RECORD: Darwin, C. R. 'Reflection on reading my Geological notes'. [3.1834] CUL-DAR42.93-96 Transcribed by Kees Rookmaaker (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrections by John van Wyhe 10.2011. RN1

NOTE: This document is continued in CUL-DAR42.148. See the excellent fully annotated transcription and discussion by Sandra Herbert in Herbert 1995.

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Reproduced with the permission of the Syndics of Cambridge University Library and William Huxley Darwin.


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: Reflection on reading my Geological notes :

V. Caldcleugh. Geological Map.

We have seen The Tosca formation commences near the R. Colorado from conversations with individuals. I think it extends It is said to extends to some many many miles north of Assumption in Paraguay. which gives ,about (a) 1100 miles in a N. & S. line. — I should not be surprised if it extended much further northward; keeping a mean distance from the Cordilleras, & being bounded to the East by the mountains of Brazil. —

Miers Chili states that near S. Luis there is a ridge. with gypsum & I see in chart "los Gigantes". To the Westward there appears to be the Traversia. — The Banda oriental. Tosca. I think certainly is of same age with the great plains. — Assuming this We have then the greatest breadth of about 700 miles. This great immense formation is probably bounded on the S.S.W. WNW by the sandstone plains or Traversia. — (to the N. we know not its limit) to the NE. by the Mountains of Brazil.

(Perhaps a line from the laguna de los Patos. in a NW line may mark the separation). to the E & SE. — the ocean. = The sea in which this was formed would probably be partly we be a little sheltered by the ridge of the Andes.. & the mountains of Brazil: the its origin doubtless arises from the Volcanic agency of the Cordilleras. — its saline ingredient, its gypsum its calcareous nodules: the uniformity of the red earthy clay (or Tosca) is problematical I imagine from Miers Chili. there are such beds in the very mountains. — These are several points very curious with respect to these beds. — The very general

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a. The actual limits in N & S line of Megatherium relics is 550 in E & W. — 300.

Azara

Vol I Azara p 55 All countries east of Parana non-saliferous Salinas in Chaco on coast of Vermejo p. 56

Bright coloured clays abundant towards confines of Brazil —

Starting

The Bajado bed would look like marine deposits: eventually covered by the old Plata. Alluvium or rather the site where marine & alluvial deposits alternated. —

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absence of shells. — we see them in an included bed included in the Tosca. from the Tosca Colonies to Bajada in a NW. line (perhaps which turns more Westward to Cordova):

This from the pebbles particles of quartz. in the Limestone & pebbles of granite. in the red sandstone we may imagine to have been nearer to the old coast of Brazil mountains. — (The greater abundance of Lime here in pure form. may perhaps arise from springs percolating the granitic rocks. which to the North of Maldonado we see contain so much marble?—)

Another point. is the vast numbers of fossil bones of very large quadrupeds. — Their age with respect to the shells I cannot make up my mind: That the view. which I took. respecting the relation of these shells. with the Patagonians one is correct viz. that they existed a short time subsequently to the more Southern ones being destroyed by the Porphyry pebbles; but that now the greater numbers of these species do not exist; perhaps destroyed themselves perishing during the elevation deposition of the superior Tosca. Those sp It is certain that during & before the existence of these shells Tosca in its truest features. precisely resembling was deposited (∴ surrounding circumstances similar) but that the Tosca which contains in some many instances fossil bones was posterior to the shells. — I have already stated. that the Tosca (for instance) of the Salado) which contains bones is more closely allied to that inferior to the shells. but its real relation I cannot say. —

I think we may be certain. that during before the deposition of the superior Tosca (with bones), the bottom of the

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Compare the great extent of same mineralogical beds of Patagonia — with secondary of Europe: Here mineralogical evidence tells in this quarter of the globe (perhaps across the Andes) quite useless when compared to Europe. —

Would depression of Continent by covering up Salina bear comparison with the Salt of Europe.?

The passage of the Tosca to fossiliferous beds, by Tosca rock at Bajada important. —

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sea. had undergone some elevations. I think this from the great denudation of the ferruginous sandstone in B. Oriental. —

There arises a question Whether these animals existed after the final elevation of the Tosca plains, must remain doubtful; of the fossil remains certainly a small proportion, if any belong to alluvial formations subsequent to the superior Tosca. There arises a question. what country supported these numerous & vast animals: in the country. bordering on Brazil (or B. Oriental) it is obvious: but it is more difficult to answer. when we find skeletons, with their bones in groups in such situations as at the R. Salado. — Where the whole country for 100s of miles belongs to the same formation & near to where for same distance there is no higher land. — I can only account for it on the principle of putrid carcases floating. as mentioned in the grand Seco. — How vastly numerous must these animals have been for their bones to cover such an area

At. B. Blanca. I suppose the animal (of which I found skeleton nearly entire) must have lived previous near about to that late & trifling elevation modern beds: It as well as the Cavies M. Hermoso might have lived & Megatheriums remains might have lived in the Tosca. rock plains. which I have supposed to be elevated before the deposition of these beds. — But then we have the puzzle how could these most sterile plains support such large animals: The very same puzzle & explanation of occurrence, refers to the bones at Port St. Julian

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In the central Pampas. perfect uniformity in nature of bed (which is not the case at B. Blanca) & very little, but regular height above the sea. — cannot admit of many separate elevations, for upon the former of which animals resided.—

I may add with respect to absence of shells. as a conjecture, that where gypsum is dissolved in water shells do not flourish. at Port Desire, St. Julian & St Jose above highly conchiferous strata. there was Gypsum but no shells. (excepting one vestige of a Univalve). (The Bajada. appears an exception. but I am not sure in which bed the Gypsum occurred.

from what I chiefly saw (& was told) was at bottom of the cliff. — V English Geology. & Paris

With respect to the R. Negro. my views, I think are correct. I believe it essentially to be the same with the Patagonian Oyster bed. — Sand in this case (as it seems in so many formations) preventing the cha calcareous deposits being converted into organized shells. — The shells on the surface at Port St. Antonio. where in all probability the Sandstone extends. proves what I think. there can be no doubt. of that the sandstone was beneath the ocean & arose from it at same period with the Patagonian beds. —

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The great oyster bed extends from 20 (or more) miles North of St. Joseph to [blank] in distance [blank] miles. — Some difference in the organic remains must be expected where we have so many degrees of Latitude. — The leading features are the same. the Ostreæ. & Pectens. & the Turitellae at Lax Bay & St. Julian. — It is remarkable to see the great similarity of the beds at the extreme points; the conchiferous bed. covered by the aluminous beds. with gypsum. are universal & then again by Gravel. — We must attribute this to some change taking place in the Cordilleras some period of activity commencing: these superior beds. although evidently not favourable to life. yet permitted some few alternations of the shells. as seen at P. St. Julian. — But the great change. was effected at the pouring forth of the Porphyry pebbles. — I have never seen the Parent rock: the stream from the Southern parts. must (I think) have come from the NW. because. the Andes in these Parallels I believe to resemble Tierra del Fuego. — That they came in a body short period I think probable from their not being encrusted by stony small corallines. — (Which I always have noticed to be the case in these seas) They must have been already rounded at their source. — Were they lying in masses on the West foot beach of the Cordilleras & during

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(Z) From the little I know about recent shells. I have not grounds enough to go on; but I have found one shell alive in Tierra del Fuego which is found in these beds perhaps some of the Pectens. — Again I do not believe the great Oysters are now alive; [illeg] so remarkable a shell could not escape observation.

Gravel

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an early & vigorous elevation. carried by the retreating waters to a deeper sea? — Whatever their origin. they mark a great change in the inhabitants of the ocean: during a succession of elevations, such shells as now exist — flourished on the successive lines of beach & were scattered over the bottom. —

This gravel bed. (x) shows signs of force. filling up inequalities probably of its own making. its extent is very great from N. of the Colorado to a distance of miles: On the coast of Tierra del Fuego. (C Ines) there were many such Porphyry pebbles & even some small ones off Staten Land. which I believe to owe their origin to this bed. — though perhaps washed by currents to these distant points. —

Looking at this whole part of Eastern side of S America. we must considers it as one grand formation. — In the Northern parts it seems to repose on the Crystalline rocks, some of which in their lines of cleavages & elevation. & mineralogical nature are allied to the Transition formations of Falkland Isd. & Tierra del Fuego. — at. Port. Desire & Northern Parts of St. Georges Bay Gulf. there is much Porphyry. which from its mineralogical nature & included Conglomerates. I imagine to be secondary. —

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(X:) This gravel in its Northern limits seems to mingle with another set of phenomena. — the formation of the great Tosca rock formations; it. &c

fills follows the inequalities in Salinas in R. Negro Sandstone

(M). Secondary (?). the Quartz at C. Blano & N. of St. George. is most probably closely allied to Porphyries if so all Transition: N.B. Conglomerates at C. Remarkable in T. del. F

It may be doubted whether Porphyry of P Desire has any immediate connexion with the Andes.? V. those of Maldonado & still more of P. Alegre

V. Caldcleugh. for limits of Tosca

Volcanic rocks (concealed) in M. Video. R. Negro

Mem. supposed do. R. Grande Mr Fox

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But with this exception the hiatus (as compared to Europe) between the Crystalline & Tertiary beds: (Videlicit. B Oriental) is very remarkable. — We shall presently mention the sa run over the proofs of repeated elevations:

May we conjecture that these have long been going over, that for some. began with greater (x) strides, that rocks from seas too deep for life (. or if any were rapidly elevated & that immediately when within a proper depth. life commenced.

(Port Desire rocks before this period). & its signs are now present in the great oysters &c &c The elevations rapidly continued; land was produced. on which great quadrupeds lived: the former inhabitants of the sea perished (perhaps an effect of this these changes) & were scattered on the surface on the new beaches the present ones appeared. — The present quadrupeds roamed about the increased surfaceon the new plains; fresh elevations destroyed, the continuity of this plain & elevated (V. Tierra del Fuego. I anticipate for the sake of connexion) beds containing leaves of the present trees & inhabitants of the present deep: And such beds are doubtless now forming beneath the ocean. ready when comm compelled to give their evidence in the open day-light. —

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(x) Perhaps the first opening of the N & S. crack in the crust of the globe. forming the Cordilleras

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The study of this Geology is very instructive from the consideration of the greatness in extent. & perfect (z) horizontally, of the & number of the Elevations:

We have nothing here like anticlinal tilting on each side the strata into highly inclined position: it rather a swelling of the Globe, on the largest & most regular manner. for an extent of latitude equal perhaps to 2000 miles. or even more. (& certainly from to the extent of 1000 miles but is narrow in proportion &. & that in this latter (& without doubt for all) within a period in which a. 2 species Muscles & a Balanus has retained. exposed to the atmosphere its their proper colors: — The Andes have been supposed to be a longitudinal crack. would not this probably occur during an elevation of such an a longitudinal enlargement.—

But after this crack was opened. the matter which came out. from the newly formed mountains was formed into beds &again & again. elevated:

It becomes a problem. how much the Andes owes its height. to Volcanic matter pouring out?. — how much to horizontal strata tilted up.? how much to these horizontal elevations of the surface of continents? — Another problem is how long will shells exposed. as I have stated will retained retain their color? — (V other side of Page)

V. According to this crack from stretching. the beds ought not to be tilted up excepting on the edges. when near the flowing matter which would be produced by explosion of central metal & oxygen

: If otherwise plains would increase rapidly in height as approaching the Cordilleras:

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(Z). There is one fact which appears to me preeminently curious the entire absence of all Quartz pebbles. on the Tosca rock plains surrounding lofty, but broken ridges of the Ventana. — It proves the extreme quietness with which these plains have been elevated. & shortly after their hardening. — Any few shells or gravel would be washed away with retreating water

The degree of force (& perhaps number) of elevations has differed in different parts of the coast. the. sea-like low Pampas. — & the plains pieces of table land of different altitudes in St Georges Gulf. some reaching to 1500. feet.

at St Julian to 900.. yet all to the eye most truly horizontal. —

It may be remarked. that the increased elevation above the sea in these Southern Plains may partly be explained being near seat of violence (??) & not. at Mendoza & San Luis plains are said to be 3000. ft Miers Chili.

When the Sierra Ventana plain was elevated any small pebbles &c lying on the surface would be carried away by the retreating waters

Dessalines. D'Orbigny has given account of Pampas: Where?

Caldcleugh. has geological map of Pampas in Travels. —

M. Bonpland. do —


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