RECORD: Darwin, C. R. Geological diary: St Josephs Bay. (1833) CUL-DAR33.223-226 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. 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.


223

1833. St. Josephs Bay (43)

This was is the most northern point, where I have had an opportunity (& this only for half an hour) of examining the great formation characterized by large oysters. How far to the North it extends, I know not, but certainly for 30 or 40 miles. to the South we shall meet it, with some interruptions of old crystalline rocks nearly to the most southern part of Patagonia. —

(Stokes)

The cliffs, on the East side of the harbor, are about 70 100 feet high & irregular. — The lower bed nearly 1/3 of whole is composed of yellowish earthy sandy clay; & earthy sandstone which is also slightly calcareous. — I should think at least 1/5 of its mass consisted in shells. — They are confusedly placed in the body of the bed. —

1356 ... 1365 The shells are chiefly the great oysters, which are perforated by a Cliona (Grant) & Pholas (?) & marked by dendritic manganese. (a) — there are very many Pectins, some Turritella & Balani &c &c; some parts were almost composed of small Corallines, which appear to me to be the same with some which I found in 30 fathom water on the East coast. of Tierra del Fugeo. viz. Flustra Relipora, — cellaporaria & a Caryophyllia. — These shells did not blacken or emit any bad odour under the blow-pipe.

Above this conchiferous bed, was another, whiter, more aluminous, much finer grained, 1367 which containing contained no calcareous carbonate, or organic remains. 1368?? — but very many layers of Selenite. These were an inch or two thick generally horizontal, sometimes tortuous. — Above this we have a bed, a few feet thick of the Porphyry pebbles, noticed at the R. Negro. — they consist of dark colored porphyries, with small crystals of feldspar. quartz & some mica & some siliceous ones pebbles. G

nearly] added pencil.

(Stokes)] added pencil in margin.

yellowish] added pencil.

& earthy sandstone] added pencil.

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223 verso

(a) A Spaniard (in writing informs me) that on the surface of the layers of oysters, one may see a complete collection of every plant in the Peninsula painted with admirable delicacy!!! — From the same mans account the grand Salina must be in a considerable depression.

224

1833. St. Josephs Bay (44)

They are small & exactly resemble those which will be described at Port Desire. The gravel at the R. Negro, was cemented by calcareous matter & contained crystalline nodules of gypsum; we have nothing of that sort here; the gravel shows more signs of violence, it follows & fills up inequalities in the lower beds. —

G

I could see the black line of the gravel running for many miles up the coast. —

Above the gravel there is a bed, several feet thick of sandy earth, which contained numerous patellae & Mytili 1366, a few Bucanus & Balani. — The Mytili & Balani partly retained their proper colors of blue & pink. (b) — All the shells emitted, when burnt an animal odor. —

These shells are the same, with those, which at Port Desire are proved (a) both now exist on the coast & to be lying on the elevated plain. — It is very interesting to read this account & then that of P. Desire & St. Julian, places 470 miles distant, with formations so exactly similar. — The modern superior shells prove, in both cases, that the beds have been upheaved at the same period & that a very recent one. —

I have been informed., that at the head of the Bay (where the cliffs are higher) there is a petrified whale bones & likewise many crabs. —

Also in this district there are many large Salinas. — In the extensive W by N & E by S section, seen North of the bay; the lines of stratification are seen to be most perfectly

G] added pencil in margin.

224 verso

(a) I did not notice any of these modern shells, on the Porphyry gravel at the R. Negro. — But the Mr Stokes says that at P. St. Antonio, the country generally is covered with many which very probably are such as above.

(b) On one of the muscles there is the encrusting Corallina. inarticulata. with its generative paps, described at the Falkland Islands. —

225

1833. St. Josephs Bay (45)

parallel; but it is evident they all dip at very small angle to the Eastward. — It could only be perceived by following a line, which several miles to the west, would be some feet above the water line, from which it would gradually lower itself, till it dipped beneath the water. —

I, at that time could not credit, that whole tracts of country could be elevated with so little violence & I attributed the present relation of the land & sea, to a subsidence in the latter. — I imagined this Easterly dip. was caused by the same circumstance, which at the present day unquestionably was forming beds. beneath the ocean with the same dip (viz the gradual slope of the bottom). Now this whilst I believe in the upheaval, it appears to me that this is quite a more probable an explanation of the dip than a tilt during the elevation. —

Age of Bed. The occurrence of the great oysters at St Fe Bajada has been described. — I believe some other shells are the same. — No great similarity can be expected, as there is a difference of no less than eleven degrees in the latitude of the two places. — The mineralogical character of the beds is somewhat similar. — Salenite &c.

I have little doubt that two beds. belong to the same formation, that is formed under the same geological period, or nearly the same time. when some I have given some slight reasons for supposing that the Tosca formation in which is included the Limestone & Oysters of the Bajada & A. de tres Vivoras, is contemporaneous with the the R. Negro sandstone.

226

1833. St. Josephs Bay (46)

If the Patagonian & Bajada beds could be proved to be of one formation, then the above reasons, would apply to show that the great Patagonean oyster formation & the R. Negro sandstone were contemporaneous. —

And this I believe to be the case. — I think the one fossil (an Anomia 1540) found at R. Negro (& my memory of a bivalve) is common to the oyster; but we have in the two layers of gypsum. (b) —

But whether contemporaneous in their depositions, we are certain, they were at the same time at the bottom of an ocean, & being then together covered by Porphyry pebbles were elevated into level plains. — I imagine the differences only to be caused by local circumstances. (entrance of river &c &c) which might well happen in a distance of more than 60 miles. —

All the above conjectures would go to show, that the Patagonian & R. Negro beds are contemporaneous & likewise that of the Tosca (with the oyster beds) or rather that the superior ones in this latter formation were deposited at the same time the gravel was spread over the R. Negro sandstone; which gravel, when it has extended, seems to to have destroyed the inhabitants of the then existing sea & that subsequently a new race appeared. — So that perhaps. the oysters of the Bajada &c may be of rather a more modern date, than those in Patagonia. —

But these oysters, although in the northern part not destroyed by the gravel inundation (a), have in all

226 verso

(a) probability long perished from the world. —

(b) The layers or beds of calcareous matter in the sandstone, would in the Patagonian formation go to create compose the immense shells of the ostrece-pectins &c &c. —

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