; that the veins which are described as being shifted, and which are found on the opposite sides of an intersecting vein, are really broken parts of the same vein, and not different veins which terminate where they appear to be broken off. But I think another principle may be deduced from the whole of the preceding remarks: viz. that veins which contain the greatest quantity of flukan or clay, are generally found to traverse those which contain a less quantity, or none at all of that substance. On this principle, the east and west veins, whose veinstone? are quartz, shorl, chlorite, or a mixture of those minerals, with scarcely any clay in their composition, will be found the most ancient. These are the tin lodes. The east and

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west veins, having veinstones of different kinds and containing a small mixture of clay in them, come next. These are the oldest copper lodes. Then come the contra lodes, which contain more clay. Next, the cross courses, in which the quantity of clay is still larger. Then follow the more recent copper lodes, which have a still greater proportion of clay. After these, the flukan veins, and the slides, which are nearly all clay.

I have purposely abstained from speculating on the manner in which the contents of the veins were originally placed in the fissures which contain them. There is one point, however, to which I cannot help alluding, as it has been made to bear on different theories. It has been stated by some, that veins become smaller as they get deeper: others have asserted the contrary: but as far as the earth has been penetrated in this county, it appears evident that neither of these statements can be maintained as a general position. The lode of Huel Abraham, the deepest mine in Cornwall, is larger at the depth of 240 fathoms, than it was nearer the surface. In Dolcoath, the deepest mine next to Huel Abraham, the principal lode was largest at the depth of about 80 fathoms. The lode of Huel Alfred was much larger at the depth of 110 fathoms than at any less depth; but at 150 fathoms deep, it had considerably decreased in

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size. The Huel Neptune lode, which was nine feet wide near the surface, is about the same width at the depth of 130 fathoms.

That part of Cornwall in which most of the veins which have been described are found, has generally been regarded as a primitive country, consisting for the most part of the oldest granite, and of primitive slate, or argillaceous schistus, now generally called clay-slate.

The claim of the granite which forms the chain extending from the Land's end to Brown willy, to the name of primitive granite, has rarely, if ever, been seriously disputed. The supposition that Saint Michael's Mount is transition granite, rests entirely on the occurrence of granite veins which appear to be connected with the granitic mass, intersecting the slate. Perhaps, however, it will appear from the facts which have been mentioned respecting those veins, that, whatever may be their relative age, the mass of granite may still be of primary formation.

The claims of the clay-slate, however, have of late been disputed, and it has been called transition slate, and greywacke slate, by geologists whose authority certainly carries considerable weight: but by what rules are we to distinguish primitive, from transition slate? In its structure, the clay-slate of Cornwall appears, in general, perfectly homogeneous. It contains no im-

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pressions of any kind. Some of the oldest metals have been found in it: viz. oxide of tin, wolfram, and mispickel: these have been discovered in the slate: and they have also been found, together with sulphuret of tin, native bismuth, and oxide of uranium, in the veins which intersect it. Some of the oldest minerals have also been found in it; viz. axinite, garnet, topaz, &c. Are not these some of the strongest marks of a primitive rock? Some specimens of it were sent by a member of our society to Werner, who recognised in them the clay slate of Saxony.

That greywacke exists, and abounds in some parts of Cornwall, will not be denied; but I apprehend it is not to be found, except in small and scattered portions, in that part in which nearly all the tin and copper mines are wrought, It appears to commence near Grampound, and to extend westward about three miles from Truro: how far southward, I have not been able to ascertain. Its extent northward, in mass, is probably not from Truro, but it is found in bunches as far as Padstow, and Tintagel Castle, Near the former place it is highly characterized; and at Tintagel, impressions have been found in it. The lead veins of the Garres, and those of Pentire glaze, and the vein of antimony at Huel Boys, are probably in greywacke; but I have never seen either copper or tin in greywacke, nor am I aware of any tin veins which intersect it.

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It is worthy of observation, that the riches of the east and west lodes which are comprised in the great mass of tin and copper mines, appear to terminate with the clay slate formation eastward. If a line be drawn from, the eastern parts of the mines of Nangiles or Baldue, to the eastern part of the parishes of St. Agnes or Perran, it will form the eastern boundary of the mines. If the lodes of those mines continue in the greywacke, they are generally divided into small branches; but this has not been ascertained, as its junction with the clay slate is so gradual, that the line of division can scarcely be discovered: it however gradually recedes from the clay-slate in character, as in distance; and between Truro and Grampound, its characters are very distinct The clay-slate appears again near Grampound, and there also the lodes and the mines recur. One would therefore almost suppose that a sinking of the clay-slate had taken place in the intermediate space, forming a kind of basin, in which the greywacke had been subsequently deposited; and that the lodes of Great Hewas and Polgooth tin mines, and of Crennis, Huel Regent, and Huel Treasure copper mines, were a continuation of the lodes of the principal mines in the parishes of Redruth and Gwennap.

It will no doubt be observed that the remarks which I have made respecting rock-veins are applicable, for the most part, only to those of

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the western parts of Cornwall. There is a large extent of coast (principally clay-slate) open both to the Bristol and the British Channels, of which little notice is taken. In truth I have not been able to examine any part of the south coast, east of Falmouth Harbour; and very little of the north coast, east of Cligga point. Many veins therefore, different from those which are here noticed, may possibly remain for future description. But when it is considered that, with few exceptions, all the veins which have been described, occur in a tract not more than thirty miles long, and ten miles broad, on an average; I may safely repeat that, in all probability, no other district of equal size can compare with Cornwall in the number and variety of its mineral veins.

It is scarcely necessary, in conclusion, to apologise for the frequent use of the common terms of the miners. In a paper of this kind, it is almost impossible to substitute others for them. In strictness, most of them are inaccurate, especially as applied to the shifts of veins; as they describe the apparent, and not the real change which has taken place: but whilst we comprehend what is intended by them, we may talk, and write, of veins being heaved, thrown up, thrown down, wrung up, cut out, &c., just as reasonably as we do of the rising, and setting, and course, of the sun.

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