RECORD: Darwin, C. R. Geological diary: Coquimbo. [5-6.1835] CUL-DAR36.574-591 Transcribed by Kees Rookmaaker, edited by John van Wyhe. (Darwin Online,

REVISION HISTORY: Transcribed by Kees Rookmaaker, edited by John van Wyhe 2.2012. RN1

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Marginal notes are here integrated into the text. The section actually starts on 36.573 lower half see DAR36.573. See the Beagle Diary, pp. 569-575.

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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.


1835 Coquimbo 91

These were succeeded by a low escarpement of porph: breccia, over which the road rapidly ascended. Here then this formation is for very much closer to the line of sea coast, then we have anywhere else seen it or shall in Chili. — The intervening band of crystalline unstratified rock is here only a few miles wide. — The porph: breccia is, as before a dull red or purple color. — the conglomerate structure is in parts remarkably clear, the fragments being round, very little blended one into another, & clearly stratified.

Some others are have not a trace of mechanical origin & are more or less truly porphyritic: some of which above is a specimen 2935. with obscure green cryst. of feldspar. — There were many dykes & injected masses of the porphy: greenstone. — I met one grand dyke composed of large red cryst of feldspar & hornblende 2934 to in a red harsh basis which ran NNW & SSE. — Near to this was a silver mine. —

The stratification in in all the first part of the Escarpement is remarkable by being nearly horizontal: we afterwards have the strata bending up to SSE. —

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1835 Coquimbo 92

Having ascended over the above rock, at a considerable elevation we meet come to the Mineral of Arqueros. — The mines are scattered over an undulating district of some extent. —

Those of S. Rosa occur in the best characterized, although not richest vein. — The rocks are stratified & of a very peculiar character; somewhat resembling the crystalline sandstones in the upper parts of Puente del Inca section. — The most abundant is of a green color, owing to such coloured matter containing small white cryst. specks of Carb. of Lime & red cryst of oxide of iron (?) 2937 2938. — These rest on & alternate with a fine grained, but not very compact sedimentary rock with particles & balls of Carb of Line. 2936 — The junction of these is either distinct or sometimes passes from the nature & color of one into another. 2939

The green rock has, in one case, nea to the distance of a yard from the side of the argentiferous vein 2940 been had its particles cemented by native or the Horn silver. — The variety is exceedingly

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1835 Coquimbo 93

beautiful, & the circumstances considered rare. — The red stone frequently assumes a brecciated structure & I at the time thought that both kinds passed into rocks porphyritic with feldspar. — About a mile to the South is a hill called Cerro blanco (a) it consists of a harsh cream coloured base, porph with flesh coloured cryst of feldspar. 2942 — the lower part is without stratification; but the upper part clearly so. — A white stratum (probably from this source) may be seen in the surrounding districts underlying a a red stone. —

At the Minas de Anistoea & perhaps generally in the mineral the red kinds are more abundant than the pretty green rocks. —

At this place, we have a pale purple brecciated rock, the little bits consisting of the fine red sedimentary rock 2941 mingled with little of the green mineral. — These breccias, I believe to be all Pseudo. — some peculiar process taking place, before the consolidation of the sedimentary mass. — Here, as soon as the

576 verso

(a) Near to this there is some red pale purple porphyry with much agate & nest of crystals of quartz. —


1835 Coquimbo 94

vein descends into the green strata; it looses its silver & is of no value. — the exact converse happens at S. Rosa (only two or three miles distant) & It is there believed that when the unfavourable red was passed, the green would again cause the vein to be productive. — In the metallic vein the silver must generally occur pure, or as a muriate or as an one united with arsenic antimony sulphur &c. — The matrix is almost universally sulph: of Barytes. 2943 poor — In General Pintos mine, the native silver is associated with considerable quantities of mercury 2980 — rarely with copper pyrites. —

Mr Lambert1 assures me, that in close proximity to the silver in the same vein, masses of pure copper have been found, without on at analysis a particle of silver & on the other hand, the silver is not alloyed with a grain of copper. —

The veins appeared to me to have a NW & SE direction & much inclined but Mr Lambert maintains, that perhaps with the exception of S. Rosa, they these are not true veins but rather contemporaneous lens-shaped masses of Sulp. Barytes, either pure or containing silver &c. — There certainly appears much difficulty in following up any vein. — Yet I think

1 Charles Lambert (1793-1876), a Frano-British entrepreneur who made a fortune with copper and silver mining and smelting in Chile.

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1835 Coquimbo 95

the existence of so well developed a vein of a similar constitution with others as that of S. Rosa. ought to possess. much weight. —

Mr Lambert might urge the singular fact of the disseminated silver, appearing as an integral part of the rock of the wall. — Dom Maiano Rivers at Cerro Pasco. states the silver veins are is contained in masses parallel to the strata. — Here the Parallelism certainly appears to be absent. — In many parts there are dykes & masses of close grained greenstone, the former generally run NE & SW & so intersect the metallic veins. — The stratification over the whole mineral is disturbed & dips in very various direction. (a) — Through the hill mentioned as Cerro Blanco. — a sort of anticlinal lines appears to run across the country. —

It I believe an expansion of this ridge of disturbance has caused by its expansion, the present structure of the mineral. — In the valley we shall cross a regular anticlinal line of stratification. — Descending

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(a) omitted I believe a SW one is most prevalent. —


1835 Coquimbo 96

by a steep track at SW extremity of mineral we came to a pale brown aluminous limestone (with cryst of carb of lime) 2944, which in parts almost consisted of a petrified tubiformed corall. 2945 — Generally there were great numbers of Gryphaea & a large oyster, which is precisely similar to those found in the tertiary plains of Patagonia & Coquimbo. 2777: 8: 9: 2780 —

These strata are some hundred ft: thick are covered rest on the true porph. breccia. (not accurately examined) Have been penetrated by hummocks of the "plate porphyry". — are covered by a mass of thinly stratified black hard calcareous cherty clay slate. 2946 — Above this there is much red conglomerate. — All these rocks under appear to dip under those of the mineral. From this fact & their mineralogical nature I feel no doubt in attributing them to the age of those beds which immediately underlie the gypseous formation. — We gained

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1835 Coquimbo 97

the valley of Ague & turned up its course to the East. The rocks were porphyritic breccia: with the crystalline structure predominant. — The strata dipped westerly. — A short distance West of Pluclavo, we come to an anticlinal line visible on each side of the valley; to the East of it, we have an easterly dip.

V section

The Hill where this occurs is remarkable by an extraordinary fault; which is not perceptible in the external outline of the hill.

The stratum, which shows this is limestone included in the usual purplish rocks. — we see in the middle some nearly horizontal lines, & to the East of it, a gentle dip, which is succeeded for the distance of some miles by a continuous one. — At the Hacienda of [Phiclares]. I made a short detour from the valley, & again returned into it. — Crossing obliquely, rugged hills of the porph. breccia variously coloured green & purples. — There was one

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1835 Coquimbo 98

very pretty rock, consisting of pebbles of bright coloured porphyries, cemented with white cryst: carb of lime: & drusy cavities or interstices of green epidote. —

We then came to a more open district, with smooth outlines: hillocks of various whites & bright colors. —

[A section of the sheet is excised]

Above the uppermost white brown greenish decomposing porphyries we have a fine grained cryst. sandstone. On Above this there is the first great mass of a slaty kind of Hornstone: this has generally when most perfect a very compact, smooth conch fracture, of a pale brown or yellowish color, marked with dendritic manganese 2947: 48: 49, contains calcareous matter. — These are all varieties, more or less compact, fine or coarse grained: some black internally, but all decomposing into a white or singularly yellow & ogreous earth. — Much of the more laminated sorts strictly resembles those aluminous calcareous earthy pale coloured slaty rocks of the mineral of Los. Hornos. — At a short distance, there is a fine quarry of gypsum

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1835 Coquimbo 99

it must either lie in this stone or the inferior red sandstone. — The gypsum resembles that of the Cordilleras. — Above the first grand mass of [Hornstone] there is a corresponding quantity of a purple fine grained calc. sedimentary rock (or sandstone) with cryst. particles of carb: of lime. 2951 2952 —

This stone varied in its character being in parts jaspery, in others rubbly, & containing extraneous fragments. — Where the former character prevailed there was considerable quantities of a black siliceous rock, passing into pitchstone. 2953 — In the specimen it occurs in thin irregular layers in a greenish jaspery rock.

In the red sandstone, there were some white & lilac bands & a brown one of curious calcareous stone 2954; near to this the stone was irregular in outline (somewhat like petrified trees), siliceous & containing intricate veins of carb & (sulp?) of lime. 2055 — Above this came Bed (4) of Hornstone, greater part very yellow soft & decomposed (Bed 5) a concealed interval. — (Bed 6) a peculiar bright green, much stratified, with concretionary structure or rubbly, fine grained, calcareous, indurated green earth or clay. —

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1835 Coquimbo 100

In this are layers of a very hard rock of nearly same struc constitution, but showing a pseudo. brecciated structure. — Then some strata of the Red sedimentary stone, alternating with the softer yellow Hornstones, covered by a thicker mass of a less pure hardened green aluminous earth 2957: parts of which have a pseudo-brecciated structure. — remarkable in containing in its upper part several good sized well rounded pebbles of porphyry. —

(Bed 7) Several hundred feet of a moderately fine grained compact red sedimentary bed, cryst specks of carb: of lime 2950: in this there were many bands of a white jaspery rock, which on wetting, as at Combartala, showed a minute speudo-brecciated structure.

(Bed 8) Several hundred ft: of a white rubbly generally soft, sometimes obscurely crystalline base 2958, containing specks of green earth & grains of quartz (an indurated tufa) which frequently passes into a pale green compact hard aluminous stone. 2959 —

(Bed 9) 300-400 ft thick of a coarse conglomerate pebbles almost all porphyries, base arenaceous & with volcanic particles. 2960 Non calcareous color either brownish or more generally

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1835 Coquimbo 101

dull red. — Lower parts firmly cemented in the upper the pebbles can easily be extracted.

The extreme two feet are arenaceous, capped by (Bed 10) (150-200 ft), of strictly conformable of a compact slate coloured base with elongated cryst of glassy feldspar & some [sketch] thus shaped.

Unquestionably a subaqueous lava 2962: approaches & is almost identical with the "plate porphyries" in those however the feldspar is more frequently opake or white. — All the strata, in the above section are conformable to the porph. breccia & dip at ∠ from 20°-30° to the East. The section by as examined could not must have been at least 2 miles long, hence the thickness is about 6000 ft. —

I do not know what if anything overlies the porph. lava because there is beyond this point a disturbance in the stratification: the lava seems to proceed from a lofty & rugged hill at no great distance. — In many parts of this district there are paps of purple regular claystone porphyry & still more large dykes & masses of a

584 verso

sometimes containing in spots white earthy feldspar


1835 Coquimbo 102

green, finely cryst. feldspathic rock. 2961 — I hear there are also metallic veins. — I believe all the strata above the principal masses of Hornstone & red correspond to the supergypseous formation of Los Hornos. — I did not find any silicified wood; but I am told such is found in the Valley of Elque. —

The mountains above alluded to as being perhaps the source of the porph: lava in its central parts is seen to consist of the porphyritic syenitic greenstone, where however the feldspar is frequently but imperfectly foliated 2963: in its outer parts there is much porphyritic greenstone.

This hill seems part of an irregular N & S line of similar formation at the Hacienda of Gualliguaca. — This line has formed another escarpment of porph. breccia which dips at very small angle to the East. — Again we have another granitic N & S axis, where much true granite is found associated with syenitic greenstone & a blackish compact porphyry, with few crysts: of feldspar. — Beyond this the prevalent dip of the porph. breccia (more or less perfectly porphyritic)

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1835 Coquimbo 103

is NW by W, which appears to have no connection with the line just passed, but rather to a group of granitic hills on the South side of R. Charo. — The stratification in the whole of this neighbourhead is exceedingly confused. — A section of North side of valley is interesting from containing organic remains. — Here the strata are traversed by many dykes & faults, the general dip to the

[A section of the sheet is excised]

(1st or lowest Bed) purple hard sandstone. —

(2d Bed) 2 & 300 ft white hard sandstone, with particles of quartz & calcareous cement: in patches sometimes stained light purple. (a) —

contains some strata of a slaty sandstone & others of a light brown very compact aluminous limestone. 2965

In parts the white siliceous hard sandstone contains large quantities of small round pebbles of quartz 2972, as large as beans. — the people also here believe they are petrified beans. — At (3d Bed) 50-60 ft thick

586 verso

(a) I should mention all the white sandstone are brittle & clink when struck. —


1835 Coquimbo 104

of a dark perhaps semi-calcareous (vide specimens 2781 ... 2788) stone, almost composed of an infinite number of a ribbed unequally valved shell. 2977 — some impressions were twice the size of any of the specimens., 2978 — There were also a few Tenebratula 3132: some fragments of the gryphite (& I believe of the oyster) (a) & certainly an impression of an ammonite. — In this rock there were some few of the round quartz pebbles. —

(Bed 4) very compact, imperfect conch. fract; calcareo jaspery, red sedimentary rock, which passes into (Bed 5) several hundred ft thick of a red conglomerate, pebbles both rounded & angular consisting of purple, red & white porphyries: red sandstone & in lower part white quartz. — This main stratum by a change in color is divided into two. — In the lower part of this I examined a dyke 8 ft wide of a green base with cryst of feldspar. — higher up splits into two branches. — The conglomerate-sandstone 6 ft from the vein is red 2968. moderately hard & fine grained containing scales of mica & broken crystals; nearly in contact it becomes pale purple 2969, much harder & particles much more closely united. —

587 verso

(a) A specimen was given to me from the Cordilleras where a quartz vein appears to have traversed limestone with orthocenites. — (2979)

Here allude to M. Gay


1835 Coquimbo 105

In a similar manner. where a coarse pale purplish sandstone, little quartz pebbles 2970, united by calcareous matter, is in close contact, nea it becomes nearly white, very hard & blended, containing cryst: particles of carb: of lime. 2971 — In both cases to the distance of 2 or 3 inches the sandstone was stained greenish by particles from the Dyke. —

(Bed 6) above the conglomerate we have a thick mass (b), conformable, but showing little signs of stratification, composed in its lower parts of a dull red calcareo sedimentary basis, apparently semi-crystalline, with few extraneous particles 2974; this in its upper part passes into a nearly similar base 2975 porphyritic with crystals of a reddish mineral (a).

Is covered by (Bed 7) of true Plate porphyry, crystals both ([sketch]) thus shaped. — no passage in the two. —

And this again by (Bed 8) by a green porphyry, with specks of green earth & cream coloured ones of feldspar.

Respecting the nature of (Bed 6) I am in entire ignorance. I at the at one time thought it like the superior lavas: then a sedimentary rock metamorphosed. — But it may be doubted whether these whole mass of strata has undergone the action of Heat; otherwise all the conglomerate would have been

588 verso

(a) The upper part immediately beneath the porphyry possessed a large sphaerico-concretionary structure.

(b) Yet clearly discernable in one part.


1835 Coquimbo 106

in the state of that part in immediate vicinity of the green dyke. — I believe other crystalline rocks overlie (Bed 8). — I did not ascend higher, & their geo position becomes very unintelligible. V. Diagram P 103

The strata appear to dip directly towards a high hill which in its lower & central parts consists of unstratified greenstone & blackish porphyry & "Plate porphyry": near the summit, planes of division can be distinguished. — It is possible that this may be seat of Emption, in present position it would be impossible to discover if such had been the case: or a point of extreme metamorphic hear has produced the singular (Bed 6) without affecting the conglomerates in & to the South of the ravine. — I am very doubtful, in what precise part of the series this section comes. — From the nature of pebbles it is nearly certain, that some of strata, nearly similar to these, existed as dry land. —

Probably some central chain. (a) — There is a considerable resemblance

589 verso

(a) By referring to Copiapo it will be seen how little reliance can be placed on mineralogical resemblance or continuity in the strata. — Also a coarse conglomerate, is there found at very base of the series.


1835 Coquimbo 107

in the conglomerate & capping lavas to the upper part of the Pluclaro series. — I am however inclined to believe these rather come just below, or in lower part of the gypseous formations. —

We shall subsequently see the same fossils thus situated. — I have drawn a section (it is not very accurate) which will serve to make the above description of the section of the Valley of Elgue from the sea to the R. Claro more intelligible. — By comparing it with that to Combartala a general resemblance will be perceived. —

Coquimbo to Giasco ( — coast road)

On road to first stage of Yerba buena; irregular hummocks & cones of syenitic greenstones common greenstones & dark porphyries protruding through 2983 2984, crystalline greenish, ore or less granular feldspathic, which is betraying traces of cleavage I believe to be altered clay slates. — From Yerba-buena to Carizal, form of country. similar to that near Quilimesh constituted as before, pass chiefly feldspathic greenstones.

590 verso [blank]


1835 Coquimbo — to Guasco 108

At P. de Choros green & purplish brecciated compact rocks, where the angular small fragments are either more siliceous or feldspathic, but generally of same constitution. — It is a similar rock to those on the coast near Terilimani &c North of Valparaiso. — These strata are traversed by some grand N & S black hornblendic greenstone dykes. — The brecciated rock more compact, with a fracture more conchoidal in the close vicinity at Carizal granitic rocks. —

Carizal to Sauce

At P. de los Leones, granites which by a linear arrangement of their mica & hornblende in places affected the character of gneiss. —

Having passed Quebrada Onda, entered a grand mountainous mass of true fine granite.

Low down in one ravine, there was an appearance of stratification. — The lowest bed consisted of the usual kind with large plates of black mica: lying upon this with an even junction there was 18 ft of a fine grained very white quartzose granite, with very little mica.

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