RECORD: Darwin, C. R. Geological diary: Pampas. (1833) CUL-DAR33.249-278 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Kees Rookmaaker, checked against the manuscript and edited by John van Wyhe, corrections by Gordon Chancellor 6-11.2010. RN5

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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.


249

1833 (1) The Pampas

In the months of August to November, I made three excursions in the Pampas North & South of B: Ayres, from Latitude 31.47 to 41. South. I will begin with the most northern point St Fe. & so proceed: but there will be many inversions of time, from having seen the country & written my notes in a different order.

The country as far South as the R. Colorado is mainly characterized by one formation; the substance of which this is composed, is called by the Creoles "Tosca". — This has been mentioned in my notes at B. Blanca & B: Ayres. — Tosca is a tough earthy clay, of a more or less red colour; it contains, beds, layers of nodules, stalactiform masses & small rough concretions of an argillaceous-calcareo rock (a); which I shall call Tosca rock. It is hard, often coloured pink & marked with dendritic manganese, as the proportion of lime varies much & with it the degree of whiteness: in the same bed & situation the quantity of Tosca rock in the tosca. varies, from scarcely any till it forms the sole substance, in which case however it is generally cavernous. — The more calcareous sorts. form the most entire beds. —

Soundings off much of Plate side extent of mica

(b) At St. Fe. Bajada. on the East coast of the R. Parana there are perpendicular Cliffs estimated from 60 to about 70 to 80 feet high. — The lowermost bed is a black bituminous clay 1577; in many cases the vegetable fibres are evident. — it is deposited in curved, highly inclined plates, such as rapid streams form & even may be seen in the modern islands in the Parana. — Above this comes a thicker bed of yellowish sandy clay; this

249 verso

(a) In parts, where the Tosca rock is abundant, this alone is called so by the Creoles; but where this more earth substance it is prevalent, the name is given as I mention. — This name probably originates in 'tierra tosca" "or coarse earth."

(b) Is more generally now called the city of Parana; it is the capital of the province of Entre Rios. —

De la Beche. Translation of Annales des Mines p. 15 account of small tubular cavities in F.W. Limestone of Paris1

To West of Sierra Ventana water drains into chain of lake. effect of elevation
mud nucleus of Ventana

1 De la Beche 1824.

250

1833. (2) The Pampas

contains an abundance of shells 1570-1572, scattered in its mass 1599. — There are some oysters, Pectins, Arcae &c &c. (a) — Above this is a Limestone bed, which is however often separated from it, by a bed feet thick of greenish fine grained clay; of with a remarkably unctious feel. — it decomposes & shrinks into small angular pieces, when exposed to the atmosphere; from this cause, it soon wears away, & thus occasions large masses of the Limestone to fall & be ready for the Lime kiln. — This latter bed, which hardly deserves the name of Limestone is in its purest form 1564. 1565, white cellular & crystalline or compact 1566. — from this it takes assumes every degree of impurity, untill in many places it is an earthy sandstone. — When most earthy it contains very many large Ostreae. 1568. 1569 — In the hard rock there are impressions of shells 1567, teeth of fish 1510, (& it is said large bones), cols & a few pebbles of coloured quartz. — It is not in many places that the Limestone is pure enough to be worked. — Above In upper bed of the Limestone there are layers of very fine white sand. — Half the height of the cliff is formed with the above rocks, the superior part is Tosca, which will presently be described. —

At Punta Gorda, about 20 miles to the South, there is this same limestone, which I observed to be nearer the water. — At the R. Hernandarias, it is said, the cliffs contain shells, & from what information I obtained, there is little Doubt this formation extends (b) at least 20 or 30 leagues up the river. To the West it can be traced (by ravines) across Entre Rios (1.35 miles) to the Uruguay (c) where it passes

250 verso

(a) In the sandy clay, there is much crystallized gypsum. — (point of resemblance with formation of South Patagonia)

(b) Mr Bonpland has examined all this country & sent a series of specimens & description to Paris. —

(c) The Caleras of Barquin & several others name the Arrayo de la China & Paysandia. —

251

1833 (3) The Pampas

cliffs & is burnt. — In a direct SE line, I hear of it at Matanza, at head of R. Namkay. At the mouth of A. de las Vivores in Banda Oriental I examined it (a distance of 180 miles) & in other places in that Province as will be described. —

At Cordova, I have been told by an intelligent man, that there is Gypsum & shells in the banks. — likewise marble. I suppose this latter occurs in the North & South [Cordobera] range of Hills. — (Miers Chili). —1

I have omitted to mention, that in the Estancia del A. de las Conchilas, near the Bajada, there is a ferruginous sandstone, in which is found much petrified wood — the man owner who gave me the specimens (1573 ... 1575) 1573 ... 1575 communicated this information. I have no doubt this bed belongs to the oyster formation; it is interesting, in as much as it explains the frequency of large blocks 831 ... 834 of silicified wood being found in the coast of the Parana & Uruguay. — The belief that these rivers now have the power of converting any substance into stone is most firm & universal in the country. — There are many curious stories current, such as Artigas2 being in want of gun flints, had a proper number if pieces of wood cut into the proper shape, which after a short submersion, became excellent flints. — There is no part of the human body, which they have not seen in stone: but as I have seen a coloured flint which they I have been assured was originally Bacon & another which was a peach-stone (1544) 1544 I shall disbelieve all these stories, which doubtless take their rise (a) in the existence of the silicified wood.

1 Miers 1826. vol. 1 Text, vol. 2 Text

2 José Gervasio Artigas Arnal (1764-1850) a leader of Uruguayan independence.

251 verso

(a) An intelligent man informed me that the bones of horses & oxen are frequently petrified in the A. de la Conchas; & that M. Bonpland had examined them. This appears strong evidence. —

Big bones

Big bones] in pencil.

252

1833 (4) The Pampas

We will now return to the Tosca above the Limestone, it forms a bed between about 40 & 50 feet thick; the upper half being bright red. as the lower is pale:

A little above the Limestone there is a bed of Arg: Caleario. (1561) (or Tosca) rock, marked with dentrition manganese; its surface is has a concretionary appearance:

We can easily imagine this to be formed in the Tosca, by the same cause which produced the Limestone adding a little Lime. — In the upper part of the cliff there are some few small round concretions of Tosca rock (b), & an irregular layer of yellowish indurated sand. (or soft sandstone) such as I have noticed at B. Ayres. — At the A. Tapas, which enters the Conchitas, 2 miles from the town, I visited some broken cliffs, where a few years previously bones & part of the (Megatherium) case1 had been found. — The Tosca is of a red color, & contains numerous small concretions of Tosca rock 1562, some whiter or more calcareous than others; it is unquestionably above the Limestone. (a) — Part of the Armadillo like case remained; when the Tosca was removed, it formed a sem well or hollow between 4 & 5 feet across & the internal surface quite smooth.

All the bones had been removed.. — In every part however of the cliffs, on the borders of the streamlets, there are very numerous fragments of bones 1582 1583 1584; They were however so very soft & decomposed I could scarcely extract even so small a fragment. I saw, what might rather be called the figure, than the reality of a large tooth, such as I shall subsequently mention finding with a large skeleton on the Paranas.

In an highly inclined (60° 60° to 70° ?) surface of compact

8

1 Darwin refers to the bony case of the Glyptodon.

252 verso

(a) In the province of Entre Rios, I heard of large (or giants bones) being found a little SE of Punta Gorda, & at. Malanza, at the Arroyo del Animal. — This is a stream to the East of Noboya & West of R. Gualeguay. — The skeleton from which it takes its names, appears to have been tolerably perfect, it was found at a considerable depth beneath the surface 7 was discovered by the Arroyo forming for itself during a flood a partially new course. —

(b) This bed of Tosca rock is important because it shows a gradual change from the strata with marine shells to the Tosca or red clay with concretions of Tosca rock. —

Bones

Bones] in pencil.

253

1833 (5) The Pampas

red Tosca I found a horses tooth (1581) 1581 firmly imbedded & excepting one, point hidden from sight. —1

Its being a Horses tooth, would alone have was the only reason which made me doubt its being contemporaneous with the other bones. — We must suppose the Tosca had been long since (for the tooth is slightly stained) washed down & rehardened. — Upon, however, the most careful examination I could not perceive any certain signs of this removal. — Have not horses bones in N. [America] been found on in very ambiguous situation? Jamesons Edinburg Phil: Journal. (a) — If the tooth had been in a vertical cliff, there could have been no doubt. —

I may here mention, that it is said, there are Salitrales in Entre Rios. — there are muddy places, which in summer have a white saline crustation supposed to the be saltpetre; I shall have occasion often to allude to them again. Azara wrong —

Proceeding to the South, we see by inspection of a map. that from P. Gorda to the Uruguay to East coast of the Parana is a low alluvial plain; it is intersected by arms of the river, formed of sand & mud & covered with bushes. Of a similar nature are the islands in the Parana. — V. Journal P. 388.2 — On the East shore from St. Fe to near the A. del Monge, the country is very low & covered with spiny low trees of Mimosa (?). — This is inhabited by Indians & little known.

From this point to B. Ayres (& far South of it, as will be described) the country both in external appearance & geological nature is singularly alike. — (V Journal for some short descriptions).

The Pampas (of St Fe more especially) are most

1 The tooth was described by Owen in Fossil mammalia, pp. 108-9. See also Journal of researches, pp. 149ff.

2 Beagle diary, pp. 195-6.

253 verso

(a) For some trifling reasons, why a horse was not an original inhabitant. V. Journal P. 363. —1

(b) It is curious, that in these islands nearly about 300 miles above where it joins the sea, is the Plata. There is not a single pebble, not even a fragment larger than a grain of sand; yet there are floods which raise the river from 3 to 5 yards above its ordinary level. —

(a) I must re-urge that I have if anything overstated an the cause of doubt respecting the position of the Horses doubt tooth. — Equally I might doubt respecting nearly all the fossils; for few were in absolutely vertical cliffs: — Now that I find (appendix to Beechey. P 348)2 that horses bones have been found with the fossil Elephant. in my own mind I am convinced that a horse coexisted with the Megatherium & Mastodon: How strange that man after an immense epoch should repeople the country with the same genus. — I believe all Historians are agreed that the Spaniards found no Horse in S. America. —

1 Beagle diary, pp. 181ff.

2 Beechey 1831.

254

1833 1834 (6) The Pampas

remarkably level. — Judging from the perpendicular cliffs, seen on the West shore of the Parana I should think they were elevated between 40 & 60 feet above the level of its waters. As I sailed down the river, & observed (as far as my eye could judge. that for leagues together, there was not any change in elevation. I invariably came to the conclusion that the sea, in which these beds had been formed, had subsided & not that land the bottom had been elevated. — There has been but little alluvial action in these plains: the valleys are all explicable, & in proportion to the present streams which enter the Parana. — I must except one depression between the towns of Luxan & Areco, a corresponding & large break in the cliffs ( is seen on the Parana. near where the little streams of La Cruz now enters.

Some of these small Arroyos or streams are brackish in the summer. In the beginning (1st) of Peleton the Saladillo, near Rozario, was very salt. — the Carcarana & Monge were a little so. — In Encyclop: Britt. — salt is said to be found between St Fe & Cordova. — And on authority of Azara, that Sulp: of Magnesia at Melinari. — (a small town in Lati: of St Nicholas & about 70 miles in interior).

Beginning at the North, the first section of these plains, which I visited, was on the banks of the R. Carcarana or Quinto. This place has long been celebrated for its large fossil bones. The old Jesuit Falkner mentions them, together with the Armadillo-like or Megatherium case. I heard of very many

254 verso [blank]

255

1833 (7) The Pampas

which had been removed & placed as gate posts & thus perished. — The lower part was a pale Tosca, with many stalactiform masses of Tosca rock: in this I found a remnant (so perfectly decomposed I could not extract any portion) of a large grinding tooth, apparently the same as those found on coast of the Parana. look to notes — Above the Tosca, there was a layer of small white Tosca-rock concretions, marked with Manganese. from amongst these I extracted, what I imagine to be a large cutting tooth (?). (1406) 1406. Above this layer there was a bed of very soft impure sandstone. — This section near St. Miguel:

A few miles from this, is the same Estancia of Gorodona, on the coast of the an arm of the Parana. I t heard of some giants bones. — They were in the perpendicular face of the cliff & was obliged to approach them in a canoe. — There were two large deposits of these bones, that is two skeletons the bones of which were rather scattered about. — They were about 6 feet above the level of the river & in the floods must be covered; from this cause they were so entirely decomposed, that I was unable even to remove one of the grinding teeth (a) entire. — I have some fragments. (1409) 1409 & a bit of one of the ribs (1585. 1586) 1585. 1586. — The Tosca in the lower part, where the bones were, contained very numerous nodules & stalactiform masses of Tosca rock. — the upper part much less. —

Beneath. this there is a bed. (close to the river) of pale yellowish clay, abounding with curious

bones] encircled in pencil.

255 verso

(a) I believe it to be the narrow toothed Mastodon: a tooth, which I saw at B. Ayres & which came from the R. Arrecife precisely resembled those drawn in Griffith Animal Kingdom.1 — Consisting of 6 main points, with the summits worn off; the many of the joints consist of an aggregation of cones or points. — I have seen several such teeth in possession of different people. bones — one was from the R. Salado (where Mr Parish's Megatherium came from). — If it is the tooth of the Mastodon, this animal is contemporaneous with the Megatherium, for there is no doubt that the Armadillo-like case has been found in the same bed. Both from Falkner's & other authorities. —

This is rather an interesting fact. —

x. It is odd having seen 4 or 5 6 or 7 teeth of the Mastodon & never one of the Megatherium, (that is if from description I know the tooth of the latter). —

1 Cuvier 1830.

256

1833 (8) The Pampas

hard ferruginous cylinders (1563) 1563. (a) In descending the Parana I could trace by change of color, this bed to near Rozario. — We may perhaps suppose it is analogous to the yellowish earthy clay at the Bajada. — Although these bones & those at the Carcarana, were so entirely rotten, I heard from a neighbouring resident, that he had seen some quite hard & perfect. —

bones. I was informed large bones have had been found at the Colegio de San Carlos

At Rozario the Tosca is reddish with some Tosca rock, at the Arroyos Saladillo & Seco the latter is abundant. — At the Pabon there is a small waterfall about 20 feet. over a mass of cavernous Tosca rock. it is either rather earthy (1559) 1559 or crystalline as (1560) 1560. (b) — This spot interested me as I could not fail to observe the exact identity of this bed with one far to the South at the R. Tapalguen. & as I subsequently found out with that of the A de las Vivoras at in B. Oriental: — At the A. Medio, there is much bright red Tosca. with but very little Tosca rock. — At St. Nicholas horizontal lines of variation both in tint & compactness may be observed in the Tosca? there is some Tosca rock.

From this place to B. Ayres. I scarcely found a good section. — the cliffs however may be traced from those mentioned to that on which the city is built. At the rivers of Areco & Luxan there was pale & red Tosca rock with white small concretions of Tosca rock. Bones — At the Salto, a village near head of Arrecife, large bones

bones] written and encircled in pencil.

256 verso

(a) My opportunities of seeing this part of the country was riding from B. Ayres to St Fe & returning by the Parana to the same place. — I rode from the R. Negro (in Patagonia) to B. Ayres; from this to St. Fe. — returned by the Parana: There from M: Video to the Uruguay, from thence to M: Video, where the Beagle started for Port Desire. —

(b) The Tosca rock here was perforated by minute linear serpentine cavities, often lined with black. —

Does not this occur in the water formation in the Paris Basin. — Is it formed / some Worm during deposition or sorts of plants ??

Subsidence wd account bed for extension of Tosca- formation on Pampaean mud

Subsidence...mud] in pencil.

257

1833 (9) The Pampas

B. Ayres

have been found. — At Arcas it is said small bones are turned into large ones or giants bones. — At Luxan the Madrid specimen of the Megatherium is well known to have been found. — For the geology of B: Ayres V. 61. —

bones

We thus see that these plains are composed of a bed of Tosca with an exceedingly varying proportion of Tosca rock; that they contain great numbers of the bones of extinct land animals. — I, at this time, thought that there must have been great differences in circumstances or period under which the above & oyster had been formed; & that the latter invariably was inferior to the former Tosca. —

This opinion has subsequently been altered. —

Banda Oriental

I will now pass on to the description of Banda Oriental & then return to the Tosca, which extends far to the South of B. Ayres. —

In notes about Maldonado (P 123) I notice an alluvial covering, which is of a pale reddish color & contains small white calcareous & ferrugino-aranaceous concretions & in one instance overlies white sand. — At M. Video there is seen the same bed & I have described P. 67, an agglutinated sand traversed by white calcareous plates & stalactiform masses, of the same substance. — In the barrancas de St Gregorio, to the East West of the mouth of the St. Lucia, there are cliffs from 50 to 60 feet high. — lower half of this is composed of coarse particles of quartz & feldspar without mica (a), precisely such as forms the present crust here & at Maldonado; in one place there was a narrow central clay bed; above this sand, there is a Tosca bed, in some places bright red, in others paler; it contains calcareous honey-comb shaped plates & numerous impure Tosca rock concretions 1549

Bones] in pencil.

257 verso

(a) These vary from dust to goose swan shot. —

(d) On the East coast it is said the country wears the same appearance, till about Lat 31°. - 30° on west side of the Laguna de los Patas, here the granite hills of Port Alepe first begins to shown in altitude & with them the forests of Brazil. — I have conjectured the absence of wood in Banda Oriental as well as in the Pampas. (V Gen Observ. Maldonado) to originate from the modernness of the Tosca covering. — (This will be abundantly shown)

The trees of Brazil would require greater heat, those of Tierra del Fuego more moisture & irregularity of soil. — & no creation has taken place. —1

1 This line apparently refers to the creation or origin of new species.

258

1833 (10) The Pampas

B. Oriental

these are of a stalactiform shape: & occur together in parts where both above & beneath there are very few. — in short they resemble the great Tosca bed of B. Ayres — only not quite so well characterized.

the main difference is the Tosca containing some few fragments of quartz. — The Tosca follows & fills up irregularities in the sand. — In the neighbourhead of Colonia del Sacramiento, the gneiss is covered by reddish Tosca with very numerous concretions of Tosca rock & calcareous plates, resembling that at the Bajada. — in the harbor, there are cliffs precisely resembling those of Gregoria (distance 60 miles); there was some white sand. — pale Tosca. — reddish Tosca (a). with numerous white calcareous concretions.

The separation between Tosca & coarse sand is well defined. — There is some pale earthy Tosca rock, high up the Arroyo de St Juan. —

I have no doubt all this Tosca is part of the same formation with the great plains of B: Ayres. but that towards the Eastwards. it verges towards its limits (d) & thus looses its essential characters. —

This opinion is strengthened by the occurrence of large bones. which certainly must have been found in the above beds. —

Parts of the Megatherium have been found close to M: Video (b), likewise between this place at Maldonado at Solio grande. — also I saw a tooth of the Mastodon, from Tala. on the St. Lucia. —

Bones

I heard of great bones near the source the A. de las Vivoras: & some others will subsequently be mentioned. — In the Estancia of the Berguelo on the R. Negro, some years since a flood exposed a skeleton & armadillo-like case; these were washed down

258 verso

(a) at the very edge or end of the cliff I hastily noticed a few muscles (with blue color) between the coarse sand & Tosca. —
I feel little doubt of truth of this
if this was certain it would form a most interesting datum. — but I do not feel sure enough what will afterwards appear, it does not appear to be very improbable. — The muscles were 15 feet above level of constant fresh water of flooded river: muscles same as now existing at M. Video.

(b) I saw these relics at a padres Don Damasio Laranhaia,1 the one found at A. Seco, close to M: Video, was preeminently curious, it was the tail of the Megatherium. — it was only the extremity length 17 inches circumference at the upper broken end, 11- 1/2 inches at extremity. 8 1/2/ whence where it ended in a very obtuse rounded point. — it was very heavy & solid & formed a most formidable weapon. — of y course quite rigid. — the vertebrae were attached to the inside & small in proportion. — there was scarcely any intervals for the fleshy parts. — the outer surface was areolated with small circular patches, a little distant from each other, in this respect & being smoother differing from the common cause. — the intermediate spaces were finely punctured (as if for small vessels for an external skin?).

1 The same person is mentioned in the Banda Oriental notebook, p. 36.

259

1833 (11) The Pampas

B. Oriental

& some fragment yet lie in a muddy pool. —

They were originally at a in the side of a cliff & higher up than at present. at about 20 yards distance I found red Tosca & white calcareous concretions.

(b) look at notes

A few miles from this I visited the site of another group of bones (Toxodon) & Mylodon) & dermal cover on the A. Sarandis they were discovered in a similar manner as the others. — but the cliff, in which they were imbedded was of a white earthy clay: this bed extended for a considerable distance. it may belong to the Tosca or some posterior alluvial formation, but I have no means of judging. —

Bones

(a) I have already mentioned 17 places where I have heard of large bones being found. — in many of them the bones were numerous. — I have also seen several teeth of which I could not find the origin. — When it is considered. that the sites, where these bones have been found, are generally vertical sections made by running water in one vast plain. — it will be seen how prodigious the number must be. with which are at present. & probably will for ever remain buried beneath the Tosca. —

Gran Seco

When travelling about the provinces of B: Ayres, I heard some facts, which may perhaps be explanatory of the number of bones, found in particular situations especially such as in the river courses of Siberia. — The period included between the year 1827 & 30 is called the "gran seco"; during this time, so little rain fell, that the vegetation (even to the thistles) failed; the brooks were dried up & the whole country assumed the appearance of a dusty turnpike road. — This was especially

259 verso

(a) These bones excite very little attention in the country: if a perfect head is found it may perhaps be kept, but in a short time is sure to be destroyed. — From this inattention doubtless very many bones have been entirely overlooked. —

(b) In both these places, the armadillo-like case occurred with the large bones: if these bones are those of the Megatherium then there cannot remain the slightest doubt concerning the envelope of this extraordinary animal. —

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1833 (12) The Pampas

B. Oriental

the case in the northern part of the province of B. Ayres & the southern of St. Fe. — Very great numbers of bird, wild animals, & cattle & horses perished from the want of food & water. — the lowest estimation gives in the province alone of B. Ayres, a loss of one million of cattle. —

One Proprietor (at S. Pedro had previously to these years. 20,000 cattle, at the end not one remained.

San Pedro, is situated in the middle of the finest country & even now again abounds with cattle animals. yet, during the latter end of the "gran seco" live cattle were brought in vessels for the consumption of the inhabitants. — The cattle animals roamed from their estancias & as I was informed by an eye-witness that herds * (a) of thousands rushed into the Parana, whence exhausted by hunger, they were unable to ascend the muddy banks. — The arm which runs by San Pedro was so full of putrid carcases, that the master of a vessel (the one in which I descended the Parana) told me that the smell rendered it quite impossible for any vessel to pass that way. — Doubtless Without doubt some hundreds of thousands animals thus perished in the stream river; their bodies, when becoming putrid would floated float down the stream; & many would in all probability be were deposited in the estuary of the Plata. —

All the small rivers were highly saline & this caused the death of vast numbers in particular spots; for when an animal drinks of this such water it does not recover. —

I noticed, but probably from a gradual increase

260 verso

(a) * note

Azara talks of the frenzy of the wild horses rushing into the marshes during a dry season "et les premiers arrivés sont foulés, et écrasés par ceux, qui les suivent. Il m'est arrivé plus d'une fois de trouver plus de mille cadavres de chevaux sauvages morts de cette façon." Vol I. p. 374. —

1 Azara 1809, vol. 1, p. 374. This note was used in Journal of researches, p. 156.

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1833 (13) The Pampas

B. Oriental

that the smaller streams in the pampas were paved with a breccia of bones. * (e)

Subsequently to this unusually dry period a very rainy season commenced, which caused great floods. (c) The deposits from this cause has probably already covered up many thousand skeletons. — What would be the opinion of a geologist viewing such an enormous collection of bones of all ages & sorts kinds of animals thus covered up by a embedded in one thick or earthy land mass? — 9 Would he not attribute it to a flood having swept down the surface of the the land 2 in [was not] rather than to a common order of things. )

That it is a common order of things is certain (b) for the dates of several other "secos" were enumerated to me; but none so bad as this. —

Proceeding northwards from Colonia, we come to the Sierra de St. Juan composed of gneiss (a), in several places at the foot of these low hills, there were others of rather less altitude, or what might they more properly might be called bits of table land of hard calcareous matter. — the degree of purity varied much, sometimes snow white like chalk, but appearing to contain argillaceous matter; more generally with specks of silex, of & even large fragments of granite becoming in time breccia then again semi-crystalline. with nodules of agate.

also very frequently resembling pure tosca rock: which indeed I believe it to be, only containing more lime, we shall subsequently see it precisely resembles the great plains about B. Blanca &c. — indeed in its manner of scaling degradation & general appearance it was impossible to perceive any difference. — it has the purer parts have been burnt for lime

261 verso

(b) I have forgotten the exact times, but I believe they have occurred at intervals from 10 to 15 years. —

(a) The old crystalline rocks are described in the geology of M. Video, thus keeping the two formations more distinct. —

(c) Hence it is probable that some thousands of those skeletons were buried by the deposits of the very next year

(e)* note

In the neighbourhead of the great towns on the shores of the Plata, the number of bones strewed over the ground, is truly astonishing. — Since our return, I have been informed. that ships have been freighted to England this country with with a cargo of bones. to grind for manure. — The turnip fields in Great Britain being manured That cattle in England should be fattened for on turnips, manured with the ground bones of animals, that lived on in the plains southern hemisphere, is a curious fact in the commerce of the world. — In the East Indies, the luxurious drink wine cooled with North American ice, which in its journey has twice crossed the equator. — The same people may have at their table, fish fresh as when caught taken from the waters of the same country.

262

1833 (14) The Pampas

B. Oriental

but not lately, & its answering seemed very doubtful. These hills beds pass into each other without any sort of determinate order (b); they face or lie on the gneiss & interfold amongst the low hills of the latter rock.

They have been subject to much alluvial action, which has forming valleys at the foot of the harder rocks & has separated a plain into hills. —

The modern formation occurred both on the NW & SE side of the very irregular N & S chain of hills. —

At the Caleria (lime kiln) de los Huerfanos, a few miles further north, we have the same rock, it is purer, harder, whiter, & contains fewer particles of quartz: it is burnt for lime. — A 1/3 of a mile further on there is a coarse (large particles of silex! highly ferruginous bright red sandstone, mingled irregularly with a pale & more earthy sort: This bed we shall see overlies the Limestone (excepting where immediately resting on the old crystalline rocks) & is the most modern in the country. — Proceeding onwards to Las Vacas we occasionally see it peeping out through the grassy undulations, till we arrive at a band of low granite & gneiss hills south of the A. de las 3 bocas; here it lies at the base & on the old crystalline rocks, & the road passes alternately over granites & this sandstone: In the deep ravine of the tres bocas the it lies over a pale Tosca (a) which abounds with calcareous matter & concretions. — & immediately beyond it a knoll of granite juts up. —

The next section I obtained was at the mouth of the A. de las Vivoras; here, as has already been noticed, we meet with the same limestone, as at

262 verso

(a) The sandstone or rather breccia here contains large fragments of quartz & granite. —

(b) It is very remarkable, the number, variety & suddenness with which of the changes, by which these rocks pass into each other: near Mercedes crystalline Limestone is coasted by Botryoidal quartz; proving a degree of chemical action quite unknown in other parts of this great formation; probably there were mineral springs in this neighbourhead. Is it too rash a conjecture to imagine that to the NE of this district in the little frequented country of the interior, there may be at the present day extinct volcanoes? —

؟ The presence of the conglomerate in Eastern part of Province may be owing to the decomposition of the Trappean rock (which they accompany) affording a matrix. — V Porto Praya? —

263

1833 (15) The Pampas

B. Oriental

St. Fe Bajada; the purer sort strongly resembles it. — cellular & crystalline & with numerous impressions of a bivalves which as far as my memory goes is precisely the same in both cases & occasionally with the large oysters — in burning the same time & proportion of fuel is required: —

More generally the limestone is very impure, being nothing more than siliceous particles, cemented in a calcareous base. — the seams of the beds are divided by fine white sand (this also occurs at the Bajada). — There can be no doubt this bed is only variety of those described at St Juan & los Huerfanos. — At Punta Gorda, where this strip of limestone ends on the Banda Oriental side, this bed overlies fine white sand, beneath which there is a bed about 30 feet of pale clay with v several of the large oysters. — p. 19 Beneath this in the vertical cliff there is a bed of red Tosca, with numerous concretionary balls & oblong masses of white hard Tosca rock: again at the mouth of the vivoras Vivoras the river flows over a mass of cavernous pale Tosca rock, which from position must likewise be inferior to the limestone & oysters. —

This red Tosca & tosca rock precisely resembles that of the Arroyos Medio & Pabon &c &c in the Pampas & which as we know contain the bones of extinct quadrupeds. — Before I had seen this important section, I thought the latter animals entirely posterior to the oysters; but now it must remain doubtful; for although the Tosca of B. oriental. which contains the bones is more similar in character to that of the Bajada, which also contains them, than to these

263 verso [blank]

264

1833 (16) The Pampas

B. Oriental

inferior Toscas, yet the circumstances, under which the two sorts of beds were formed have been so similar, that it is not improbable that the same animals existed on the neighbouring continents. — There I was informed at the Bajada that large bones have been found in the Limestone perhaps these were belonged to quadrupeds; although at first sight Cetacea appear much more probable. — I believe this limestone does not form any important division in the Tosca formation, but merely a more calcareous variety of Tosca rock, of which during the deposition circumstances favoured the presence of shells. wh a type of animals so remarkably deficient in the general Tosca bed. — the supposed age of these shells will subsequently be mentioned. —

And it will be the safest conclusion to come to, to believe that the great quadrupeds existed during the deposition of the superior part of the Tosca. — The limestone forms quite narrow strip from Punta Gorda. to the Vivoras; it has undergone much denudation; there is a trace of a similar formation at Colonia. —

A Frenchman found a bed of the great oysters, in the very streets of the city. — he proceeded to work for them but was stopped by the magistrates. — I saw plenty of fragments, they were not rolled & marked with dendritic manganese. — they were said to form a bed. lying close together. — the gneiss must have been be a few feet beneath. —

their position is about 20 feet above the level of the river; I have no doubt, that

264 verso [blank]

265

1833 (17) The Pampas

B. Oriental

this is the only remaining part of a bed, such as the pale clay at P. Gorda.

On the road to the Capella Mercedes, there I passed repeatedly more or less pure calcareous rocks, limestones, sandstones with calcareous base & Tosca rock: also the dark red ferruginous sandstone. — They form horizontal beds & are only occasionally visible in the grassy plain. — their relative positions cannot be seen. — The country being geologically the same as the Pampas of B. Ayres we have the same external features of vast impenetrable thistle beds, without a tree or hill to break the horizon. — Near the sources of the St. Salvador there is a bed of brittle, conch: fracture of white jaspery rock. — marked with dendritic manganese & decomposing to a considerable thickness on its external surface. — in this there are nodules of milky agate. — the bed is on a grand scale. what the nodules were in the calcareous beds of St Juan. — We again passed the Tosca rock, a little granite. Tosca or calcareous rocks & the red sandstone. —

This latter rock is very abundant in the neighbourhead of Mercedes at the Estancia of the Berquelo. — it here forms flat topped hills, with low vertical cliffs surrounding them. These hills ran NE & SW & were widely separated by great valleys, but evidently were once united; denudation must have been carried on in the largest scale:

This rock varies considerably in its characters, it is even sometimes largely conglomerate, but more generally a coarse sandstone & fit to be used

265 verso [blank]

266

1833 (18) The Pampas

B. Oriental

for rough architectural purposes: in the lower part of the cliffs it becomes white with red streaks & nodules, & finally is merely a coarse slightly agglutinated sand. — This bed must generally lie upon Tosca or a gritty white sandstone cemented by calcareous matter. in one place I heard of it as being on a pure limestone, & in another I saw it on a highly calcareous Tosca rock. — I saw this bed 10 miles higher up the R. Negro, we have seen it on Tosca at the R. 3 bocas, & to the South of it. —

also in intermediate patches. — I was surprised on my return to find a small bed of the more compact variety 1548, (was just able to perceive the horizontal stratification) at Las Pietras, near M: Video; it here was incumbent on granite:

In the Maldonado notes, (P 117. & 9). a sandstone & breccia at P. d. Acunar & Las Minas, which I remember to be of the same appearance as the above one. — it occurs on each side of the granite hills. I at that time was entirely ignorant of its age from the absence of stratification. —

The bed therefore extends in a E & W line, extreme points, 162 miles N & S do 100. — We have seen it in the most modern rock, but it is formerly certain that the earthy Tosca which contains the bone in B. Oriental was deposited after it & after its denudation; for what would have removed pieces of the hard sandstone in forming valleys, would have carried away all the Tosca. — I do not however suppose that this rock extended from the Uruguay to Las Minas & that the small bit of at las Pietras is the only remnant but that it was originally deposited near granite hills or other causes favourable for its production. —

266 verso

armour not same as Glyptodon clavipes p. 107 Fossil Mammalia

267

1833 (19) The Pampas: B

B. Oriental

The lower beds in the estancia of the Berquelo, are gritty sandstones, or angular particles of angular silex firmly cemented together, in its lower parts it contains layers of flint, with veins. & a conchoidal fracture. — in one place I saw it separated from the coarse red sandstone by calcareous Tosca & I believe this is generally the case. — Between this place & Mercedes there are endless varieties of this gritstone, more or less calcereous & ferruginous. — near to the latter limestone has been worked from beneath a siliceous bed with much botryoidal agate. — Near to this at the Calera. Daca (a) a fine compact limestone lies on a calcareous grit & is said to be covered by the red sandstone at no great distance. — In sinking wells in this neighbourhead, the flint is lowest bed. — On the road to the Sierra, perika places about 20 miles up the R. Negro. — there is much fine red Tosca with Tosca rock. this must I think be inferior to the red sandstone. — The cliff of the Perika is about 50 feet high. the upper beds are prettily variegated agate mingled with pure tallow-like limestone so that the surface of the latter is coated with a botryoidal variety. — beneath this a conglomerate of quartz & granite — then gritstones. with more or less calcareous matter, one bed coloured a manganese pink. — A thin bed of red Tosca & lastly a highly calcareous gritstone or even limestone; this is contrary to the usual order. when the flints seem subordinate. (b) — From all this it appear these various rocks are only parts of the one formation of St. Juan. Huerfanos. Carmacho. St. Salvador. & that all this is identical with the St Fe Bajada bed.

267 verso

(a) I was told at the Lime Kiln that organic remains have never been seen in this rock. —

(b) I have omitted to state, that 4 leagues to the South of Mercedes (on my return to M. Video) there is much old quartz rock; we then again find the gritstone, granite & flinty gritstone; from this place. (25 miles South of Mercedes) we have nothing but granitic rocks, till we arrive at Pietras close to M: Video). —

((Read what I have written))

cannot understand
certain the way [both] spaces
red-sandstone
[limited] [explanation], age of
lower beds. topic & correction + and I [hear]
or [illeg] calcareous beds probably all of one age
(( Volcanic action)) NNE [illeg] of
Volcanic action
on a [illeg] descended hills
no superficial tosca, but
- lower course plains
with same amounts
as at St Fe above
it limestone.

if [illeg] to this was
to elevate this [illeg]
before [Berquelo,]
we can see how
elevation [illeg] form is denuded
tosca & local white earthy

((Read what...white earthy] in pencil.

268

1833 (20) The Pampas

B. Oriental,

that in this Eastern part it is often covered by a coarse red sandstone; that in some cases it lies on Tosca with much Tosca rock, that in others it is covered by a Tosca with less Tosca rock, that this latter contains numerous bones of extinct quadrupeds. — It will subsequently shown to be probably nearly contemporaneous with the great Southern Patagonian formation. —

At the mouth of the R. Uruguay. where the A. St Juan enters. there are some flat sandy tracks, a mile or two inland & only just above the level of the freshes. — these plains are crossed by low rounded straight lines of sand dunes. such as may be seen when the land is gaining at the head of any great bay. — In this sand are very many bivalve shells (1543) 1543. — These occur all along the coast, at the Agraciado. several miles inland 20 further up the river they are so very numerous, that the sand is sifted & the shells burnt. — I only saw this one sort: it is said there are no others at the A. Agraciado. — I suspect them to be marine (am not sufficient conchologist). if the contrary, all is simple: but if so, it is curious as they are at present at least 50 miles above salt brackish water. — At M: Video there are beds of muscle shells, but so little (20 feet) as to be explainable by change in set of tides &c. — On the South of the Plata at Ensenada shells occur in great abundance beneath the surface of the ground; also near Somborombon; in the former place they are worked for lime; I could not see them from the revolution. —

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1833 (21) The Pampas

B. Oriental

The R. Plata is in fact an estuary: from the above facts, perhaps in former times it was deeper & rather broarder (a) & extended as high up as the most northern of the connecting arms between the Paranas & Uruguay. all which part of Entre Rios is covered by water during the freshes. — The perfection of the shells exposed to the atmosphere is curious & shows that the time proof relative of the water has not been very long established; which circumstance other facts, will be shown to render probable. — The fewness of the banks, & little alluvial land of the Plata, compared to the other great rivers of S. America may perhaps be explained on the same principle. —

B. Ayres

We now return to the Tosca, which great formation extends to the R. Colorado. about 400 miles to the South of B. Ayres. — This plain presents singularly few geolo sections for the inspection of the geologist, excepting where it is crossed by ridges of old crystalline rocks. — Buenos Ayres itself is noticed P. 61. —

(b) it is stated that Gypsum here occurs, this is not common in proportion to the quantity in the pale clayey beds of the more southern parts. —

1558 At the R. Chuila. there are beds of a soft Tosca rock, or hardened Tosca. — on the road to B. Blanca about 25 miles SSW of the capital. I saw a well 40 yards deep (dug during the "gran seco"). it was entirely in dark red Tosca. without any of the calcareous concretions. — At the Guardia del Monte, 3 or 4 leagues north of the Salado, there are some large fresh water lakes; on the coast cliff 4 feet high of reddish Tosca, with vertical calcareous stalactiform masses of Tosca rock & concretions of paler, harder, fond capillary vesicular Tosca imbedded in its mass. —

269 verso

(a) All this is the merest conjecture because I do not know whether the shells are of marine or fresh-water origin. —

(b) Ignat: Nunez1 states that 75 feet beneath the surface Tosca hard Tosca, containing lime is met with. (evidently my Tosca rock) This is as I should expect — I was surprised at its apparent absence in this neighbourhead

Have seen Mastodon's tooth from the Salado

Bones

1 Ignacio Benito Nunez (1792-1846) it is not clear to which of Nunez's works Darwin refers.

Have seen...Bones] in pencil.

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1833 (22) The Pampas

B. Ayres

I here found, part of the armadillo-like case of the Megatherium; to it was attached a mass of Tosca proving its original position. — on the shore likewise I saw various small fragments of bones. (a) — & various many people told me of the frequent discovery of "giants" bones. — At the pass of the R. Salado there is white clayey Tosca. with much Tosca rock. — This river is known all over the country for the number of bones found in its course. — I have seen a Mastodons tooth from it. — & I have already stated my reasons for decidedly thinking all these bones were originally imbedded in the Tosca. — I am informed there is much crystallized gypsum in certain parts of the cliffs. — This river in the summer is very low & the water highly saline. — Travelling southward nothing more is seen of salt water or Salinas till near B. Blanca. — Its sources are in the salina lakes, which also seem to feed the smaller streams already noticed which flow into the Parana. — It may perhaps be suspected, that all the salt is originally due to the great sterile Travesia (abounding with salt & spiny bushes) which extends between the cities of Mendoza. San Luis. Rioja. St Jago Cordoba. Tucuman. — (Miers Chili). —1

To the South of the Salado (or indeed of B: Ayres) & extending to about 30 miles NE of the Sierra de la Ventana. the country has the same general features; moist grass, plains with a blank vegetable earth, passing into swamps with coarse herbage & bog earth. —

1 Miers 1826, vol. 1, p. 235.

270 verso

(a) I cannot find that this specimen is numbered; (without it is (1408). — Is easily recognizable; being the most perfect & largest piece I have sent home, about one foot long & 6 inches broard. —

271

1833 (23) The Pampas

B. Ayres

& extensive, but shallow lakes, flanked with great beds of rushes & other aquatic plants, which afford a harbor for innumerable wild fowl. — This country clearly forms a part of the "cienegas or grassy swamps". in Miers Chili. — It appears to reach to the in a NW direction to the foot of the high table land or Travesia which extends from Mendoza to San Luis then to Cordova. — It is a basin or low tract of country very imperfectly drained & may be likened to the Cambridgeshire ferns. —

I will pass over in order the few places where the formation can be seen: — 30 miles to the South of the Salado there is seen a little Tosca rock: 90 after riding 60 miles more near the Indian settlement of Tapalguan, there is an abundance of fine Tosca rock, marked with dendritic manganese 1556 1557: in general appearance precisely resembles that of the streams into the Parana, some of that at St Juan. & as well will be seen that of the plains of B. Blance. — in many places it forms small rapids or waterfalls & is seen horizontally overlying pale Tosca. which contains nodules of harder, darker coloured Tosca. in the same manner as at the Guardia. a reddish Tosca contained paler. — On the banks of the R. Tapalguen for 2 or 3 3 or 4 miles to the South of the settlement there is the same Tosca rock. —

In about 30 miles more the road passes the Sierra del Tapalguen. This is a range of low (200 300 feet?) hills of quartz rock. which generally is white & rather granular. — On the North & South side of these hills were small pieces of table land, higher than

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272

1833 (24) The Pampas

B. Ayres

plains & composed of calcareous Tosca rock, & exactly like the great. B. Blanca plain. — The beds abutted horizontally on the hills, but were narrow on each side of it. —

(b) This quartz range commences at Sierra Viculcan (pass on gap, Indian language Fr) near Cape Corientes. it runs according to the map (& this cannot be more than a point wrong) in a W 15° N. direction & extends about 150 miles across the country. — The hills, where I saw them, were of a remarkable shape, but the summit the one which I ascended was oval & quite level on the summit, it was surrounded on all side excepting a southerly pass, by a cliff of 15 to 20 feet high, so that it was necessary to return by the same route, which I ascended by. — the diameter in this was not more than 150 yards; but I saw others apparently of same structure & much larger. —

I could perceive no clear stratification or a cleavage when sailing past C. Corrientes I saw the Sierra Vuulcan. it consists (P 49) of square pieces of table land. sloping on their southern front. — at that time I had no doubt about their being outlying patches of some modern bed. — A Gaucho who accompanied me, said the rock was reddish but quite as hard as hence, & that the white pieces were sought for striking fire.

He called one the Comb, for which purpose it is used, the surrounding cliffs are about 30 or 40 feet high & quite perpendicular & the diameter 2 or 3 miles. — Falkner says this is the first true rock & gives a curious account of the Indians driving wild horses within & thus guarding the entrance, having them secure. P.70 Falkner's Patagonia —1

It is a curious form for an old crystalline formation (a)

1 Falkner 1774.

272 verso

(a) To the West of the Sierra de la Ventana, there must be a hill of the same description. but on a greater scale. — A soldier informed me, that in the Indian wars a party drove up their horses &c to the summit, where there was water. & that there being only one place of ascent, the Christians, although nearly 1000 strong could not touch them. —

(b) 30 miles to the North of the Medole of this Chain of Tapalenon, I see in the maps Arroyo de los Hesos (or bones). it is probable that large fossil have there been found.

Bones

273

1833 (25) The Pampas

B. Ayres

About 100 miles north of this Sierra, I see in the maps, another called La Cervillada. it commences about 60 miles to the West of the Eastern termination of Tapalguar & run in a W 27° N direction for about 100 150 miles. — I should think, that this range arising in so undulating a country, must be of same geological age with the more southern & nearly parallel one. — (it must be remembered that their directions in such imperfect maps mean no more than that these hills running between E by N & W by S & NE (W by N & E by S) & (NW by W & SE by E). —

Leaving the Tapalguen. before arriving at the Sierra Guitru-gueyu, we pass 60 miles of country abounding with lakes & swamps. — In this, like islands, there were four or five small dry spots where there Tosca rock might was just exposed to view. — At the foot of the Guitru-g there are some extensive plains of alluvium; these are so level, they probably were formed beneath water. — Perhaps much of. On the edges of the Sierra, there are beds of Tosca rock in form & nature resembling those of Tapalguen, (1553) & therefore above the plain. (a) —

The Sierra is composed of many parallel rows of hills, whose extreme point is where I crossed them; they range about NW & SE. & thickening out, form a mammilated country for the whole distance (23 miles) between this main chain & the Sierra de la Ventana: — They seem to run far into the country in their NW line. — Their altitude is about 500 feet above the plain. — in general appearance, strikingly resemble the most lofty chains near Maldonado. —

In several places, where I visited them, they consist of nearly the same rock, viz. a feldspathic

273 verso

(a) So called from a streamlet of that name, which enters R. Guègon. —

273A

North of Cape Corrientes

sketch in pencil on heavy white paper with pale blue watercolour for the sea.

274

1833 (26) The Pampas

B. Ayres

1554. 1555

one with specks of mica (1554. 1555) 1554. 1555. — Without any marked line of separation, on the summits of the hills there was a pale & reddish purple slate, not very fissile: cleavage running NW & SE or rather NW by W & SE by E; dip southerly or vertical.

From these hills to the Ventana, the road skirts the SE extremities of the many hills. & lies generally over calcareous Tosca rock: Here we have a change of vegetation, the light calcareous soil only supports a long brown fine gneiss instead of the greener & more coarse vegetation of the swampy plains. — This is the character of the great B. Blanca plain, & whenever the Tosca rock forms a continuous bed. —

The Sierra de la Ventana primarily consists of a narrow steep ridge, the highest part, being four rugged points, attains an elevation of between 3 & 4000 feet. (angular measurement C. Fitz R.).3500 (1840) The chain, viewed from the highest part appeared to run in a NW & SE line; but at the SE extreme point (where the road crosses) the lower hills were (W 25 N) & (E 25 S). 3340 Fitz Roy — The strata, or cleavage ran NW by W & SE by E. & generally dipped to SW by W at ∠ 45° or more. — To the NE there is the maculated plain: which connects this range with that of Guitru-g. (a) to the SW there a few parallel lines, formed of detached hills. — to the NW I believe the chain of this Sierra continues for 20 or 30 leagues. — The mountains consist of laminated quartz; generally white & pure, but sometimes tinged reddish. — I saw in places some taleose slate with tortuous cleavage

3500
1840

3340
Fitz Roy

(a)

274 verso

(a) Now, that I am on this subject I may notice, that a soldier informed me that N. of the Colorado & far in the interior in sight of the Cordilleras the country is mountainous, (hills about half as high as the Ventana). the rock being hard & grey; the ridges travelled towards the Cordilleras (or somewhat near E & W direction)

275

1833 (27) The Pampas

B. Ayres

These great masses of quartz rise out of an apparently horizontal plain of calcareo-Tosca rock, which not only abuts up against the hills, but interfolds & separates the parallel ranges. —

V. Journal
The mountain has a strange & desolate appearance: The Tosca rock plain, extends on the Southern side as far as the eye can range; about 5 4 leagues distant, the plain is about 200 feet above the level of R. Sauce (which is deep & rapid) from this to the foot of mountain I could perceive no rise; yet from the cold I experienced during the night, it probably is several hundred feet above the level of the sea. —

The horizontal beds are all of one kind, a hard. calcareous Tosca rock, which I believe in some cases covers a reddish Tosca:

It is very remarkable, that in this whole plain I did not see a single fragment of quartz, untill within 1/2 a mile of the mountain. this forms a strange contrast, with so abrupt so broken a mountain as the Ventana; its very central ridge is divided by a horse pass, & its sides are worn into the steepest ravines. — in former days many a storm has dashed the waves against this rugged island. — I was much surprised to find nearing foot of mountain a bed of Tosca rock containing pebbles, with horizontal water lines (or slight variations in tint) lying over a mass of Detritus; We may from these facts infer, that during the ordinary course of wear & tear, a calcareous sheet was deposited, & that this was immediately & quietly upheaved, so that

275 verso

Discuss whether Quartz plates are strata or cleavage

276

1833 (28) The Pampas

B. Ayres

neither at that period, nor subsequently has any alluvial substances been washed over the plain.

Close to the base of the hills there is some earthy alluvium. containing fragments. of Tosca rock & land shells (Bulimi). This must have been formed. during present circumstances. — In two or three places on the sides of the mountain, I found at an elevation of 3 to 400 feet above the level of the plain, a coating of rounded pebbles & fragments of quartz united by a ferruginous base & coating, in a bed, the solid rock. — This pudding-stone. was tolerably hard & resembled those which now form on coasts, I look at this as the line of a former coast.

In this country we first meet with salinas which will presently be described. — From the Ventana to the foot of Bahia Blanca, the plain of Tosca rock is in some most places covered by sandy earth it is traversed by some gentle valleys & there are depressions, with no exit from them. — Specimens (1551. 1552) 1551. 1552 are examples of Tosca rock from near Bahia Blanca. — it oftentimes is marked with water lines (b), is occasionally semi-crystalline & seems to contain minute extraneous particles. —

Following the road across the basin, formed of saltpetric swamps, sand dunes, & detritus plains, in which the fort of B. Blanca stands, we come to an a cliff of Tosca rock. — In this valley I last saw a fragment of quartz rock, a distance of about 25 miles from the nearest part of the Ventana range. (a) — Ascending the above cliff at a place long called, the Caboza del Buey

276 verso

(a) The beach all along the N. coast (distance?) of the Bay of Bahia Blanca has rounded quartz pebbles. — ascertain distance

These must have come from the Ventana, but previously to Tosca rock bed. — perhaps imbedded in such formation, as M: Hermoso & P. Alta & now again made free. —

(b) This plain I estimate at 200 ft above the swamp; besides a plain of 30 or 40 feet of on which the town stands; the edge of the escarpments showed in many places this appearance which perhaps indicate other plain: [sketch]

It strikes the me, the 40 foot plain is perhaps only the superior one demanded; & that the lowest beds in all parts contain particles of silex. —

277

1833 (29) The Pampas

B. Ayres

we come to a plain, of about 60 feet elevation above the swamp, into which during gales, a little brackish water is forced. Upon the edge of the cliff, there is a W & E range of high sand dunes, which run for some miles across the country. — The plain is rather undulatory, & judging from the holes of the Agouti is composed of Tosca rock, like the cliff, beneath a little soil. — Twenty miles to the South, there is a remarkable (W by N) & (E by S.) ridge; it is formed by square topped pieces. separated by large gaps or valleys, & is about 150 (?) feet (conjecture) above the plain & therefore perhaps has same elevation with great B. Blanca plain. — its summit is composed of hard Tosca rock 1550; which varies from one to several feet in thickness: at one place this rested on red. clayey Tosca, which again was on a pale variety. — This was near top of hill; at the base there was a well in red Tosca. —

At the southern base (a), there is a band, about 8 miles in width, of lofty sand dunes, which run parallel to the ridge. — These hillocks, precisely resemble those now forming on the coast (for instance at B Blanca) & in like manner are separated by level plains. [sketch]

The sand is well protected by vegetation & I could not see any shells. — To the South of them we come to a level Tosca plain: which I estimate not to be more than 40 feet above the level of the R. Colorado. — The sand dunes resting on this clayey bed, formed small pools, a most insatiable resource in this arid

277 verso

(a) These sand dunes stretch in same direction, for many miles to the westward & to the East till they join the coast.

I can only suppose this remarkable ridge in such a country, was formed by deposition over quartz line running in its ordinary direction. —

State Reason, after describing the marginal elevated patches on sides of other chains. —

I can ... direction.] in pencil.

278

1833 (30) The Pampas

B. Ayres

country. From southern edge of the sand hillocks to the Colorado, 20 miles; in this I obtained only one section, where a well had been attempted. — Sandy earth with porphyry pebbles (3 feet) (these pebbles will subsequently often be mentioned) & lots of white Tosca rock: white calcareous, semi-rocky Tosca. with dendritic manganese, 2 feet. — the rest of well all red Tosca. —

This was the last section I obtained in the great Tosca formation; but I believe it to cross the Colorado, & from thence (judging from the Gauchos description of nature of country) to extend in a SE line & to include the islands south of the mouth of the Colorado. viz from Guam. Deer & island. —

This country generally has same appearance as mentioned of the great B. Blanca formation plain; South of the ridge however we meet with some spiny bushes; but I imagine this is solely owing to its proximity to the sandstone shingle plains of the R. Negro. — (where such bushes are universally present): — I may here notice one curious fact, which seems too general to be accidental, viz. the height. & cliff-like border of Tosca rock, round the ridges of crystalline rocks. — viz. northern side (especially) of the. Ventana, of Guitra guigu, of Tapalguon, of St. Juan (In B. Oriental). — from its horizontal, unbroken form.

It is impossible for a moment to imagine these lines of elevation; but rather being elevated points in the ancient sea, the calcareous-argillaceous deposit was in proportion, higher than in other parts; & that its sub cliff-like edge. has subsequently been formed as will be described. —


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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)

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