17

30

1833 B. Ayres          Rio Negro (31)

The Pampas &c

The age, period of elevation, form of land of the Tosca formation will be noticed, after the R. Negro, with which it is intimately connected. — I will commence with the S. Barranca at the mouth of the R. Negro &. so return to the Colorado. —

R. Negro

These cliffs are about 120 200 feet high, they are mainly composed of a greyish-blue sandstone 1531 (a), which varies in hardness from almost loose sand to a pretty hard rock. — It alternates with white soft sandstone & in same bed the color changes in curious angular patches. — There are narrow beds or layers of hard. true sandstone 1530.

in one place these beds reposed upon a rosy glowed clay, which again was on a ferruginous sandstone. — About 2/5 up the cliff, there is a bed of true red Tosca 1532 (b), & above this a narrow layer of white pure Tosca rock, most curiously abounding with moss-like marks of manganese. 1534 —

Again we have sandstone & ten another narrow layer of [striped] gritty Tosca rock. — In the Tosca there is some gypsum, but not abundant, it obscurely affects the horizontal plate, so frequently to be seen further to the south. —

[does] d'Orbigny gives thickness of gravel

I found also one Anomia (1540) 1540 & some hollow impressions of a bivalve in the Tosca. — These were the only organic remains (The bivalve resembled an Torcardium. I believe it was the same which is found at St Josephs). — Amongst the beds of sandstone was a narrow one 1533, of calcareous matter (c).

All the beds were horizontal, but the sandstone was divided into curved, highly inclined plates. supposed to be from currents. —

17 verso

(a) The sandstone generally contains small stalactiform, linear cylinders of a darker, harder sandstone

(b) The Tosca bed thins out to nothing. —

(c) I have omitted to notice, that on the beach there was much sandstone conglomerate with Pumice pebbles 1535; I could not find the bed, which was unfortunate, as it would prove the action of active volcanoes, during the Deposition of the sandstone. —

Also I have omitted, that in the settlement, many of the layers of sandstone are highly saliferous; this is curiously seen in the cuevos or the cellars cut in the rock, which glitter with fine crystals of saltpetre, when a candle is brought in; also when the rock has been plastered, in certain layers, during rain, the plaster always falls of & the sandstone crumbles away & is damp from some saline substance.

18

1833 (32) Rio Negro

The cliff sandstone is every where covered by a bed (12 feet thick ?) essentially composed of calcareous matter imbedding pebbles. pure? — The calcareous matter in many places forms the greater part of a nearly solid, semi-disintegrated mass. — From extraneous matter & small pebbles strikingly resembles coarse "mortar". 1537 — The pebbles are generally small, & well rounded; they consist of (mainly) dark coloured feldspathic rock, more or less porphyritic with quartz & feldspar in small crystals. — They precisely resemble those found at St. Joseph. bay & many degrees further south; they have been already noticed to the north of the Colorado. — These pebbles are often times white washed & loose, as I saw volcanic ones at Port Praya. — Some miles to the East of the settlement, I was shown a pot, where much gypsum has been dug out (for housing & white-washing houses) out of this gravel. it occurs in crystalline concretions 1539 from the size of a mans fist to that of his head. —

This gravel bed is a curious instance of mechanical & chemical action. — Whenever I examined the formations, this gravel bed was the superior one. — 15 miles up the river & therefore about 45 west of the South Barranca. —

The sandstone continued of the same soft [illeg] nature, with current cleavage; I then noticed a bed. 3 or 4 or 5 feet inches thick of white, soft calcareous matter, somewhat resembling chalk. 1536 — This was low in the sandstone; there was also another bed of common red Tosca. —

Proceeding north-ward to the R. Colorado, in the first 48

18v [blank]

18A

Sierra Ventana

High plain

lower plain
Pueblo

Abaxo
marshes
saltpetre brackish

[sketch]

Tosca Camp

[sketch]

Tosca camp
(lower?)

diluvium
Colorado
diluvium from the Sea
Salem salt
Pampas

Saliferous sandstone
low camp

High Saliferous Plain

Negro

[right hand side, map:]

Settlement
Bahia Blanca

False Bay
Green bay
Brightmans bay
supp^d Encampment

Rio Colorado
Union Bay
Stone Island
Greek Island

Approximate scale Latitude 40

Bahia e todos los Santos
Deer Island
Stag Island
Bay of St Blas

Pt. Rasa

Rio Negro

Along the right hand side there is a map with captions not in Darwin's hand.

18A verso

Map

Bahia Blanca

19

1833 (33) Rio Negro

miles, there are scarcely any opportunities of seeing the nature of the formation. — There was present however the "mortar" & the pebbles (perhaps however in rather less numbers. at the Poro punero, there is some of the common sandstone & red Tosca. — There are many some valleys more than in the Tosca rock formation (a); & there are likewise depressions, which must originally, or before upheaval, have existed; as no valley or slope can explain in all cases the action of water. — In such depression, there often are the great salinas, or natural salt pans, which are especially abundant in this formation & will probably be described. — The country wears one aspect, viz an undulating, most arid plain, with little brown grass & covered by low spiny brushes. — there are many sorts of bushes but all bear formidable spines.

At the Poro secundo (or second well), the plain terminates, abruptly in a broken cliff. — which seeks to run along the country in a NW & SE line; at the foot of this, perhaps 60 foot lower, there is another plain with usual aspect: in the one section I obtained, there was the blue-grey soft sandstone & some Tosca. — *

I did not however see any mortar, only loose pebbles, in fewer number, as on the low Tosca plain north of the Colorado. — In about 12 miles, the plain gradually lowers, till it becomes more fertile with no bushes & greener pasture.

This extends, as already has been noticed to the SE & is either alluvial or Tosca plain. Is the

19 verso

(a) There is one very large valley. about 10 miles north of the settlement, which can be traced down to the coast near to P. Rasa.— (Gauchos say so) — They believe with little trouble that the R. Negro might be turned so as to run enter the sea by it. —

20

1833 (34) Rio Negro

North, we see no more of the sandstone. —

How far to the South this formation extends, I know not; North of San José. (70 miles to S. of R. Negro) we have the great Patagonian bed with oysters. — To the West, it is probable, this sandstone extends very far. — I believe to Churichoel, 70 leagues up, the river. — the external features of the country are said to be in the interior the same. —

Upon reading M^r Miers account (a) of the Travesia of San Luis — Rioja — Cordova, or, which borders the true grassy pampas; its arid saline nature, its sandy soil, & its continuous thickets of spring bushes. — it strikes me that perhaps it is the same formation with this sandstone & even united with it. —

With respect to the age of the "mortar" or gravel, it will subsequently be shown, that after being spread out at the bottom of the ocean, there was time for a few shells such as now live, to be scattered over it & then the plain whole event of Patagonia was uplifted. From the unbroken unworn state of the Tosca rock plain, from its overlying detritus. I think it must be as modern a deposit. —

indeed it appears to me almost certain, that the same calcareous matter, which formed the Tosca rock, mixed with pebbles formed "mortar".

Indeed I do not see where else the lime was to be procured. The electrical actions shown by the Gypsum widens this more probable. — As to the Sandstone itself, judging from the included layers of calcareous matter, Tosca with gypsum, Tosca rock with manganese, I cannot believe the age (or time of deposition) to be very different from the great Tosca formation; perhaps a little anterior; but the variation

20 verso

(a) All the Travesia land, when irrigated is remarkably fertile. — At R. Negro in the low lands which are flooded every year, corn has been produced with an immense percentage, without manure for 30 years successively. — This is another slight argument for their the identity of the two arid plains. — N.B. It is said, water & oranges musk melons ( [illeg] ) in irrigated

It has been stated (b), that the climate (s. productions) in the Southern hemisphere in any latitude corresponds to one 10 degrees higher in the northern. —

R. Negro is situated in Lat: 41°. — the following vegetable productions are raised there. Peaches, Nectarines (of course standard) Quinces, Apples, Grapes, Pumpkin, Water & musk melon, Cherries; Patacas dulces (sweet potatoes), olive, Fig, Oranges (only lately tried) & Indian corn. — Could such trees be raised in Sussex in Lat: 51°. —

A p. 32 metals sublimed

R. saline nature of America connected with recent elevations & therefore mulonic rocks? Mem. sulph. of soda
Daubuisson in do vol II p. 482 —¹

NB. Sr W Parish² states that lakes fresh water is found by digging of fresh water ocean near great salinas? Does not Pallas say do?

Malte Brun³ on Siberia must be read as well as Pallas⁴

In do [illeg] account published by Ingeles. It seems clear that in digging near salt lakes within few yards fresh water found

Under Melisune, where whole country covered with saline matter, water found by digging beneath [illeg] Iquique

Linn Transact vol 8 p. 288 Salt killed all trees too!⁵
[illeg]
See extract from D'Orbigny
Cont salinas & salt fresh Bahia Blanca

¹ Aubuisson de Voisins 1819.

² Parish 1839, pp. 122; 170.

³ Malte-Brun 1822-33, 2: 393-94; 399-400.

⁴ Pallas 1802-3, 1: 283-84.

⁵ Salisbury 1807.

21

1833 (35) Rio Negro

in constituent parts I attribute more to difference of circumstances rather than of age. Nearly coeval then in age, there can be no reason for supposing the Tosca rock part of the coast was elevated at a different period from all the rest of the great southern formations: — Therefore within a time during which shells of the present day have retained their animal matter color. — If we apply the theory of numerous successive elevations, which D^r Lyell has so strongly supported, it will perhaps so well explain various appearances, as to render it highly probable. — I have conjectured, that the elevation height of the Tosca rock round the mountain ridge, was owing to original deposition; they It would therefore first emerge from the water. — Hence we have its cliff like edge. — the beds of alluvium or the lower plains & entire absence on the upper; we may conjecture, that at such a period the M: Hermoso (V. notes of B. Blanca) beds were formed, & that the animals, whose bones we find in groups, lived on such two this first upraised land.

This generally perhaps is the case, with the superior Tosca, of the northern part of the Tosca formation.

In Between R. Negro & Bahia Blanca, there is a remarkable sort of valley in which the Colorado flows. —

Its southern side is the sandstone cliff, where the plain suddenly alters its height. — The northern is the ridge capped with Tosca rock, at the foot of which is a low Tosca plain, as on the other side there is a low one of sandstone. — This valley is about 53 miles broad. — The (8 miles broad) band of parallel sand-dunes with flats between ridges on northern border, in my eyes prove

21 verso

[sketch]

The elevation of beds is caricatured

Proportional breadth nearly accurate

High sand plain
R. Negro
High sandstone plain
Valley of P. Raza
Low do
R. Colorado 20 miles from sea
50
Low Tosca plain
30 to 40 gneiss
Sand-dunes
Tosca rock ridge
Tosca plain
Sand dunes
[illeg] or head of B. Blanca
Great Tosca rock plain N & B Blue

22

1833 (36) Rio Negro

that this was once a beach, by sand dunes, collected by the southerly winds: I look at this valley, as an aestuary, where the Colorado entered, before the land attained its present total elevation. —

The low plains on each side, are I should think 30 or 40 feet above the Colorado, & this river at this station is rapid & about 21 miles in a direct line from the sea. — My chief surprise, is at there not being a great accumulation of Detritus; we have only have a sandy soil with some Porphyry pebbles. — The ridge, which forms the back of the sand dunes, — is to me quite inexplicable; I have seen nothing like it any other part of the country. — I am lothe to think it a line (when the whole plains have been upraised) of elevation. — it is a most vague conjecture, but it is possible there may be a ridge of crystalline rocks, running in their usual WNW course, which cause the cap of Tosca rock to be higher, than the rest of plain. — otherwise it must have been a reef in the sea. worn after the very first elevation. — The great valley, which runs towards P. Raza — I am inclined to conjecture might have been the old course of the Negro, now altered by some upheavals. — In my B. Blanca. notes I have given reasons to show, that there has been one very modern & slight upheaval; sufficient to lift beds, formed in shoal water, only a few feet above it. at That probably beds like those of M: Hermoso had previously been partly elevated, & bones from the wear of which, formed had helped to form these most modern beds. — These various upheavals, will be more readily believed (a), when it is remembered, that they are supposed

22v

(a) to have taken place in a country; a few degrees to the north of which & 600 miles to the West such phenomena are at this very time occurring.

All of which, put together, may be considered to prove that the country was not elevated at one exertion of subterranean force. —

23

1833 (37) Rio Negro

Salina

The whole of Patagonia abounds with Salinas, or salt lakes. This cause will for ever render the greater part, uninhabitable by man & those animals which require fresh water. There is very little water of any sort & excepting some superficial pools, which remain after rain, it is all more or less salt. — I have seen salinas in all the three main variations in the Patagonian formations. At Port St Julian, they are frequent, as at St Josephs, where there is the great Oyster bed.

804 Tin label
brackish water at Desire 781 not tin
[illeg] estuary

In the R. Negro sandstone, they are especially abundant. — I saw one small one in the Tosca rock, north of B. Blanca. — 762 Tin label the Salinas chiquatas (SE of same place) & the great Salinas. West of the Ventana, to which in former times, a great large party annually proceeded from B. Ayres to procure salt. must likewise be in the Tosca rock. —

They are generally (strong exception C. Blanco) shallow & the bottoms reddish or black mud; in summer when partly or entirely dry they present a field of snow white salt. — The salt from the R. Negro, whi not much valued, for preserving meat, it causes it to be red, & tough, it is estimated at nearly 50 percent less value than the C. Verd sea-salt. — All, which I have seen, occur in circular or irregular depressions, from which no valley proceeds sufficient to have scooped them out. — They are at various elevations above the sea. — (a) I imagine the depressions are only connected with the salinas, in as much as giving rise to the few (saline?) springs, which this level country can boast of & collecting in winter the rain water. —

23 verso

(a). Perhaps these depressions, were caused during the elevation of these plains: we see that the gravel covers them, as in other parts. —

Some such depression perhaps caused Bay of S. Joseph. & New Bay. —

750 diameter

more 10 = .393 inches
24
1965
786.
9.825

24

1833 (38) Salinas

One salina, which I visited at the R. Negro, is 15 miles up the river & 3 or 4 from it. About 300,000 fanegas of salt are annually raised into the little hillocks on the side of the lake; its export is the principal source of wealth to the R. Negro. —

It was winter, when I was there, & the lake only contained brine; it is very shallow, about 3 feet deep & the water rather reddish. In summer, there is a field of salt 4 or 5 inches thick, (759 tin label) but in the central parts (which are not worked, on account of difficulty in carrying salt over the muddy bottom) it is thicker. — In length it was 2&1/2 miles & in breadth one, is seated in a gravel depression. 5 or 5 miles across, & surrounded on all sides by the high level plain, excepting towards the R. Negro, in which direction the depression lowers itself. — at the head of it & in the deepest part lies the Salina. —

Perhaps the level of its bottom is about 40 feet above the R. Negro. — The bottom of the lake is composed of black, muddy and (a), with a fetid smell (760 tin label) which where it can be seen reposes on the mortar & porphyry pebbles. — The depression therefore is very ancient & before upheaval of the land. — In all the neighbouring country we have the regular soft sandstone. — When I was there, the lake was beginning to decrease from evaporation; on the muddy sand, there were many long slender crystals of sulp of soda (?) placed cross-wise (763 tin label). The Gauchos call this the "Madre del Sal." — There were also groups of numerous distinct, large

See the Falkland notebook, pp. 96a- for disscussion of this expedition on 8 August 1833.

24 verso

(a) On the edges of the lake, the source is highly saline, & a bright green colour. — resulting doubtless from the remains of [Conserve]. — the decomposition of this substance gives probably to the muddy sand its fetid odour. —

Although the water was almost in the state of brine, I saw the marks or burrows of worms or rather Annelidae. — & this is further proved by the number of Flamingoes, which live & breed here, & were then of wading about in search of food. — What becomes of these animals, when the lake is dry; they must actually live in the mud, impregnated in the fullest degree with brine. —

The bodies of the flamingoes are found, perfectly preserved, in the solid salt. —

Nature has created animals for every circumstance we have seen animals inhabiting brine; & the surrounding banks, without a drop of fresh water are burrowed by numerous Rodentia. —