RECORD: Darwin, C. R. Geological diary: Port Desire. (1.1834) CUL-DAR33.229-242 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed from the microfilm by Kees Rookmaaker, corrections and editing against the manuscript by John van Wyhe 7.2010. RN1

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Marginal notes are here integrated into the text.

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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.


229

1

1834 Jan: Port Desire. —

The creek, at the head of which a small river enters, is in the greater part bounded on each side by rounded massive hills of Porphyry. —

Behind these there is the great table land. of the modern formation. —

p. 12 — account denudation of Porphyry

The plain has an elevation from 200 to 300 feet. In some few cases the Porphyry rises higher. (a) Port Desire heights are 440; But generally it is only seen where the softer beds have been removed by alluvial action.

The common Porthyry, for instance behind the Fort, has a compact pale purple basis with few crystals of earthy feldspar. In several places it contains sufficient quartz. 1654. 1684, 1639, 1768 &c. At the higest hills, the Porphyry contains numerous almond shaped concretions of similar earthy feldspar. 1634. 1635
note Book
layers &c
[illeg] in layers
which affect a laminated structure. 1636 ... 1638 These varieties pass into each other, or forms beds one over the other. drousy crystals appen
When I first saw these masses of unstratified, crystalline rock, I thought they belonged to the oldest classes; from this reason I found much interest in some cliffs, some miles up the harbor where we see these same rocks superior to conglomerates & others of aqueous origin. — [indicated] left conch great

After passing over many hills of Porphyry, there is cliff of a common variety (1677) 1677 with earthy crystals of feldspar, lying over two rocks; (b) on a feldspathic rock with mica & a semi crystalline pink Porphyry (1678. 1679) 1678. same 1666. 1679 red early [illeg] decidedly constitution with feldspar.

Between the upper bed there were some masses of Pitchstone (1680) 1680. All these beds dipped, as

[annual] denudation of Porphery] added pencil.

note Book layers &c] added pencil.

[illeg] in layers] added pencil.

drusy crystals appear] added pencil.

indicated latt. conch. fract] added pencil.

same as 666] added pencil.

Red early bas be deciding perpition with feldspar] added pencil.

229 verso

(a) These are two hills a few miles from the anchorange & were measured by the Barometer

(b) The bed of Porphyry (1677) is continuous with the range of hills behind the Fort. —

230

2

1834 Jan Port Desire

nearly as I could judge, at an angle of 12° to the WNW. The rocks 1678 & 79. were arranged in those sort of lines or planes, which immediately brought conviction to my mind of their being an aqueous deposit. — They passed into each other both in nature & color & were in most places softer & coarser. There was a strong appearance of containing foreign fragments pebbles, as in such rocks as (1649) & (1767) opake & some glassy feldspar & veins of do. same 660: —

# Walking onwards nearly in the direction of the dip, there is another escarpement, (with same dip &c) the lower bed is of rock Porphyry, like 1677. (a) & the earthy rock, (9649) the nature of which I do not feel certain about; these pass into each other, such Porphyries as 1674 earthy rock, but decidedly porphyry & 1679 making it difficult to say where one begins & the other ends. — Above these are strata of hard white feldspathic rock. (1650 like pumice. 1681 like 668 earthy white band & a soft earthy matter 1650. 1681 resembling chalk, it contains particles of quartz, edges fusible in the blowpipe, would (1651 & 1675) 1651. 1675 would appear to be feldspathic uncrystallized.

These rocks, like the former, rather pass into each other than are separated into distinct beds. but the earthy one, in all cases is the superior one. — Again passing onwards, there is a 3d escarpement essentially of the same nature as the 2d. —

(b) [sketch]

1675 1681 1674 & 1649 A
1651 1650 [aka] rocks 1674 1649 1677 B
good poprhyry & with pebbles has [illeg] (pass into each other)
1677 1680 1678. 1679 C

Opak & semi glassy feldspar & veins of do] pencil insertion.

Pebbles] pencil insertion.

Same 660] pencil insertion.

Sketch is ink over pencil.

230 verso

(a) Perhaps little is as perfect as (1677) but more like 7[number under tape]

(b) The same puzzle, which I had in the Falklands occurred here, to explain a succession of dip to one point without anyiclinal line: it is not all probable that the beds at (B) dip under those of A. but rather one field broken up into parallel & similar ridges. —

1834 May

This must remain doubtful: it must be remembered that the dip is small. & the crests not far part. also there is no perfect similarity of the inferior relative position of beds in the three crests. — Especially when we see the section (J):

Globular Porphyry

Daubuisson Vol I. p. 3111

1 Aubuisson de Voisins 1819.

231

3

1834 Jan: Port Desire

To the northward of the above sections, there is an extensive line of cliffs, whose the strata of which dip not very regualrly to the NNW. —

It is difficult to describe them from the incessant alternations, passages, variations in the different rocks. — The lowest bed is far most generally a red semi Porphyry (a) more or less crystalline such as (1674). 1674 — Th Above this the mass of the cliff os composed of yellowish white feldspathic (1672 1673) 1672. 1673 sometimes earthy sometimes crystalline. — with these occur rocks like (1679). 1679 round grain of quartz — In color from the white to the red there are endless shades of pink; likewise in the middle of the pink rock there are circular patches of more than a yard in diameter, & broard bands of white. — This figuring of color is oftentimes highly fantastic. — Vide Fig: . —

A third & even more common rock. is the one already mentioned, of a soft earthy nature, showing clearly lines of deposition, & appearing to contain extraneous fragments. (1649 & 1767). 1649 pebbles. 1767. 661 observe breccia [illeg] good [illeg]

Twice, when examining the rock in situ, I felt convinced of the presence of fragments, subsequent inspection of the specimen has shaken this conviction.

Amongst these three the above sorts of rock, in two or three places there were large beds of conglomerate; the pebbles varied in size from a mans head to almost sand. — They consisted of varieties of highly crystalline porphyries, of a dark red color, & different from any I have seen in this neighbourhead. — When the pebbles are small the beds from the curved inclined in position clearly show the action of the general dip same as in the other beds

231 verso

(a) This porphyry occasionally occurs higher up. — above the other rocks in the cliffs. — V (F)

232A

[sketch]

Breath of white lines about one inch

165

[sketch is orange background with yellow stripes, watercolour. caption is in pencil, sketch lines also pencil]

232A verso [blank]

232

4

1834 Jan: Port Desire. —

rapid currents. — The position was low in the cliffs, the altitude of which cliffs is about 50 feet. — Amongst these rocks are layers of Porphyry so fine grained, as to resemble Jasper (1647. 1648) 1647. 1648 V [porcelan] rock — The upper part of the cliff is more generally composed of white hard earthy felfspathic (1668) 1668 rock; & that sort which resembles chalk (165), which is often coarser & the uppermost bed is so coarse & contains so much silex as to resemble a sandstone it is like rock (1683). but coarser. —

(a) On the other side of the leaf I will give the super-position of the rocks. as in several cases I observed them. it must not be supposed that the junctions were well defined as here represented. —

dikes I noticed three sorts of dykes traversing the beds in these cliffs. —

1st was vertical, sides parallel & straight; composed of the soft rock (1649) little pebbles, & cutting precisely a similar rock; sides not aletered; central part of dyke tinged red. — 3 or 4 feet broard, appeared like fissure filled up. — The two other dykes were vertical, but tortuous, could be traced for many yards 1670, being harder than the neighbouring rock. — It is composed of numerous crystals of quartz, earthy feldspar, mica. in red basis (. 1652 1671) 1652. 1671 no line porphyry: the abundance of quartz is curious in a dyke. — Coarse E & W; sides not altered. Width about 18 inches. — In a section like (G) it cut all the beds. excepting the earthy feldspar. like (1651) & bed like (1683). The dyke. appeared to thin out before reaching them, & not truncated or covered by them. —

232 verso

(a) [sketch]

D   E F G
1669 1667 1683 (like) 1674 1683 (like below but coarser
1647. 1648 1668 1668 1672. 1673 same as next below but coarser 1674
1649 (like)   1667 1674 (like) 1651 (like)
1652   1647 (like)   1674 (like)
    1666    
    1674 (like)    

The word like means that the rock, is like the number mentioned; in the other cases, the rock specimens actually were in the relation to each other here drawn. —

in section (F) 1674 was not the higest bed, but I forget to note, which were superior. —

233

5

1834 Jan: Port Desire

The third dyke is composed of much mica, quar feldspar crystals or quartz (?). 1670 it ran N & S; width about 2 feet. — a small one of same nature cut at right angles the 2d dyke. (a) —

I will now describe two other sections, where we have a superposition of rocks nearly similar to those described in the western cliffs. — slate NNE near the Fort, the Spaniards have made a quarry for the sake of building stone. — The beds dip at about an angle of 10° to the SSE;
sonorous conch fract light
the upper one is Poprhyry (1684) 1684, which further on in direction of dip becomes more compact (1690) 1690 like 84, but like Porphyry; but the upper part affect the laminated structure (1691) 1691. — (abound shaped concretions)

freestones These porphyries overlie a variety of earthy feldspathic rocks; which pass into each other so insensibly as to render all divisions impossible. —

The red porphyry changes into white (1682) 1682 & rests immediately on a free stone, (fibrous crystals of feldspar) abounding with ferruginous lines, these are generally horizontal sometimes waving, so as precisely to resemble a common sandstones with [illeg] water ferruginous lines. —

A section will best show the superposition, but it is not constant for 10 yards. — (1685 & 1686) 1685. 1686 from same block, used for building. 1687(1683) is abundant. with at numerous lines of deposition from them. —

[sketch]

H
distinctly 1684
1685. separated 1686
1687
1683 (like)
1688. 1689

Varieties (1788 1689) 1688. 1689, are often so soft & coarse. as to resemble earth. — I can feel no doubt that the rock (1683) is formed from aqueous deposition. —

At the North entrance of the harbor. there is great bed of rock. the paste of which resembles that of the purple porphyries; it resembles a

233 verso

(a) The external form of these 2 latter dykes resembles, those in Volcanic countries. the presence of so much quartz is starling to their igneous origin. —

1691. a curious rock

234

6

1834 Jan. Port Desire. —

pile of grape & musket balls, from globular concretions of a paler variety, projecting outwards, 1764. 1765 these are generally hollow & lined with small quartz crystals. (a) — This lies upon common porphyry with crystals of earthy feldspar (1766) 1766.

(J) 1764, 1765  
  1766 all the beds already separated
  1767  
  1768  

Beneath this is a bed of the earthy soft rock which appears to contain extraneous fragments (1767),
1767 also been 660 good porphyry opake & glassy
& this, lastly rest on a Porphyry with much quartz (1768) 1768 like 766. —

All these beds have same inclination.

If I had only seen the sections (C) (H) (J). where the porphyry is clearly seen separated from the inferior beds. I should have thought, that this rock had been melted & poured over ones of aqueous origin, & which latter [tametrus] rested on others of an similar Volcanic nature. — I might have thought such semi-crystallized rock as (1679. 1685) raising in the midst of the others rather ambiguous.

But when I see (section B) hard feldspathic rocks (1650) passing into an earthy substance with specks of quartz (1651). — also li porphyries like (1674) (& (1673) passing into a soft one (1649) with numerous planes of deposition. — When I see (1674) & 1647 occurring above, in the middle, & beneath, & passing into such as above. In which beds, there are conformable strata of conglomerates & others with lines of water deposition.
inducted less good possitive with fibre crystal
I must suspect that 1684, 1674, 1677, are here always of aqueous formation & if so; most certainly the whole of them. viz. speaking 1634 ... 1639 1634 to 1639, & 1654, 1764; 1765, &c &c. — To this most Wernerian doctrine the dykes, so much resembling in figure (b). Volcanic ones, often the greatest difficulty. — from the one thinning out above. — Are there not dykes or veins in quartz rocks?. —

also been 660 good porphyry opake & glassy] in margin, encircled, in pencil.

234 verso

(a) (1766) Has in plane. jasper appearance, with very few crystals. like (1647. 1648)

(b) 1834 Febr at Port Famine. I have seen veins of common calcareous & clay slate traversing common fossiliferous clay slate of same shape & structure. —

at end
[illeg] compare with Cordillera & state greatness of formation

235

7

1834 Jan: Port Desire

Behind the Fort, (V small chart.) (a) stretching from section (J) to (C), there is a band of Poprhyry hills. At (H) the beds dip to the SSE (or about); at A & C the end of chain to WNW; at (D, E, F) to NNW, this we may imagine to be on the northern side of the line of violence continued, although hills not upheaved, as at (H) the beds clearly dip from the chain. — This line of hills, probably first determined the depression of land forming the creek or narrow estuary. — The Hills perhaps run W by S & E by N. —

To conclude with the Poprhyry. at Guanaco island. there is a cellular variety with quartz (1644. 1645); near this there is a bed Pitchstone (1642. 1643); & an iron stone 1646. —
1644. 1645 1642. 1643 1646. — 1655. 1656 higher
A mile or two further up we have two varieties of Porphyry (1655. 1656). —

At the head of the creek, about 25 miles up, the Porphyry rises into nigh, & almost abrupt precipices with caverns & peaks; from its fine red colour is very picturesque. — Its nature varies much. curious (1657 & 1658) are the commonest where Bluish & reddish fragments are mingled together in concretions & vesicular with quartz crystals.
1657. 1658 round [illeg] true breccia yet porphyritic

In this rock 1659. 1660 there is a strong appearance of extraneous fragments being imbedded. of the reality I am doubtful. — the opake crystals becoming glassy

Judging from their mineralogical appearance & superposition, I should not think these Porphyries of very great antiquity. — other Porphyries existed before them. — Perhaps they hold a position (b) "secondary" in relation to the formation of this country. —

Tertiary. We will not turn to the great modern formation: to the north of the Fort & a little above the elevation of the Porphyry range, there is

235 verso

(a) [sketch]
N. Plain Two Hills N.Plains 290 to 300
440 feet high
Plain 240-250 ft
1 mile

(b) March

In Tierra del Fuego I believe there to be a conglomerate in the transition state: A C. Blanco there is a quartz resembling Falkland Isd; at N side of St George Gulf, where same Porphyry is found there also is quartz: If The W by S & E by N range of hills is pretty certain; if the stratification was more clear & in a corresponding direction ( it would be a strong alliance with the southern & northern transition rock: — I almost incline to this opinion although without organic remains it is only conjecture. —

sketch is in black ink, on tracing paper, with brown ink captions.

236

8

1834 Jan: Port Desire

a plain, which to the eye, appears perfectly level. — Its altitude above the sea. by three Barometrical measurements is 241 feet. V (a) On the north side of the two Hills (440 ft) of Porphyry, there is another plain which appears equally level. By two observations it is 49 feet higher than the southern one & from appears to have the same elevation with the country which runs up to Cape Blanco & into the interior. —

[calculation] 241 [+] 49 [=] 290

It is surprising to reflect that these plains, which are so level, should have been subject to a force so enormous, as to upheave them from the bottom of the sea. The two hills of Porphyry forms a point when the force has varied. — ?

From the sketches of the land in St Georges bay, this variation has there taken place to a great degree. — We see it at Port. St. Julians. —

All this subject is reconsidered on a set of notes on the subject

Whilst at St Josephs, I believe, the planes of original deposition were retain yet in their ancient inclination. — In the Pampas of St. Fe. I was convinced, that the sea must have subsided that such a district could never have been subject to violent forces. — it yet requires the presence of these abrupt changes in height & the remembrance of the horizon-like beds at Port. Praya in the Cape Verds to make me believe in the contrary. —

The plains, are traversed by numerous ravines where orginally the geological structure can be seen. — G The upper bed is entirely composed of gravel, it is about 30 or 40 feet thick, it resembles the gravel at the R. Negro, but is rather larger in size. — the rocks are in an immense

236 verso

(a)

Calculated by De la Beches 247  
Three observations 217 ? Plain north of Fort. —
on different days 252  

Elevation of plain North of Two Hills 299 — 247 give 52 difference between the two plains. —

Difference of Observation on another day, taking the South plain as the lower station, gives to the other 47 feet. — mean 49 ft. 6 inch

Having recalculated these; there must have been some mistake: Baily's tables:

in the figure
measurement of first plain.
Hence if we assume from 245 to 255° as height. —

247
261
245
253

Avery good measurement of high plain makes it 331 feet above the sea. — Another 318. — we will assume from 320 to 330 as its height: difference 75 feet: —

237

9

1834 Jan Port Desire

proportion porphyries. — of a dull red & green colours, they entirely differ from the present rock in the infrequency of crystals of earthy feldspar. There are present some of white quartz. — The variety of Porphyry pebble to be mentioned at Port Julians is common, but not to the extent at that place. — G

Beneath the gravel, there is a very soft. white stone fine-grained sandstone. 1662 — if indeed it deserves this name, it contains much aluminous matter, is often-time calcareous effervescing with acids. 1640 —

I believe (b) it is this bed, which further to the South, has given rise to the name Beachy Head, signifying a resemblance with the chalk cliffs of England. — Beneath this. there is a bed of a more clayey substance 1663. 1664; conchoidal fracture, witha yellowish or greenish tinge. — it decomposes more readily & into small angular fragments: it contains pl thin plates of transparent gypsum. — I could not see any traces of organic remains. —

A few miles to the South of the harbor, there is a cliff about 100 feet high; the lower 40 feet is a bed of yellowish sandy clay. which rests on a flat of Porphyry. — in this clay there are layers, especially in the lower part of the large oysters, & some Pectens; there are very many Turitellae & some large Arcae. 1625 ... 1632 — there were some other shells. but I had not a good opportunity of collecting them. (a) — It appears to be the same bed, as at St. Josephs & St. Fe. The upper calcareo-sandstone (1640) is also the same, as at the R. Chupat Lat: 43°20' & at New Bay. —

237 verso

(a) I omit to state; that half a mile inland there is the plain with its gravel calc-sandstone & clayey bed, beneath which (though not seeing the junction) comes the oyster bed, resting on the Porphyry

(b) This formation extends up at least 25 miles up to the Westward & probably far more distantly

238

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1834 Jan: Port Desire

G The upper part of these cliffs is gravel; we have therefore here the gravel immediately resting on the oyster bed; at the curious porphyry cliffs up the harbor, the gravel immediately rests on that rock; I had thought (b) that this gravel. has been replaced by subsequent alluvial action, after the denudation of the upper parts. — But since seeing at St. Julians the great irregularity in thickness of these beds & which I can only account for by removals taking place by the same or anterior currents, which brought the gravel. I presume all the gravel have to be of the same age.

In this modern formation (a) I could no where see any signs of violence. — Where the paps of Poprhyry were a few feet beneath or protruded a few feet above the level of the plain, there was no change in the continuity of its surface. — I infer from this, that the Porphyry & modern beds were lifted up together & without disturbing each other. —

There is an interesting circumstance, that on the surface of the gravel on both the 240 & 300 feet plains & in the valleys, there are very numerous Patellae & muscles. — These, certainly are the same species which now exist on the rocks of the sea coast. — The muscles yet partially retain their blue colour & the Patellae are curiously perfect. — They are more abundant in certain patches, but are very generally scattered about. — This is to me a certain proof, that these plains have been uplifted from the

238 verso

(a) Therefore I think the elevation of inclination given to the conglomerates are & porphyry beds of to be an entirely anterior date

(b) 1834 may
I here come to this conclusion. V. St. Julian. —

Although at Port St. Julian the superior white beds (unquestionably deposited before any alterattions of level did occur at rather different elevation; yet St. Cruz geology has proved. that these lower beds of gravel are entirely owing to succesive elevations of the country. —

239

11

1834 Jan: Port Desire

bottom of the ocean within a recent period. These shells at present seem to live on tide rocks; from which I suppose the more ancient ones over scattered about the plains were in their time, carried by the currents to the bottom of the then existing ocean. — V. Appendix

It is curious to observe, how the causes which produced the enormous gravel bed over so many miles of country ocean, appear completely to have destroyed its inhabitants, & thus subsequently to only to have allowed a few shells, which now exist, to be scattered over its bottom. —

It is the more curious, as it seems probable that no long period of time intervened between the existence of the great oyster & those shells which now are lying on the surface of the plains. — At Port St Julians I show, that the oyster bed & white Arg: beds alternate; ? also, at the same place, some reasons (V [blank]) for supposing the gravel & Ang. beds have no very different ages. — At the R. Negro (V. [blank]) I thought the same thing. — Perhaps there the existence of the oysters (& of course their organic remains) immediately followed by the period of the by the deposition of the gravel; was as I have not seen any shells in the gravel & only three coast species on its surface, & as I cannot believe the ocean would remain sterile for any great number of years, I must think it probable that not much time elapsed between the deposition of first Porphyrt pebble & the upheaval of the plain; & therefore between the existence of another race of organic beings, the

239 verso [blank]

240

12

1834 Jan: Port Desire

great oysters & Pectens &c & the first occurrence of those which now are living. —

The extreme sterility of these plains, which form the coast of Patagonia has often been described.

Salenas. May not it be attributed partly to the recent residence of the ocean on its surface. — The water, which is collected in springs & pools even in the Porphyry rock near the Fort is all more or less brackish; This no doubt arises from the water draining from the more elevated plain, in which there are some small salinas; the water in bottle (781 tin lathe) is of the worst kind (a), the better sort was drunk on board the Beagle. — May we consider this as resulting from the wasking of the marine deposits?. Chemical analysis of this & salt from the Salinas will be interesting. . —

In a muddy valley, I found a saline incrustation 1633 a phenomenon so often seen to the northward. —

Beds rest on flats of Prphyry. As might have been expected from the soft nature of the beds, & the original inequality of the plains, this ground has been much cut up & removed by alluvial action; but in some place for instance at the head of the creek, where a small river enters, which now only deposits the finest mud, the valley is cut through hard Porphyry rocks, to the depth of 1 to 200 feet. —

Valleys in Porphyry
100 to 200 ft deep
the sides are praecipitous & anrupt peaks are left standing in the centre; the branch gullies are equally deep & wild in one case I found one commencing with a precipice of 60 or 70 feet high. — these are

100 to 200 ft deep] pencil over other entries.

240 verso

(a) The saline nature of the water is probably owing to salts occurring in those beds, which contain Gypsum. as shown at S. Cruz

241

13

1834 Jan: Port Desire

appearance. one meets with in Volcanic countries, where valleys are formed by rents & cracks; But it is impossible to suppose, that within the time a muscle has retained its color, such rock should have been cut through by present causes. —

Would not a broken, rugged country, when covered by newer deposits in an ocean, yet retain over the old vallies or rents gentle depressions sufficient however to determine the formation direction of the new vallies when, by the upheaval of the bottom, they must occur? — By this means I can alone explain the valleys which now conduct water in the Porphyry rocks. —

It may even be doubted how far the short period & dry climate is suficient to explain the denudations in the soft, modern formation. — It is well to know, that at Port St. Julian. the gravel & Arg: beds were cut through (a) by a mass of detritus with Mastodons bones, which must have taken place before the upheaval of the country. —

Porphyry. Sailing to the South to Port St Julians, at sea Bear Bay there is much rock, which in its external form resembles that of Port Desire.

Between this & Watchmans Cape, but very little of the downs or modern formation is to be seen. — At Watchmans Cape, some miles in the interior there are two little bits of table land & a cone, & no more now remains

241 verso

(a) The much greater alluvial action & consequent irregularity in outline in these beds this what is seen further northward in the Pampas, may be explained by following circumstances. — From more nearness to the Andes causing a greater irregularity in the elevating force, perhaps greater number of elevations exposing more lines to action of the coast; greater alluvial action from the weather, & lastly perhaps a less regular bottom in the old sea. —

242

14

1834 Jan: Port Desire to St. Julian

of the great plain, which doubtless once extended the whole length of the coast. — Here then are some large salinas, sealing vessels come here to take it in. — to the Suth of Watchmans Cape there are extensive flats & outlying rocks, which resemble those at the foot of the cliffs. South of the Harbor of Port Desire. — At Cape Look-out same form of rock. — all probably Porphyries. —

In Lat: 48° 56 the rock at coast, was Porphyry 1711 with much quartz & earthy & crystallized Feldspar.

The plain has an elevation from angular measurement of 350 feet; There was the bed of white soft fine grained sandstone, slightly effervescing with acids, which showed as at Port Desire in white patches on the sides of the Hills. — tertiary

To the South of this, the plain exhibted marks of great alluvial action, its outline resembling fortifications. — We then come to Port St Julian, easily recognized by the truncated cone of Woods Mount. —


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