RECORD: Darwin, C. R. Geological diary: St. Helena. (7.1836) CUL-DAR38.920-935 Transcribed by Guido Chiesura and Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)
REVISION HISTORY: Transcribed by Guido Chiesura and Kees Rookmaaker, corrected and edited by John van Wyhe 8-9.2011. RN2
NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Where pencil was used instead this is noted in the textual notes. Marginal notes are here integrated into the text. See the Beagle diary pp. 740-746.
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Reproduced with the permission of the Syndics of Cambridge University Library and William Huxley Darwin.
See the introduction to the Geological Diary by Gordon Chancellor.
The Beagle only staid five days at St. Helena, in this limited time I endeavoured to make out the structure of this Isd. which is so very remarkable as being a centre of distinct creation (a). I have however
but in succeeded but in a very partial manner. The mineralogical nature of the rocks, which in several respects are well worthy of being examined, I was necessarily compelled to neglect. The work of Mr R. Seale,1 the well—known naturalist of St. Helena will far better supply the place of my own observations.
See Daubuisson on p. 540, vol. II2 to prove peaks of passolite characteristic forms.
The coast in the greater part of the circuit of the Isl.d is formed by high & great masses of black, thinly stratified rocks. These in the few parts, where I examined them were heavy irregularly & highly vesicular, when otherwise heavy & of a dark colour. consult Lesson.4 They either consist of Trachyte (3701) 3701, or of dark Feldpathic rock, with a few embedded crystals (3700) 3700, or of Basalts with crystals of Augite & Olivine (3702) 3702. — They are but slightly amygdaloid. The strata are separated from each other, either by scoriaceous masses or by strata, varying in thickness from a few inches to two or three feet, of a brick red, loose saliferous volcanic sandstone. — This sometimes shows water—lines & a concretionary structure; but I feel quite uncertain whether is a subaqueous deposit. From the extremely porous state of the lava, it is manifest, it has not been coated under any high degree of pressure. —
von Buch p. 2943 Account of limestone deposited by spray
Von Buch has described a compact limestone at Lanzarote, which seems perfectly to resemble the stalagmitic deposition just mentioned: it coats pebbles, and in parts is finely oolitic: it forms a far-extended layer, from one inch to two or three feet in thickness, and it occurs at the height of 800 feet above the sea, but only on that side of the island exposed to the violent north-western winds. Von Buch remarks, that it is not found in hollows, but only on the unbroken and inclined surfaces of the mountain. He believes, that it has been deposited by the spray which is borne over the whole island by these violent winds. It appears, however, to me much more probable that it has been formed, as at St. Helena, by the percolation of water through finely comminuted shells: for when sand is blown on a much exposed coast, it always tends to accumulate on broad, even surfaces, which offer a uniform resistance to the winds.
saliferous] pencil insertion
von Buch p. 294 Account of limestone deposited by spray] in pencil
(a) I must also add how much I am indebted to the work of that gentleman, for the localities of every interesting feature in the geology of the Island. —
Some tufas contain ؟ lavas ?
& state at the time I entertained no doubt but since have many
from veins like appearance of decomposed feldpar. — Mere cones of doubt, as at Tahiti. — Compact smooth cut corals keep fine grained. Waxes as
that polish when rubbed into hand
The strata seem to have with some irregularities & a few exceptions, a general quaquâ versal dip, at a small angle from the central parts of the Island. — Rocks belonging to this series are best seen on the Northern side (a). — In two sections which I examined, these dark coloured lavas reposed either on an amygdaloidal scoriaceous mass, or on lavas, which appeared to have been of submarine origin. — These sections will presently be described. — The central & more elevated parts of the Isl.d are occupied by a very singular assemblage of rocks.— At first they appear like alternating bands of purple, red, white, yellow, & brown clays; on a closer inspection many of the latter three colours certainly are decomposed feldspathic lavas (3710 . 3711) 3710: 11, others probably are tufas (3712:13) 3712; 13; of the purples, some at least may be seen to originate in a clay-stone Porphyry, yet retaining its crystals of decomposed feldspar (3705) 3705, others, as before, probably are tufas (3706) 3706: of the red, the greater number of the strata have a brecciated structure & although now in the state of clay, have once existed as ashes or scoriae
in cinders. The very extraordinary degree to which decomposition has been carried on, is well worthy of a minute description. I regretted much that I had
(a). As far as I saw The coast is so formed, whole length from between Man & Horse & Horse pasture, whole neighbourhead of the town to the base of Sugar loaf & part of Flagstaff.—
Interval of the most inferior rocks: then the Barn: interval of the upper series. — Then Prosperous Bay Flagstaff: interval of upper series: Great Stony Top. nature not certainly known. — South Barn (E of Sandy Bay) so formed as in the extreme SW part of Isd (bearing taken from high peak) —
N.B. The same coloured strata cannot be traced continuously from any great length, whether owing to faults or to change of mineralogical nature I am unable to say.
N.B. I was reminded of the appearance of the mountains of Uspallata. —
not time to procure a series of specimens of the rocks, from their most earthy, into their stony forms. The coloured beds arise, at nearly an equal height, from the base of the most elevated ridge (which probably formed part of the crater) & thence slope uniformly downward to the sea. In parts they abut against the black rocks of the coast, in others, passing between & over them, they form lofty cliffs overlapping the sea shore. so that alternating modern series & older. Rocks of this series occupy much of the Eastern best pasturage & all the central part of the Island. —
Subsequently to this later accumulation of lavas & tufas, the strata both of this series & of the older one near the coast have been, in certain parts violently dislocated & in others, injected with great masses of igneous rocks [illeg] dykes. To this cause must be attributed the extreme confusion, which at first appears to involve the geology of the Island. — Having given this sketch of what appears to be the general structure of the land, I will now detail the principal parts on which these opinions are grounded. —
(a) on the west side however they appear to cap Man & Horse & Horse Pasture; they cover whole country; from west of ridge of Alarm House. across Rupert valley to Flagstaff; then on coast from the Barn to behind Prosperous Flagstaff. on the coast again as far as Stony top. – then unknown but seen on Long Range. & capping on inner side of south Barn. —
The Barn & Flagstaff hills form two of the most prominent features in the Northern parts of the Isld. The Barn consists of a great square mass, which belong to the first described series, as its name expresses, of thinly stratified, black, lava. — The strata dip at a considerable angle to seaward or about NE; hence the sea face is entirely so constituted but on the inland side, a thickness of perhaps 800 or 1000 feet of such lavas may be seen to rest on a pale coloured, decomposing mass of rocks. in which no structure is very clear. Both are traversed by an infinity of dikes. — The neighbouring hill, called the Flagstaff, has a quite different, smooth conical form, & from its variously coloured, highly decomposed constituent parts at once appears
[illeg] attached to the second series of volcanic rocks. — These consist of much white & pale brown wackes & soft tufas; decomposing purple Porphyries: & chiefly a dull red brecciated mass, which clearly owes its origin to small cindery fragment, now reduced & condensed into an indurated clay. — The whole hill is traversed by numerous dikes composed of various rocks & commonly of which many abounding of crystals of Augite which preserve a remarkable degree of parallelism in a NNW & SSE direction. (a). Around the entire inland base of this hill, which runs to a considerable height a sloping platform of the coloured rocks extend.— From this cause & the numerous dikes
(a) They are composed of various rocks & commonly abound with Augite
I at first looked at this point, as the eruptive origin of the whole. — At the time however I noticed, that towards the central & southern parts of the Island the platform rises to as great an elevation, & I afterward found there was another explanation for the
greater elevation for the structure of the [illeg] hill. — It is The Barn & the Flagstaff are united together by a knife-edged ridge, which from the sea, or any distant point may be seen to be of a different constitution from the upper half of the hills on either side. — It consists of thin beds of various kinds of lava in a rubbly, decomposing state: some are Augitic, others pale coloured & laminated, much is of a dull [slaty] colour, porphyritic or scoriaceous. & highly amygdaloidal.
These streams are
either separated by, so from each other, either by mere seams or by more cellular varieties or by layers of laminated volcanic sandstone, which in some places contains distinct rounded fragments. — In these [illeg] less compact to intervening layers, the interstices are filled up with gypsum & salt, from the latter cause, all the water which flows through any part of these rocks becomes saline. — It is probable, that the vertical layers of gypsum mentioned by Mr Seale occur in this series. — The appearance of the mass induces me to believe that it is of submarine origin but my examination of it was very partial. — (Where was has corals been discovered?)
924 verso [blank]
By Lieut. Wright's map. It is less than 3/4 of mile & curved
The ridge is perhaps half a mile long; throughout, the strata are inclined at a very high angle. from about 60° to vertical. — It was a considerable time, before I was convinced of this fact, owing to the multiplicity of the vertical dikes, which running NNW & SSE (as in the Flagstaff hill) & parallel to the direction of the strata. have caused a most singularly perplexing structure. — The strata being nearly vertical, the dikes
intertwining have a general tendency to follow up the softer less resisting layers; intertwining from one to the other, when they run for some distance in contact with a bed of lava, they can hardly be distinguished from it, & again when branching off, they cause the deceptive appearance of a bifurcating dike. — It was only by searching for a point of view, at the extreme basset edge (on the Barn) where I could certainly observe the parallelism & close contact of the whole great mass of strata. —
I may observe with respect to these dikes, that the greater number were coated, to the thickness of about a tenth of an inch with a jet black glossy mineral (3715 pitchstone ?) 3715: it is in these series, where a mine apparently following the course of a dike, has been worked for a fine red & yellow Jasper. —
The strata dip to WSW, & on that end of the ridge pass beneath & form the base of the Flagstaff hill.
925 verso [blank]
The upper part of which, consisting of the highly coloured masses, have an obscure stratification directed, at a rather less angle, towards a similar point. — When standing on the hill, this structure is not apparent.
opposite other end of the ridge, where the strata are most inclined, their basset edges, come in contact with the great black capping of the Barn, the beds of which dip, at an angle of 30° or 40° to a nearly opposite point. Here there is an anticlinal line of great violence. —
The mass on which I stated, the black lavas of the Barn repose, is part of the same with this ridge, but in it no stratification is visible, this must be partly owing to the violence it has there undergone, but chiefly from the
point of extraordinary number of the dikes. This remark is applicable to a considerable tract, in which the deep valley of Turk's Cap Bay & its branches, have been largely excavated. —
It becomes absolutely difficult to discover, through what substances the dikes have been injected; the greater number are brecciated as before, N & S, but others in all lines. — The appearance may be compared to those irregular spider's
webs, which coat newly turned up ground.
The junction of the ridge & Barn has been called an anticlinal line; this is scarcely correct, for at the distance of less than a mile
or two to the south, the beds of the upper series, stretch across the country in a horizontal position.
Moreover, at the southern base of the Flagstaff hill, the lower strata, instead of as on the ridge dipping to WSW, dip to the northward of West. ! ridge a mile long! The dislocation has proceeded from a point of disturbance, which however probably had a longer axis, directed in the line of the many parallel dikes. — Basaltic mass because augitic crystals. I may remark with respect to the age of the dikes that as such
are generally in most volcanic countries are nearly vertical, in this case, their injection must date must have been by that time was probably posterior to, but probably connected with the fracture & elevation of the strata. — In endeavouring to account for the origin of this disturbance, if we look to other parts of the Island, we shall probably perhaps discover the cause. At Little Stony Top, a rounded conical hill raises rather abruptly out of a gently sloping range of the coloured upper series. This hill is seen even from a distance to have a massive
Bearing SSW from the basset end of Barn
triangular axis, composed of a dark coloured unstratified rock. — On each side the coloured matter rises up, from the horizontal strata below, nearly to the summit.
From the decomposed strata of these rocks no
inclined stratification is visible at a distance, but it is almost evident such must exist, with a high inclination. The summit itself is composed of a small point of the hard internal cone or axis, & hence the name of Stony Top has been given. —
In the western division of the Isd the elevated & rounded-conical hill, called High Hill, appears to be similarly constituted, but the surrounding volcanic strata are not seen in close contact. Facts of a similar tendency, will be more minutely described, when we come to the description of Sandy Bay. Hence I suppose, a similar great open conical mass of some igneous rock has been protruded in a !؟ spot directly beneath Flagstaff Hill & the Barn. — As far as my experience goes, such occurrences in countries manifestly composed of volcanic matter, are far from common; we may imagine, that generally the fluid stone has found an exit, thus the expansive force has been relieved without disturbing the position of the strata. —
[sketch in margin]
In the above locality of the Barn & Flagstaff has been described as the remains of a crater; if my views are correct, this cannot be the case, but the opinion must be owing to the disturbance & to the great degradation of the strata & to the multiplicity of the dikes. —
I will now describe the structure of the next great headland on the coast a few
2 miles ? miles to the South; & will subsequently review the relative position of the rocks of the different series in this part of the Island. — 2 & 1/2 mile south of middle of sea or W E. end of Barn
Prosperous Bay Flagstaff hill, consist of a lofty mass of strata dipping to seaward or to about SE.— at an angle of 20° or 30°: the upper part consists of black lava, some of the streams being divided from each other by brick red layers. — For its grand crater dip ought to have more Easterly
It's appearance resembles that of the Barn & the as,
before at first stated, that of the greater part of the circumference of the Isld.— The lower part half, partly consists of thin beds, in a partially decayed state a more decomposed of Augitic & Porphyritic lavas, separated from each other by amygdaloidal beds. — In another. and partly of an unstratified mass of reddish coloured fragments, which must one time have been loose [rapilli] but now are cemented together & highly amygdaloidal. — This portion is traversed by an infinity of serpentine slighly tortuous dikes, the greater part of which have a N & S direction.
Besides these dikes, the mass has been rent by great irregular fissures & cavities, which are now filled up by a whitish breccia containing masses of the ordinary red kind, large fragments of the dikes & other
stony degraded matter. —
Presumption of [illeg] by
before horizontal covering
From some of their wider fissures, small veins branch off, in one of which
only alone I perceived in one spot traces of [illeg] [illeg] horizontal deposition. — This scoriaceous mass & the thin lava streams certainly composed to those which underlie the Barn & form the “ridge”. — In the space of coast, between these latter localities & Prosperous Hill & again a short distance to the south of it or from this latter place & likewise for a short distance to the south of it, the same irregular looking mass may be seen forming the shores. —
The whole of this is deeply covered by streams of more modern lava, which form a lofty cliff & worn into the valley on the coast; — viewed from a vessel at sea, they appear horizontal, but in truth they
decline slope gently towards that direction. — On one side they approach rather less than half mile close to the inclined strata of the Barn & on the other, overlap & wind round the inland side of Prosperous Hill. — This space must have originally existed as one great internal measure two miles valley, it now has been worn into several, namely (2) Gregonas, (1) Turk Cap Bay
& again form cliff to S. overlies northerly formation
& Prosperous Valleys. — As I have said, winding round the black capping of & inclined strata of Prosperous Hill, to the South of it, they cover the same inferior mass & lastly come themselves down to the waters edge. — infra
The structure of the coast at great Stony top is unknown to me. — it appears as if there had there
been happened some unequal elevation. infra
strata streams between the Barn & Prosperous hill are composed of compact & commonly generally laminated lavas, some of which are white or pale brown with small crystals of glossy feldspar & then blackish green (3708:09) containing also a few of the same small crystals. of glossy feldpar. As far as I was enabled to judge these lavas passed under, & in some places overlay a part of the coloured strata of the upper series as these latter sloped downwards to the sea. — they are evidently conformable and [illeg] & of same nature
Can we believe that these
compact rocks, which are compact on the coast, from the greatly increased moisture of the interior, have been decomposed & produced the white layers of the upper series? If not so, we must believe that these lavas proceeding from a distinct source, have been interstratified with that series. — Some are stream of rather diff. composition
There are difficulties in both views; but however this may be, we see in this part of the Isd the an inferior mass
which probably is of subm capped by isolated hills of dark coloured lavas & the intervening spaces filled up with horizontal streams.
of a different
variety varieties. These were best seen near Prosperous Hill; are unconformably superimposed placed & therefore are of posterior origin.
With respect to the original position of the strata of the masses of older lava; — in the Barn, from the great dislocation which
in has so greatly elevated the strata in the Flagstaff hill, it is is scarcely possible to form any judgment; in Prosperous Hill both they & the inferior mass possessed a dip, anteriorly to the deluge of more recent lavas.
(a) High Knoll to S. Barn Basalt to Basalt due N & S 4 Miles — by about 8 or 9 long E & W, direction common to both craters. —
We also see in
whole the greater part of the circuit of the Isd the rocks of the first series with a dip to seaward. * —
giving irregularities slates dip round islds with modern lavas, [illeg]
* Prosperous Hill is one of the strongest exceptions. the dip being there SE (instead of ESE ?).
In the S. Barn
This structure & the removals of large portions, can I think be only understood on the supposition that formerly these black masses formed parts of one of those immense craters such as
yet now may be seen traced in the circular range of mountains in the Isle of France (a) or in Santorini &c &c . — In the former of these Islands, if eruptions or so of variously coloured lavas, were to take place from the Pitou du Milieu, on so a great a scale, as fill up the central plains & the spaces between the coast mountains, the original structure would very closely resemble (with the exception of the dislocation) that of St. Helena.—
NB. Whenever a deep section was presented the number of dikes was excessive & many of them of great size. — I should suppose (although it is a object likely to cause deception) that at least one perhaps more third of the mass was so constituted. Now would must not the effect of this be to increase by so much the limits of any old crater?
or the dikes are. May not this partly account for the so called craters of Elevation? — NO
[sketch] (b) (a)
(a) & (b) original limits
On this view. It would appear that that towards the SSW (near Sandy Bay) side of the Isld
NO] written over the preceeding paragraph
a very large portion must have been entirely removed; judging from the dip of the South Barn (SE by E 3); its form probably was an oval & its SW extremity must have extended
for over a considerable space now occupied by the sea.—
NB. Extremity of the Isd bearing from High Peak SW. possess a dip apparently directly from that peak
therefore due S.W.
3 It is most probable that this dip has been altered
We will now turn to the Southern & most elevated part of the Isld; — the source
from whence the upper series of lava have proceeded. — Commencing near Diana's Peak, a semicircular, or rather semioval ridge may be traced to some distance beyond High Peak. — Its length in a curved line 4 miles must be 4 or 5 (?) miles. — The elevation of the different points vary between 2000 & 2600 60 (?) ft.
The axis of more modern crater probably not coincident with ring of black
On the South or inner side, the ridge forms a steep
wall or slope wall or bank: on the outside, the sloping hills of coloured beds, divided by wide & deep valleys, rise from the sea cliffs (on the N. & Eastern sides) to the base of the narrow summit crest of the ridge.—
From Diana's P to High P. in St line nearly 2 & 1/2 m
Nest Lodge to Diana Peak in St 2 ¼ of mile
The ridge itself is composed either of a whitish greyish semidecomposed feldspathic lava (3710) containing minute black particles, sometimes reduced into slate of clay & sometimes highly vescicular (3707); or of a dull red (3707) brecciated, clayey mass which clearly has resulted from the decomposed scoriae. —
Feldspathic & after basaltic upon [feldspathic]
Normal cap on zenith
Posterior injected basalt
These soft grey lavas & red tufas
send off spurs & overlie the coloured beds, the nature of which, is but very slightly different. — The curved ridge in its outline consists of many smaller curvatures; in some parts there is a lower ledge, which imitates in form the upper crest; in such parts the constituent masses may be seen to dip outwards.
The highest part of the ridge is exceedingly narrow. — frequently presenting on each side a steep wall. — This last fact I observed in several craters in the Galapagos Isd.— From these facts & the general appearance, I conceive, there can be little doubt, but that we here see
part a remnant of the large crater, from which the upper series of lavas issued.
We shall afterwards show that in a whole archipelago the windward side has been removed
To this view, the structure of the Amphitheatre, included within the horns of the ridge (Sandy Bay valley & its branches) perfectly corresponds.
We see it a chaos of bare, waterworn hillocks & ridges, coloured red, yellow, brown: — the chief part consists of red decayed scoriae, mingled with yellow clays full of broken crystals, those of Augite being particularly large. — Here & there occur masses of highly cellular or amygdaloidal lavas. — The
whole is interlaced with numerous dikes. Not far from the centre, a remarkable hill, called Lott, rises through one of the internal ridges. — 1444 Its form is irregularly conical & pointed; its diameter, at the lowest part visible, cannot much exceed its height; — Which perhaps is between 2-300 ft. Its structure is remarkable, the lower part being laminated in large curves, some parts angulo-concretionary, & on one side there is a distinct columnar structure, radiating outwards from a central point. — The soft rubbly strata, on the two sides where alone such are visible, dip
away at a considerable with a very decided inclination.—
This great cone of rock is composed of a greenish-grey Phonolite (?), abounding with minute acicular crystals of glossy feldspar : (3703) its fracture is conchoidal & when struck is sonorous. — In a SW direction there are several other very remarkable but not so regular pinnacles (Lott's wife & daughters): These are evidently connected on a line of great dike, a fact which their flattened forms & position would close betray.—
I suspect the lofty peaks, called Man of Wars Roost* & Lott himself all belong
Asses ears ?
to one, not quite regular, line. — It is certain that three or four grand dikes, may be
traced seen, for a space of two or three miles, running in a parallel NE & SW lines with which several great masses of igneous rocks are connected. This NE & SW direction. was probably common to the longer axis of the crater as it is at present to the Island. —
parallel to longer axis of imagined crater
No E & W inland (?)
There are however hills, connected with dikes, independent of this line, and these other hills, which appear altogether isolated. These if not surrounded by
such so elevated a ridge, & especially if their bases, were more thoroughly cleared of the [ torn] loose cellular rocks, might be called mountains. —
Two of them, which I examined, were composed of a greenstone-like base with crystals (not elongated) of glossy feldspar (3704) 3704. —
From facts which have been already described, it is seen that these injected conical masses are not peculiar to within the
internal limits of the crater. —
From the similarity of form of Lott,
to although on a smaller scale, to those remarkable peaks of Phonolite, which are found in various parts of the world, I may instance that of Fernando Noronha; I believed I here saw a general explanation of the manner & of the
model, in which, they have been cast. I may remark, that these cones of hard rock would in most cases long survive the entire removal of the surrounding softer strata. —
NB. Dr Daubeny P. 37 has given a similar opinion with respect to Basaltic hills in the Velay. —1
With respect to the condition of the crater, when in its former state of activity I
to can only remark that very high up, & on the external slope, in sections made by the roads, the white lavas in many places overlie an undulating & water worn surface of red brecciated tufa.
؟ Find of ejection of what
Which relation then of age does old cones bear to [illeg] subsequent, if those old more [illeg]
In one spot a vertical dike, about 4 ft: wide cut through this latter substance, & being abruptly truncated by one of the
curved undulations was covered by the feldspathic lava; about an inch thickness of red earthy matter being spread only interposed. From this fact the inferior mass must have been exposed during a long period to degrading causes, before the extinction of the Volcano.
So conceal even the modern crater !!!
Does this belong to old series? I much suspect section occurred W. of [illeg]
Did Must Have not such causes most probably have acted on the surface of the land & not beneath the waters of the sea? — At the present time, it is not possible to trace the entire limits of the crater; respecting the northern border (?) V. Model I feel little doubts, but a larger portion then the half, has on the S & SW sides been completely obliterated & removed. Supra.
S & SW sides are to windward & exposed to far most swell
Near to the sea, at Sandy Bay, an obscure dip to seaward is distinguishable, which
1 Daubeny 1826, pp. 37-8:
the basaltic rocks of this neighbourhood are of very different ages, though I cannot admit that we are justified in estimating their relative antiquity by comparing together the depth to which the several parts of this formation have been worn away. M. Bertrand Roux himself furnishes us in my opinion with a convincing proof that the effect has not been dependant on the longer or shorter continuance of causes now in action, when he mentions that the rock on either side of the old Roman roads, none of which can be less than 1300 years old, has undergone since that period scarcely any sensible decay. Instead therefore of considering with M. Roux the amount of the destruction that has taken place in different parts of the formation, a sort of chronometer to assist us to determining their relative age, I should rather adopt the converse of the proposition, and argue that the time required would, according to his own shewing, have been so immense, that we are in a manner driven to suppose the effect to have been brought about by causes differing in their mode of action from those at present in operation.
The conclusion arrived at by either process of reasoning corresponds, however, in assigning to the volcanic products alluded to a very remote antiquity; for whilst M. Bertrand Roux is bound to suppose them as much older than the Roman roads, as the whole amount of the degradation they have experienced exceeds that which has taken place since the date of the latter; my conclusion leads me to place their formation at an epoch at least somewhat more remote than that of the last general revolution which has affected the face of our planet.
may perhaps indicate the former basal parts. Its figure was probably oval & of large dimensions. —
The least internal diameter in longer axes 2.1/2 miles. —
As, according to my view, this crater was formed within & on the Southern W sides of the ring of a more ancient crater; & as, the interior one has lost so large a part of its circumference, we can feel no surprise, that the black rocks of the older series do not at all appear on the SSW & most incomplete part of the Isd. —
In attempting to consider the age & manner of elevation of the land, we will first describe some patches of calcareous sand, which occur both on the Northern & Southern sides. — In both localities, the sand is agglutinated into a soft sandstone; which from that
same cause texture is obliged to be blasted with gunpowder; for if obtained otherwise, as by a pickaxe, it would all crumble away with loose sand matter. — The sand consists of minute well rounded particles of volcanic rocks & crystals, mingled with a larger proportion of the other white & calcareous ones. — These in their forms, lustre & colour (some few even being pink) strictly resemble the much worn atoms fragments of shells & corals. — I confess however that in few or none could any trace of organic structure be perceived. — Speaking
3) We here obtain evidence of another distinct step, without we suppose it is contemporous with black rock of the coast, under which view the side of black rock cannot be seen in the light of a crater in the [illeg] [elevation] & this explains [what] I shall suggest for these
[irregular] sides of rock with irregular quaquâversal dip. I shall give in my Chapter on the C. de Verde Isds.
The least...2.1/2 miles. —] pencil in margin
3) We... Verde Isds.] pencil in margin
I believe much some of the sand in the Keeling Isds (Lagoon Isds) was in this state. In general aspect the sand on some of the beaches on Galapagos Islds was precisely similar.
NB. At Ascension in the hard calcareous sandstone scarcely a trace of organic structure could be perceived. These beds differ from those of Ascension in greater fineness, larger proportion of volcanic dust & complete absence of all large fragments of shells, all which agree with the idea of [winnowing]. The pink coloured particles of Lime could only be so coloured by organic bodies.
at Sandy Bay the soft ordinary sandstone (3716) is in a few parts cemented, by the blending of the calcareous matter into a hard compact with semi-conchoidal fracture, rock (3717). —
Sandy Bay 70 per cent of lime
James Valley 54
Beatson p. XXII1
In the gullies which descend from these beds the stones become coated with stalactiform limestone (3718).— These are peeled by the workmen & the coating alone affords pure lime; some however of the sand contains but a small proportion of volcanic particles; whilst that from the Sugar Loaf quarry, after being burnt, does not require the addition of sand to make mortar.
At this latter place, some of the stone is almost constituted of minute atoms of a delicate land shell; (3720); besides which there are a few layers of angular small fragments of rocks & nearly perfect shells of Succinea (?) & Helix (species now living, 3729): In this part there are also the bones of small birds; & I believe it was here, or in one of these quarries, that an egg was found buried at a depth of 14 ft. — Close to the part abounding with the comminuted land shells, the ordinary sandstone (3719) is also found.
We may imagine that in the first case, the sea sand was left for considerable time
1 Beatson 1816, p. xxii:
There is moreover a very extensive quarry of pozzolana on the eastern side of James's valley, about a mile from the sea. In the year 1807, my predecessor, Governor Patton, to whose talents and indefatigable exertions the island is much indebted, first introduced this valuable ingredient in mortar cements. It was pointed out to his notice by M. Joinville, who had been attached to the suite of the Honourable Frederick North at Ceylon. This pozzolana, mixed with one-third of Sandy Bay lime, hardens in sea-water, and has withstood the beating of the waves for several years without being in the least degree diminished or affected. Even when used without any admixture of lime, or water, but merely after spreading it dry, and beating it well together, it soon consolidates after being moistened with rain into a mass almost resembling stone. In some parts of James's Town it has been used as a substitute for paving, and has been found to answer that purpose, not being liable to crack; nor is it in the least affected by the heaviest wheel carriages.
James's Valley is listed in a table on p. xxiii as 54 parts of "calcereous Earth".
NB. At Ascension...organic bodies.] pencil in margin
loose dry & unconsolidated. — In the mass of earthy detritus, which partially caps the calcareous sand, there was some gypseous matter, which occurred much in the same manner, as water, which having oozed into the ground is there frozen .— Mem. Ascension. X On the side of the hill, adjoining to the quarry, many of the fr fragments of rocks were white-washed 3721: 22: 23 & others thickly coated with a pale brown earthy limestone. (like tosca) — Some of the nodules were more singular, a more an earthy white calcareous centre, being in a similar manner enveloped. —
I suppose this process must be owing to a gradual solution of the lime
from in the sand & its redeposition by the action of the rains. But I may mention that at the Mauritius a rugged field of lava was in a circumscribed space coated with a similar limestone & which I saw no other way of accounting for than by the supposition of a former calcareous spring having existed on the spot. — Many others in very large quantities (R. Seale)
[illeg] beds have a general thickness between two & three, to fifteen feet. — they are divided into numerous thin layers which are conformable to the surface on which they happen to lie, & hence generally are highly inclined. — The beds coat the lowest sides of the hill at the head of little gullies & in the places which I saw were similarly in
situations, which evidently would be occupied by sand blown up the ravines by prevailing wind. — Such I feel no doubt has been their origin; but it is very remarkable that at the present day no white sand is found on any of the beaches. — Moreover the calcareous sandstone occurs at elevations of some hundred (3 to 600 ?) feet above the level of the sea: & in a quarry near the Sugar Loaf, with the present form of land, sand could not be blown up from the beach.
The quarry on the windward side is situated close to the brink of a great 650 ft perpendicular wall, & on the other & leeward side, the gully descends by a circuitous course, in which none of the Limestone is found. — Hence I am induced to believe that at a period where the land stood at a lower level, the coast abounded with a larger number of shells or corals (owing to
[illeg] a greater quantity of calcareous matter ?) & that the winds, winnowing the smaller & lighter particles, blew them into their present position. & the water percolating has coated surface of rocks & stones.
[sketch] When sloping Coast like Ascension
On the sea coast I did not see any signs of recent elevation; but the form of the land behind Prosperous Bay Flagstaff Hill, taking the S. American coast as my guide, would indicate the former residence of an former ocean. Superficial bays have been hollowed out of the upper horizontal strata within which, flat topped points stand isolated.— A structure, which it is difficult to imagine the
action of the weather could produce. The elevation of this place, must I should think, be at least 1000 ft. —
give reference of page
In a narrow valley, which leads up from Prosperous bay beach there is an accumulation of sand, muddy clay, coarse & fine angular fragments of rock, alternating together to a thickness of about 100 ft. — It is remarkable from the discovery by Mr Seale of bones of birds, which do not now haunt the neighbouring precipices. — I was not so fortunate as to find any. —
NB. My guide said he had often seen the tropic bird there alive
The mass of detritus, judging from its appearance, would be though to be an accumulation formed under existing circumstances. — It is however strange that the stream should now wear a narrow gorge, through the matter which it had previously deposited. — I believe such depositions are not common in the other valleys, otherwise I should have suspected it was a marine deposit. (of which on the coasts of S. America some cannot be distinguished from Alluvium) when the sea occupied the valley. —
Mr Seale curious case of ravines wider at bottom.
Guided by information from Mr Seale I searched the sea-side of Flagstaff Hill to discover certain shells, supposed to be of marine origin, & found at considerable elevations. That the movement must have been long ago form of cliffs will show. — subsidence. The rains acting
on the soft rocks of this hill, bring down large quantities of earth & small stony fragments, the whole stained black by vegetable matter. Beneath such an accumulation of about twenty feet thickness, the lower one or two yards
or three feet resting on the volcanic tufa contained scattered fragments of shells; one larger was slightly hardened apparently by calcareous matter & was full of shells.— Amongst them far the most abundant kind was a large appeared to me to be allied to Bulimus; there were delicate fragments which appeared to belong to young individuals. — 3725. 3726. Shells occur upon flats, in one instance upon plain R. [illeg] (state size &c) the rim & a sphaerical egg, very similar to some, which I have seen of a Brazilian Bulimus. —
These were associated with an elongated * (* extinct ??) land shell & the remnant of a flat Helix (3727). — (3727). Mr Seale most kindly presented me with a parcel of shells which he had sent a man to collect on Flagstaff hill, at a spot elevated 1737 ft above the sea. — These shells were all perfect & had been picked with care out of a black mould. — In general form they resemble my Bulimus but differ from it in possessing a very thickly incressated lip; in examining the specimens I see (3728)
N.B. Mr Seal's shells appear more elongated, some few are less so than mine; that is on the supposition of the thick lip
having being removed
this is a character which varies; moreover, in those I collected the margin in some is broken, but in one specimen the traces of the thick lip are sufficiently clear. — I confess it is strange that all mine should be in this state; it must however be recollected that perhaps with those presented to me by Mr Seale such might have existed
in the earth, but from this same cause were not collected. — [Insert] on long time to breach basaltic masses
I believe it is a Land shell; but whatever it may be, there is no question, but what in this Isld it is an extinct species. — State normal condition [illeg] trachytic peak but hill higher than basalt
I have stated my reasons for believing that the
most inferior lowest beds of lavas are of submarine origin; which also perhaps is the case with the [illeg] exterior ring of black volcanic rocks. — I have also conjectured that the second elevated & more modern crater was submer when in action raised above the level of the waters. — The former reasons receive some support from the patches of calcareous sandstone, & certain forms of the land. — But, whether we look at the low cliffs especially on the windward? side, which forms the circuit of the Isld. — the deep valleys, — the excessive decomposition of the rocks. — or at the demolished state of the craters, we see clear evidence of a high
Sum up — whole history
This rising would be also centre of [illeg]
Elevation of base broken most Flagstaff
consider decomposition. detritus wear & tear of crater
environs cliffs, most wonderful. — Grant that the first land islets most ancient shells & vegetation
subsidence — [E. hunters plants] shells. [map] flow &c &c
antiquity.— A conclusion in harmony with the extinct species of land shells & probably also with that most singular feature in the Natural history of St Helena, its unique Flora. —
theory of subsidence
Make note Governor Beatson mistake of [centre] primitive1
"Carmichael on Tristan de Acunha"2
Chimney on top crater [sketch] R.N. p. 433
R.N. p. 63: pitch stone dikes4 — Mackenzie5
On pebbles coated by lime p. 84 R N6
Earthquakes R.N. p. 1257
(Buckland on egg found in sandstone. Geolog. Transaction vol V. p 479).8
Von Buch Canary Isles p. 375 says limestone of St. Helena like that of Fuerte ventura of Lancerote. – Mem. his curious theory: of wind with spray !!!! – Von Buch. Basalt near James Town quantities of [illeg] [lava] & no crysts of glossy Feldspar!!!9
The amount of elevation ascertained proof of probability of external ring being submarine
1 Alexander Beatson (1759-1833) an officer in the Madras infantry of the East India Company and later governor of St. Helena 1808-1813. Beatson 1816.
3 Red notebook, p. 43.
4 Red notebook, p. 63:
At Vesuvius. Vol III P. 124. Lyell. dikes bave a parting of pitchstone; which is described as very rare. Mem. St Helena; probably more abundant in this case from intersecting a mass probably cold & not warm as sides of a crater as Vesuvius. —
6 Red notebook, p. 84:
State at St Helena. pebbles entirely coated with Tosca. which implies motion in the [loose] bed of pebbles. (On a sea beach under a cascade, one can understand pebbles thus coated. — The motion is most wonderful, from chemical attraction, as a blade of grass penetrating by action of Organic power a lump of hard clay —
7 Red notebook, p. 125: 'Earthquakes at St Helena. 1756. June 1780, Sept 21st. 1817. — p 371. Webster Antarctic veg:'
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