RECORD: Darwin, C. R. Geological diary: Iquique. (7.1835) CUL-DAR37.677-684 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Kees Rookmaaker, edited by John van Wyhe 10.2012-3.2013. RN1

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Where pencil was used instead this is noted in the textual notes. Marginal notes are here integrated into the text.

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

See the introduction to the Geological Diary by Gordon Chancellor.


677

1835. July 13th & 14th Iquique — Peru. Lat. 20°.13' 1

The town is seated on a little plain at the foot of a lofty escarpement (a), which extends far to the North & South. This wall of rock attains a height of about 2000 ft. to 3000 ft (b). As in the Valley of Copiapò the sand has been blown up to 2/3d of this elevation & conceals the nature of the rock formation. — There are in parts distinct appearances of stratification — The lower rocks (as far as my very limited time permitted me to observe) chiefly are composed or reddish & purpleish fine grained crystalline rocks. some of which have an laminated structure. 3041 — Higher up there is an abundance of compact red & purple Porphyries. with more or less numerous crystals of white Feldspar.

I saw a few fragments of a common red Breccia, whose fragments were closely united. — From the stratification, & the close resemblance of the crystalline & porphyritic rocks to those of Chili, It seems probable that this wall is composed of ancient subaqueous Lava separated by some little few sedimentary beds. — This, as compared to the South is remarkable as the only instance where such this formation (corresponding to Porph. Breccia) abuts on the sea-beach. — It explains however the abrupt inland escarpement with which this formation is seen frequently to commence overlie the Granites in Chili. —

As I have remarked, the stratification is not very distinct, but it does not appear highly inclined

677 verso

(a) This plain which is nearly 2 miles wide is of crystalline rocks covered by loose sand — it slopes up to the great Escarpement. To its foot perhaps 150-200 ft. there are many shells with the sand. — As it is certainly possible that such might be blown up by gale of wind. I did not measure the height

(b) Low point where road passes. 1903 ft Barom: here the alluvial or Infaceous deposits reach the edge of the escarpement.

from the angular measurements give 2340 & 3000 ft.

(a) At the time I suspected the presence of these slides to be owing to elevation. — I see M. Dessalines D'Orbigny states such are found at an elevation of 100 metres at Colija, no great distance to the S. —

678A

Mr Bollaert

Granite of coast. Iquique

— Istanga = Volcano = near Iquique

Trinapal

Mr Bollaert in MS. says Guartagaga & Santa Rosa veins they generally run E to W with a little variation but the principal vein NE by E & SW by W — (generally towards NW)

Gold vein near summit of mountain
Iquique
on approaching coast. — less sublimated calcareous [opal] in veins

678A verso

Mr Bollaert

[sketch]

[illeg] of silver irregularly stratified with detritus & sand

See Therna is missing review on tops of veins being level

bent metallic veins

Panizo

Geolog. Proceedings Vol II p. 598

1 Bollaert 1838.

678

1835 (2) Iquique

Hence I believe the The silver mines of Guantajaya, which are situated a little way to the interior just at the back & upon this escarpement. The main rock is a laminated very pale purple aluminous limestone 3037, which I believe is associated with a fine purple sandstone.

The numerous metallic veins are either siliceous or of Carb of Lime with pure — muriate — (& the blue Lead-like) silver. — They have produced immense quantities & have long been worked. — The mountain is covered with a hardened mass of small angular detritus, in which are broken masses of silver ores veins & numerous silicified shells.

There are chiefly striated Terebratulae, & Anonica? &c. 3038: 39: 40: —

There are in the same strata as those of Copiapo — & there is a close resemblance with between the laminated calcareous & arenaceous rocks of the two varying silver minerales. —

In both the formation is that which overlies the main mass of purple sedimentary & crystalline rocks. The mineral of S. Rosa appears to lie in same class of rocks.

From this district I proceeded over an undulating country without any very great descent ascent to in an Easterly direction to where the Nitrate of Soda works, a distance said said to be from the coast of 14 leagues (a). On the road the formation is very much concealed by a singular alluvial covering which will be described. In the few places where I could obtain sections, they are were chiefly laminated calcareous & arenaceous rocks with some few Lavas or beds of crystalline rocks.

The main point of interest is an extensive formation of Rock Salt, & the

678 verso

(a) Probably 25 miles

40 / 3/4
19 / 3/4
20 / 3/4
81 / 1/4

1 1/2
4 1/4
5 3/4

1 1/4
3 1/2
4 3/4

679

1835 (3) Iquique

general resemblance of the strata with those varying kinds which in the whole North of Chili accompany or overlie the Gypseous formation. — In one pit, where the beds are broken up & dip to different points W & S, & at varying ∠s some of which are considerable. —

I found various rocks stratified in the layers. which are represented by specimens 3027 ... 3036. —

I do not know the exact order, pale brown or yellowish. (like Copiapò) slightly calc hard sandstone (3031. 32) was associated with softer aluminous & sandy mixture abounding with rock salt; The salt generally occurs in thin layers & the stone is of a yellowish-green color. — I saw one layer nearly 2 inches thick which thinned out at its extremities. — The stone in many places was very hard, although chiefly composed of salt layers. —

These strata were generally capped by purplish or reddish harder strata of very calcareous sandstone or impure Limestone 3129 (& some dark red sandstones 3030?), there are some thinly laminated white sandstone non calc: 3033 & shattered purple sandy clay-slates. Black Limestones 3034. — There was one mass, 3 or 4 yards thick, of a black sedimentary singular rock, which appears to have a sort of brecciated structure (3035) 3035; the lower strata were partially concretionary, or necklace form; they overlay, the yellow saliferous sandstone. =

I overlooked the importance of the question at the time, but this rock contained numerous obscure fragments of shells, one of which resembled an Ammonite, & others manifestly was part of largest concentric ribbed Bivalve; Luckily the by chance specimens (3035) has a bit of Univalve?

679 verso

(a) These here perhaps contain more calcareous matter than at Copiapò?

680

1835 (4) Iquique

could these shells exist in water from which salt was precipitated, or were the fragments of shells brought by currents?

There was another stratum of dark brown rock (which at time. I thought volcanic!) with conch: fracture calcareous base with specks of quartz? 3036. =

Another section a well-defined conformable bed (of Lava) of feldspar & specks of Hornblende 3043, beneath which there was mass of thinly laminated greenish aluminous. stone marked with dendritic mang. 3042 & full of small earthy gypseous veins. — This is precisely like what has been found in all parts of N. of Chili. — Beneath this there appears to be a mass of very thin alternations of bright red ferruginous sandstone or salt. =

I found a compact. also thinly laminated black. calcareous clay. slate 3025 (like in Chili) associated with some yellow & bright red ferruginous sandstone, with few thin layers of salt. =

In different parts, I saw one (3026) greenstone. — + laminated calcareous. sandstone rocks (a) 3023 3024 (I believe above ferruginous saliferous ones) which I believe abound, but are hard to see on account of easy degradation) — Also, white cryst. siliceo-calcareous stone (3022) Also 3021 a very great deal. of a greenish, highly sonorous, compact, brittle hard .conch. fracture. calcareous. Porcelain or Jaspery rock: it is laminated, as seen by weathering, into different degrees of hardness. — This rock precisely resembles one specimen found at Hornitos near Illapel. —

As far as I am able to judge, i feel little doubt, that these strata correspond. to those already alluded to in North of Chili. — Although the Gypsum here is scarcely at all developed. I hear of it in great quantities

680 verso

(a) In which an opening of poor silver mine had been attempted. —

681

1835 Iquique

in the Cordilleras. — perhaps it is here replaced by the salt. — Perhaps through the means of these sections I may correct Humboldts geology of Peru, with what I have seen in Chili. —

With respect to the alluvial covering which conceals so effectually for the whole distance the structure of the country, the chief part consists of hard (so as to require hammer to break it) white opake, compact salt in nodules & blended with red sandstones, the grains being cemented by salt. 3050 3051 — This forms a thick crust on the mountain sides & over greater part of country; from degradation is hollow in many places & sounds under mules hoofs, — leaves funnel-shaped cavities — This crust appears in many places many yards thick. — The quantity is enormous. — Such a substance could only remain in a country where a very slight shower only falls once in many years. (a) — Yet as proved in Annales des Mines (translated by De la Beche)1 is not so rapid at Cordonza in Spain, as would at first be expected.1 — I think the chief part of this salt is owing to infiltration from the saliferous strata, during many ages & slow deposition, amongst the sand, which is either red, purple or whitish according to the hill on which it lies. (b) — We must not be surprised at the compactness of the salt, for at Copiapo (at Pasto largo) a little brook, with a small fall, encrust by its spring, during 24 hours any twig with an equal & as hard covering of pure salt, & which is collected for consumption. —

1 De la Beche 1824.

681 verso

(a) The small quantity of rain & consequent alluvial action is shown by the gullies on steep sea. coasts being filled up with friable detritus. Also there would appear be be like in one part I saw the lines of extensions water drainage is choked up and in a more shallow depression: I think perhaps the fact of loose sand being piled up against the mountains to the height of about 1000 ft (both here & Copiapo) may also be explained from same deficiency of rain (ie that in every dry country sand is blown up, but in the season of heavy rains is again removed. — )

(b) Tin label (1231) is specimen of salt from a stream Pasto largo. North of Copiapò. — any twig, plant &c. placed for 24 hours near a spot, where there is a slight fall, coats in the manner seen the object (by its spring). — Salt used for consumption. —

682

1835 (6) Iquique

That all the salt is thus produced. I am not sure, for there is a mass of sedimentary deposits, which are of same thickness & are horizontally stratified. — These consist of calcareous tufa & others which appear gypseous (3049). — But the greater part is a white friable substance, called by the inhabitants Tisa (3047). This is more or less pure, & frequently contains numerous large angular pieces of hard rocks. 3048. especially where such strata mantle round hillocks of such substances. — This Tisa is very remarkable by containing very numerous concretions of a hard siliceous porcelain substance, 3045 3046 where brown brecciated substance is traversed by rains & patches of a white stone. These concretions vary in size from size of egg to mans hand & are not of very regular shape; abound to such extent in some places that whole strata or crust is nearly composed of them; the external surface is deeply furrowed by angular ridges, a which frequently diverge from a centre, on one of the surfaces, as may be seen (3046).This seems the junction with the Pulverulent substance.

Again patches of earth are always damage & from taste contain some saline substance (3052) Mun. of Lime? : Also from Pisagua & Cuestas of Mexillones, I have some given me crystallized substance taken from a layer & probably belonging to same class of substances. —

And lastly much of the salt & sandstone is intimately connected with the beds, where the curious porcelain nodules are found. — These deposits covered partially fill up all the valleys, & are clearly a lacustrine or marine deposit. I incline to the latter, for

682 verso

(a) & appear like Pectens or other organic impressions

683

1835 6 (7) Iquique

the strata extend over the very edge of the great sea-escarpement. — & to a greater width that the

The famous mines of Nitrate of Soda, of which the expense in one year has had a value 5000 500 thousand dollars, are were seated pm the margin of a level plains. It is a [illeg] level Basin which resembles those of Chili, on those arms of the sea in W Patagonia, it is several some leagues broard (c) & extends about 40 miles to the North & is said to join to the South the deserts of the Atacama. —

From a well 36 yards deep is composed of sand & earth & a few small pebbles. — Has an altitude 3303 [illeg] is separated from the sea by the hills covered with salt &c already described. Hence if there was any drainage in this climate, the streams would flow both from E & W into this deposit basin. — The vege In several parts of this plain large trees are found buried from 1 to 2 yards deep in the earth; they are of the same sort. a prickly Acacia or Mimosa, which now grows in parts of the country; by the accounts according opinions of several people (a), these trees have been overwhelmed by floods bringing down mud from the Andes. — Both the wood & brushes are partially hardened & petrified 3044. —

(Perhaps when the upper layers were deposited from brown lake of water these were carried down?) (b) —

The Nitrate Soda is found in a solid bed (so as to require gunpowder to blast it (3054 (or 1227) 3054 on the West margin of this basin & from about 10-30 ft above its level. The bed is 2-3 ft thick, & greater part very pure

683 verso

(a) The people who have remarked this, have added there must have been more water in those days. —

(b) I am more inclined to this opinion from hearing of their occurrence over so great an extent

(c) Mr Belford Wilson, Consul G. to Peru, has obligingly allowed me to copy the official report of the exports of Nitrate of Soda. He informs me that mines have been worked over an extent of 40. leagues. & that the plain is 420 miles long. — Mr Cunningham2 in a paper supposes the Carb of Lime, as in old mortar, is converted into a nitrate & this decomposes the muriate of soda, so giving rise to the nitrate of s. If the soil with some deliquescent salt is the Mur: of Lime, such would appear probable. —

The dry climate probably would favor such changes, as protection from the rain is necessary in for providing the artificial saltpetre. — Under this point of view I am surprised at the Carb of Soda in the encrustations is not changed. —

I am in much doubt whether to believe the Tisa as well as salt overlies the nitrate. In the mines I examined certainly it did not, but the owner inclined to the former opinion. Perhaps some alluvial salt may. but I cannot believe the Tisa encrustations does; although unquestionably found on [illeg] at a level very little above the nitrate. — If the salt contains much Sulp of Soda, probably this may be a nitrated efflorescence as at Copiapo.—

1 Belford Hinton Wilson (1804-1858), diplomat who served in the Bolivian army as aide-de-camp to General Bolivar, 1823-1830.

2 Possibly Allan Cunningham, a geologist in Australia.

684

1835 (8) Iquique

rests on a sandy soil, in which I am told traces of vegetable matter have been seen. —

Is traversed by veins on cracks with sands, & is sometimes covered with the same, only a crust of the waterworn nodules of salt & sulphurous sandstone. —

The Nitrate of soda also contains some nodules of salt. — The appearance of the Basin immediately suggests a lake or inland sea (which from analogy is full as probable).

We must suppose its waters deposited on the coast the saltpetre, & subsequently perhaps the salt, if this latter is not here a pure alluvial deposit (a) —

I hear further to the North the Nit. of Soda is found amongst the hills. Indeed I think it most probable, that the sea, in its gradual retreat after encrusting the hills, as described, before finally leaving the dry basin, deposited the crust bed of Nit of Soda. —

From the regular manner the deposit, follows the Basin, it is almost certain it has been deposited from the water, which was formerly contained in it. — This would appear a different case from those saline deposits, (such as that of Copiapò of Carb & Sulp of soda) which now encrust in a friable state the lower parts of the valleys or plains of Chili & Patagonia.—

684 verso [not microfilmed]

(a) I incline to think the salt which overlies the Nit. of Soda is a I

Together with the salt, there is some Tisa (& its nodules not far distant) which overlies the Nit: of Soda. — I did not actually see this superposition but was assured of the fact by the owner, in other spots. If so it is highly probable that the same mark whole of these saliferous depositions belong to one class of facts or order of events. — With respect to the Muriate of Soda, the facility with which it could be reformed on by alluvial action of the present day renders its presence or absence of life more difficult to be understood & of less value as a proof.


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