RECORD: Darwin, C. R. Geological diary: East Falkland Island. (3.1833) CUL-DAR32.123-132 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 against the manuscript and editing by John van Wyhe 7.2010. 11.2011. RN2

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. 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.


123

105 1833 March East Falkland Island 105 (1)

The only part of this island which I have visited is in the neighbourhead of Berkleys Sound a large piece of water which runs inland for about 15 miles in WNW direction. — On both sides it is bounded by low rounded hills the crests of which are of the naked rock, but sides covered with a sterile vegetation. — The rock of which these hills are composed is Quartz, which varies in its nature & purity. — The country which surrounds the end of the Sound is lower & more level. it is essentially formed of slate. — This lies between the two ranges of Quartz rock & is subordinate to it. — from containing organic remain it is preeminently interesting to the geologist. —

I will first describe the mineralogical nature of the quartz. & then of the slate. —

Quartz Rock

This when in its purest form is highly crystalline, yet & is found composed of in these courses largish grains; I do not imagine the grain were ever separated 1036, but that it owes this structure to a process of crystallization. The rock of which the whole range which borders the Sound & joins on to the slate is the same in structure, but contains in the interstices small portions of a white powder with which possesses a strong aluminous smell; this latter stratum varies much in quantity 1078. 1079, when abundant it forms gives rise to a singular mountain rock. — In one place the Quartz 1084 being in smaller grains assumed an rcenaceous appearance; in another besides the aluminous powder there were minute black imperfectly crystallized specks of a mineral which appeared to be mica

which possesses a] added pencil.

stratum] added pencil.

gives rise to] added pencil.

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1833 March E. Falkland Isd 106

(2)

these specks were arranged in planes & gave to the rock a slightly slaty laminated structure. — I imagined I here saw an abortive attempt to form Gneiss. — In a hill within one of the Quartz ranges. there was a quantity of rocks. which very strongly resembled closely constricting a Breccia: it was composed consisted of angular pieces of quartz imbedded in a compact. white hard base. Instead of being a Breccia 1080 1134 I imagine the aluminous matter has united with some of the siliceous to form the basis, whilst the pieces of quartz are of a concretionary or crystalline origin. K. Geog S. — The whole country to the north of Berkeleys Sound & generally to the south end is composed of the two first varieties of the above mentioned rocks. — stratification = form of land =

Transition

Where the alumino-quartz approaches the slate district 1081 it becomes more earthy & ferruginous in its nature: by degrees it passes into a pale coloured slate (1082), divided into fine laminae; although the change is so great. yet its steps are so gradual that it is impossible to fix upon any one spot. Specimen (1135) 1135 is perhaps as intermediate in its character, as any that could be found. the structure here partly changed from slightly inclined beds into nearly vertical laminae. —

Proceeding on a few yards we meet with slate (1082) & in a short time more perfectly formed sort (1083) 1083 slate. — These two last specimens well represent the general slate formation; — the more general colour is the pale one; it is fine grained & much divided by laminae

specks] added pencil.

gave to the rock] 'to' pencil.

K. Geog S.] added pencil.

& generally to the south end] added pencil.

stratification = form of land =] added pencil.

Transition] pencil in margin.

1083 slate] 'slate' pencil.

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1833 March E. Falkland Isd. — 107

3

with smooth surfaces; the planes of cleavage (b) (c) are generally uneven or a little tortuous. — Only in this one place I found the regular transition (a0 from the quartz to the slate, but in other rocks which could neither be ranked in one or the other classes, so equally did they partake of the b characters of both. —
II

In one locality the slate was of a black colour & contained scales of mica. 1085 —

The slate has al planes of cleavage running whenever I examined them, in a direction of between (E & W) & (E by S & W by N). they are either vertical or dip to the opposite quarters N or S. at angle of 65° & upwards. —

In the above described formations, after observing the crystalline & nearly pure siliceous nature of the one & highly laminated structure of the slate, I had not the slightest expectation to find organic remains; — the whole appearance of the country has led me to suppose they belonged to that class. which does not bear the signs of the coexistence of living beings with its formation. I was therefore the more surprised to find near the settlement to find withinthe slate; beds of slaty sandstone — which abounded with t impressions & casts of shells. (b) — The sandstone is fine grained & soft; it is often slaty. in which case it generally contains scales of mica: the whole rock is banded with narrow stripes (or slight alterations in colour.) which are parallel to the planes of stratification. — The included organic remains

II] added pencil.

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(a) At the most East & northern & inland branch of St Salvados bay there occurs one of these transition rocks: it dips to S by E, 30°: near also was some quartz rock: also clay slate. with narrow imbedded stratum of sandstone. —

(b) From the above reasons I think this one of the oldest (or most inferior) formations which even is fossiliferous. — the general character of the organic remains would also lead to this conclusion; it will be therefire preeminently interesting to compare these fossils, with those of a similar epoch in Europe: to compare how far the actual species agree & the comparative number of individuals of each sort. —

(c) Mr Greenough supposes serpentine or tortuous cleavage owes its origin to unequal effects from Caloric. — the cleavage here is not sufficiently tortuous, otherwise it would be a good example. against Mr Greenough hypothesis. — Does not the Gorgonia & Encrinites indicate a hotter climate? —

1 Greenough 1819.

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1833 March E Falkland Island 108

4 (X)

are found in seams or beds between the sandstone strata. In some case the casts form the whole mass. in others they are imbeeded in sandstone, & very often in a matrix of hard blue compact rock. From 1089 ... to 1128 & 1152 — The shells all belong to Terebratula & its subgenera; there are also different species of Entrochites & some vestiges of some other remains. the nature of which I could not ascertain. 1045: 46 1903 ... 1909 — Gorgoniae 939 ... ... 46.

The beds of sandstone vary in thickness from two or three inches to as many feet: in one place there was an extensive bed of about 12 feet thick: almost universally they are covered In the above & below by the highly inclined laminae of slate which run in their unusual direction. — The sandstone rock, where organic remains are not present, breaks splinters at right angles to its stripes & natural planes of division. — This from its appearance is contrary. to what would have been expected & often rendered the obtaining of the fossils more difficult. — I am inclined to attribute this to the same principle which has given to the imbedding slate its vertical cleavage.

In one place I found within the laminae of clay-slate a few shells 1129 ... ... 1131, but it is evident during the formation of the rock. circumstances were not favourable to their growth: also from the thickness of the beds composed of impressions of large shells, there must have been considerable intervals of time. between the successive deposits of sandstone & that subsequently to these another

Many pencil additions and corrections to this page.

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1833 March E Falkland Island 109

5 (X)

great bed of clay-slate was formed. — Upon considering these facts it is the more remarkable to find both the superior & inferior slate with a cleavage possessing the same direction & high inclination; (the beds of interposed sandstone dipping at small angle to a different point) (X) it would point out some law which continues the same after intervals of time & changes of the surrounding circumstances. —

[No Cell Matter]

I applied Acid to the casts of shells. but did not perceive any effervescence. it is a curious subject of investigation to know what has become of the Carb: of Lime. — from the state of preservation in which the striae & processes about the hinges are in; they must have been involved in their stony matrix. in the place of their growth & probably when alive: What we now see, is the internal model or cast, & the impression of the outer parts of the shell, but the body of the shell itself seems to have been removed; we must however suppose it to have been present untill the surrounding mineral was consolidated; & then how did the shell constitutent parts of the shell escape? — & where did they go to? —

With respect to the position stratification of the sandstone strata. in any one spot they are of easy & certain ascertainment. The seams of organic remains are parallel to the beds & from the flattened form of the shells it is manifest they would show the original plan of deposition.

[No Cell Matter]] pencil.

stratification] added pencil.

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1833 March E Falkland Isd. — 110 6

From the greater number of observations the strata dip to between SW & S. at angle at ∠ from 15°-20° — but in some places they were horizontal, then much twisted & again dipping at higher angle to N or N by E: also over to W by S & SSE: yet decidedly where the strata were most regular the SSW (or about it) dip was observable. —

The appearances are exactly what I should have supposed a bed of rock would have shown. which had been elevated from a great depth beneath the sea. —

30° - 40°

The quartz rock is divided into beds, which are from less to more than a foot in thickness. their general dip is at about an angle of 40° to 50° to S by W. — this was on the ridge of the hills. — on south side however of Berkleys sound the beds dipped to the SSE. — parallel ranges of hills are formed of this rock. & it is remarkable that they all dip to the South. so that the north side of all present basset edges. — It is difficult to conjecture, what sort of force would thus rupture the strata in parallel lines, but only elevate one side. (a) — There is however one curious exception to the dipping in one direction: it occurs within a regular range of quartz (it was where specks like mica were found), which dipped to S 1/2 W at angle 19°. It would seem as if in the line of elevation there had been a point (or rather oblong) of upheaval from which, the

30° - 40°] added pencil in margin.

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(a) Earth-quakes have been attributed to the vibration of a fluid beneath the crust of the earth. how would the crust be broken by waves on a greater scale? How does a field ice in the arctic ocean pack, when acted on by the swell from the ocean? —

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1833 March E Falkland Isd. — 111 7 (X)

strata on all sides dipped; at four nearly opposite points the following were the dips: — on north side. to N 1/2 E, 28°: on East to ENE, 14°: on South to S 1/2 W, 29°: on West to W by N 1/2 N, 16°: Vide (a) the four stations were chosen where strata were best seen. — on the top of the cone oval mound the strata were nearly horizontal & on the East side the dip was least regular. On both West & East side. a small valley (full of fragments) only separated this hill from the regular chain, where the North side had its basset edge. — the strata were much broken. & the upper ones were cracked or widely separated; especially on the West side, where you might ascend in a broad crack on the curved dome & flanked on each side by strata dipping towards opposite points: — The summit of the hill cone was about one hundred yards across & flattish: From what I have mentioned both with respect to the sandstone & quartz. it appears that the general point of dip is within some degrees of SSW. — The direction therefore is WNW & ESE: this is common to the ranges of hills & the valleys. — also the Sound & its arms run in this line. & the islands in it are equally show the same thing. — These facts strengthen the accuracy of WNW direction of stratification. —

The occurrence of vertical laminae of slate both above & below the sandstone has been noticed: at the place where I most clearly saw this fact. — the slate ran W by 1/2 N & E by 1/2 S, & the

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(a) [sketch]
N W E S
Crack: nearly horizontal fracture
N by 1/2 E, 28°
S 1/4 W, 19°
W by N 1/2 N, 16°
E N E, 14
S by 1/2 W, 29
about South
:do:
At some distance in this direction strata dip to SSE, 46°

General range of hills on South side of Berkleys Sound

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1833 March E Falkland Isd. — 112 8 (X)

(a) sandstone dipped to W by S, 14°. — the former being the usual direction for slate, as the latter is an unusual dip for the sandstone. —

At the passage from the Quartz rock to slate. the two nearest sites where I could observe dips in both; in the Quartz the beds dipped not at high angle to NNE, in the slate the laminae to S by W 65°. — Here also the slate has its usual direction, whilst the quartz (by no means pure) dipped to the quarter opposite. to the prevailing ones.

I may here notice if a horizontal ned with vertical laminae should be elevated, if the new dip was in the direction of the laminae, these latter the position of these latter could not be perceived to be altered; but in proportion as it was different so would the laminae be affected. — From the above observations under such various circumstances & sites, we may conclude, that during formation of the slate a cleavage in E & W (or E by S & W by N) was impressed on it. — that the tr upheaval of the whole mass. has but slightly affected its apparent position; we have already shown that the same cleavage was produced after successive epochs periods & changes in the nature of the deposits. — It yet remains quite inexplicable to me (Vide Geol: of Tierra del F:) that the direction of the cleavage should be same as that of the real stratification (excepting by chance); in this case however, it is nearly the same; within a point of E SE & W NW being common to both. — It may be observed

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(a) Studying this slate. was a fine lesson of caution even where the shells were present. there was not the slightest line to point out true stratification; in one place, previous to discovering the sandstone, I saw some fissures dipping to NW by N, 35°; there from being parallel & not far apart, I at the time thought might be strata. —

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1833 March E Falkland Isd. 113 9

that the direction of cleavage & form of land is almost exactly the same in this island as in the Southern part of Tierra del Fuego. Is this accidental? the distance is about 340 miles in a SW direction. & in this case the formation is transv fissiliferous. & in Tierra del I had reason to suppose it was not so; yet it is difficult to imagine it only to be a coincidence.
Patagonia Brazil Peru — Anglesea —

As I have not the slightest reason for doubting the accuracy of the facts respecting the transition of the Quartz rock into clay slate (a). it appears to me a most curious & instructive circumstance, viz. that during the deposition of such great beds of crystalline siliceous matter, various species of animals could exist; that the same fluid. which held in solution the silex, could support animal life. — If this rock is allowed to be of such a nature, as to require S its solution in some fluid to account for its origin; I can see no difficulty in Granite or similar rocks having been likewise formed when at the time same time, that animated beings existed in the menstruum. I do not believe in this very Quartz rock. the slightest trace of organic remains could be found, yet we see in a subordinate bed they are present in great numbers. —

If we vaguely conjecture concerning the first origin of this whole formation, we may imagine a sea in which the Quartz was gradually depositing, & that into this a current

Patagonia Brazil Peru — Anglesea —] added pencil.

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(a) It is unquestionable that the slate formation lies between two great ranges of slate quartz rock. —

It is also interesting to find, with the Quartz, deposited from water, in which animals lived, specks of Mica.

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1833 March E Falkland Island 114 10

brought either fine sand or mud. — On such a ground animals flourished & by successive additions were finally intombed & their casts preserved in their present state. Where the current only brought small quantities of extraneous matter it united with the siliceous & formed these rocks which partake of the characters of both. In support of this. as far as my limited observations go, it is only in the neighbourhead of the slate that the Quartz ranges of Quartz hill. contained the fine aluminous powders. —

The country is very generally covered by a ned of peat; this in some places is about 12 feet thick, & most frequently rests on a white clay bed. — When this latter was formed it is not easy to conjecture. — From the changes which are always going on, there are low cliffs. composed of the clay. then peat & covered by dunes of sand, all at present being destroyed by the sea. — The peat bears the signs of great age: in one places the lower part is of remarkable compactness & great specific gravity. 1132 — At present I see few signs of the increase of the Peat. (a) — there is but very little, in detached spots, of the Tierra del Bog plant & no great pools with moss. —the poor wiry grass adds a little to the mass. but it never could have formed such thick beds. — Circumstances at some former period must have been more favourable to the growth of peat-forming plants. — (b)

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(a) This specimen was taken from the bottom of a bed about 12 feet thick; it does not burn so well as the more fibrous & less compact soils. —

(b) 1834 March

My opinion is altered. I believe the Peat to be formed very slowly, from the grass & other plants. now growing on the surface. — I think so from seeing bones &c &c lying on the grass. becoming partially enveloped; & from observing how extraordinarily favourable the climate is to the production of this substance. — Even at the sides of the stream of fragments where there must be such perfect drainage, peat is beginning to grow. — V. Append. P. 15 — likewise in the very centre, where two or three blocks lie pretty close an island will commence to form

A whole chapter beginning of II Volume about the streams of stones in Pernetty voyage1

Mem. black clay slate. near Quartz.

1 Pernety 1770.

Mem. black clay slate. near Quartz.] added pencil.


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