RECORD: Darwin, C. R. Geological diary: Valparaiso to Coquimbo. (5.1835) CUL-DAR36.550-573 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrected and edited by John van Wyhe, corrections by Gordon Chancellor 11.2011. RN2

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. See the Beagle diary pp. 560-569.

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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.


550

1835 (May) Valparaiso to Coquimbo (to p. 90) (67)

I travelled from Valparaiso to Coquimbo, thence to Guasco & Copiapò. I resume the account of my geological observations from the North side of the Cerro of Chili = Cauquenes. —

From this point, for a considerable extent of coast to beyond Longotomo all the rocks are granitic, they occur chiefly in a very decomposed state, amongst which syenite & some very quartzose granites can be discovered. —

Leaving then these rocks we ascend on to green semi-crystalline feldspathic stones; which in some cases are even porphyritic with feldspar. — These I believe are altered slates. We then come to true blue clay slate. — Beyond Guachero, on the Beach such is seen to alternate with a compact, fine grained sandstone, a compact purple slate & a pale coloured rotten stone: all these layers dip to E by N W by S ∠40°. — these laminae are likewise crossed by other set of cleavage dipping north. — These rocks are crossed, numerous (poorly) auriferous quartz veins. —

From this to Quilimari there is an irregular platform of altered slate which is studded over by numerous little peaks. —

This occurs to a most remarkable extent, giving the country a singularly rough aspect. — The points are steep little small irregular cones or hummocks are separated by level little basins or coves. — I think I have read of similar forms in granitic countries; Here

550 verso

(a) Specimen from the Beagle from Papudo showed me a brown siliceous granite.

551

1835 Valparaiso — Coquimbo 68

(& further on between Quilimari & Conchalee, where the formation is similar) the points all consist of the harder varieties of the altered slate. The commonest kinds is a kind of greywacke quartz fragments, where the fragments (some of them large) blend into each; the base is now green & feldspathic — specimen shows this, contains small pieces of quartz. 2762 [illeg] Or the base is very compact red, jaspery, containing minute particles blending together & perhaps porhyritic with felspar 2862. Other paps consisted of imperfect greenstones 2860 or feldspathic rocks sometimes well porphyritic with glassy & common felspar. 2861 — Again we have a conch.fract. dark purple jaspery rock, containing iron pyrites in threads. 2863. — Or lastly very quartzose rock. — The intermediate kinds only varied from the above in being less hard & crystalline & more frequently common blue clay slate, some of which was glossy & others siliceous. — In all parts, excepting in the hummocks an East dip is clearly discernable, & even in some parts of these, such can be just distinguished. — I saw one or two N & S. greenstone dykes.

It will be afterwards shown, that shells the whole of this line of coast has been elevated at a recent period. At the present day, there are a just vast number of rocks. breakers & little abrupt Islands. around which the

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552

1835 Valparaiso — Coquimbo 69

sea is constantly moving; taking into account the altered & harder nature of the rock of the hummocks, it is in nearly certain, such have been points of upheaval, which the sea at a former period rounded, leaving & at the quite level land same time left in the intervening spaces a level & even bottom. — If the Pacifick was lowered a hundred yards, I believe we should see the very same form of land, which now extends above the its beach. — And in the course of time it is probable such will take place. —

At a point close South of Conchalee, we again meet (a) with the granitic formation here consisting of dykes & distinct mass of three kinds of granites: all the junctions bespeak violence: — the most abundant variety is a decomposing syenite containing either chlorite, mica or hornblende, or all three together, 2d a compact white quartzose granite. 3d black almost hornblendic rock. traversed by numerous white granite veins. —

These three appear to underlie altered slates or green porphyritic greenstone. The next point to the North we have the feldspathic rocks passing with the East dip into greenstones & on Isla Verde there is true blackish green greenstone 2763.

Hence the granite is included in the formation of altered slates, & without doubt has been the metamorphic & the cause of upheaval in points. —

552 verso

(a) It is highly probable that in the coast, or lowest line of section the granite might be visible in other places. —

553

1835 Valparaiso — Coquimbo 70

we must bear in mind the identity of this formation with the green feldspathic stones (& even the purple porph: breccia) brecciated grey rocks) with the of the lower parts of Cordilleras & Bell mountain.

At Conchalee I left the neighbourhead of the coast (believing I understand its geology) & turned up NE to Illapel in the interior. — In all the ravines we met with various granites & syenites; of the former some were beautifully characterized rocks.

The Cuesta de las Vacas is a lofty range. running about ENE & WSW over which the road passes; in its lower parts the stone rock is composed of quartz & feldspar, see Meyer Rose, higher up there is much of those harsh quartzose & euritic varieties, precisely like in the same class of mountains. the Prado & Zapata. — On the N Eastern side slope there are many dykes of a blackish green, close grained trap. —

Mines At Some copper mines are worked in this range; & a mines [assured] the famous gold mine of Las Vacas occur in a true granite. — In the neighbourhead there appear to be other ENE & WSW ranges & some also N & S. — At the foot there is a little porphyry of that kind, when crystals of feldspar are in form [sketch] such as 2757. In want of better name, I shall call this ([illeg]) [illeg].

553 verso

"Plate Porhyry"

(a)

554

1835 Valparaiso — Coquimbo 71

Illapel

To the NE of chain we meet with true syenite containing quartz & some of those white porphyries, which are associated with the syenitic greenstone in the Cordilleras. (a)

The hills close NW of Illapel are composed of granite or syenite accordingly as mica preponderates over hornblende. — Feldspar white often times in state of powder. — varys from close to coarse grained. — there is however much more of the syenitic greenstone, without quartz. 2864 —

Dykes of close grained dark colored greenstone. — For several miles around this town, such appears to be the constitution of the country: the whole is highly metalliferous; chiefly with copper veins. — [illeg] I examined one old mine: several broard parallel veins running N by W & S by E. — The one accompanied by vast quantities a a black micaceous iron one 2865: called by the native Liga & used as a flux. — The syenite in close contact to veins differed suddenly in degree of fineness. —

Mines [2 words illeg]

Illapel to Los Hornos

Illapel to Los Hornos — passed over syenitic greenstones, & a considerable quantity of true granite. — Several copper mines on both sides of the Road.
Veins

At last we came to crystalline stratified greenish rocks, over which were purple porphyries. — ascending a while we

554 verso

(a) For description of syenitic greenstone. V. passage of Portillo in Cordilleras. —

555A

[water coloured sketch]

(N) W (E)
Cuesta los Hornos
B Mines
N.B. Purple without lines signifies both porhyry & syenitic greenstone
NE by N
?
Porph: Breccia
Siliceous strata with petrified wood
gypsum
Road
High Hills
Porph: breccia

555A verso

P. 72.

555

1835 Valparaiso — Coquimbo 72

found the true & coarse porphyritic breccia. —

These strata (a) are together of great thickness: they dip at small angle to NE; We crossed them obliquely, the country being formed of rough broken hills, instead of the undulating forms outlines of the granites.

Having crossed the formation we came to an open even space with small water worn hillocks of gypsum strata. — Again above these we have other formation V. Plan all dipping NE towards a lofty range of porphyry & porph: breccia. — It will be seen in the Plan, in the NW corner there are several hills of injected rock. it is in these & in the intervening strata, where the numerous mines of Los Hornos are situated. — I examined the junction of the gypseous & porph: breccia, they are decidedly conformable & dup about ∠20° to NE by N. —

The upper she part of the latter consists of thinly stratified mo compact fine grained red sandstones: in places. these are greenish. — from the loose fragments there must be strata of coarse conglomerates, these rest, exactly in same manner as at Inca's bridge on crystalline sandstones & to the West we have seen the true porph. breccia underlying them. —

555 verso

(a) Here was a thick stratum of the soft white brecciated rock similarly to that in valley of Maypo. (2598). —

We may observe here, that from the great thickness of this formation, which dips immediately from the granite that the removal of similar strata on the opposite & corresponding side must have been very great.

556

1835 Valparaiso — Coquimbo 73

The gypseous formation essentially consists of a great thickness of thinly stratified pale-coloured aluminous substance: which passes in every shade from a very soft cream-coloured angillaceous calc. substance 2866; into slightly indurated greenish substance 2867, laminated laminae not thin, which is the most abundant kind; till we we have a rock almost of the character of calc. clay slate. 2868 —

With these stone there are in parts more or less abundant thin laminae of transparent or opake gypsum. — The thickest which are mined may be two or three inches but very frequent. — These aluminous stones, from weathering occurs generally in a decomposed state, in the form of a light friable porous earthy substance blended with gypseous matter. — With the above I saw a little of a black very hard siliceous stones with splintery fracture like (2870): also some compact greenish sandy aluminous stone like (2874) & a little calcareous tufa. —

There were saline efflorescences on the surface & all the water very badly tasted. — To the South, this formation can be seen rising between & forming part of some lofty hills. — to the NW it is contracted between hills of porphyry. — I picked up several fragments of what appear to a quartz vein, with copper over gypsum 2883 & the aluminous substance, which is here more inducted than usual. — I found one small hummock of a green porphyry. with white feldspar, round which the strata

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557

1835 Valparaiso — Coquimbo 74

are curiously contorted: Here the transparent laminae of gypsum are all compact fine grained, as in Cordilleras. Is this owing to heat? or a mere chance. — There is a white feldspathic dyke on each side of which there is a small anticlinal dip. — The formation as seen to in the southern mountains is of immense thickness: contains in all parts sul. & carb. of lime & aluminous matter. — I can feel no doubt they it corresponds to that which forms the highest part of the Cordilleras near St Jago. —

On the NE boundary of this formation, we have another grand mass of beds dipping conformably to the NE. — These I chiefly examined in the NE corner, where no doubt they are more altered, than in other parts. — In this formation the commonest kind is still the indurated laminated aluminous stone; this however alternates with other rocks in large quantities. 1st amongst which is a very hard, uneven splintery fracture calc: siliceo stone 2870 — There are other softer, more calcareous threads of brown calc spar, & with even fracture. 2871 2872

This rock in places contains small patches of a substance like imperfect pitchstone, but the specimen is a poor one. 2873 — Immediately I saw this I commenced to look for silicified wood: & was eminently successful in

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558

1835 Valparaiso — Coquimbo 75

finding most extraordinary quantities. (a) — The stone is of a grey or black color & harsh 2886 ... 2889 come from all; the organic structure is so much obliterated that in in a very few places it could be recognized. — The external form & impression of short branches first called my attention. 2889 common variety —

Much appears to have been the stump & roots of large trees many feet in diameter: they now lie scattered about the surface in vast quantity.. They originally were all imbedded in the black siliceous stone. — With the above two classes of strata rocks. there is much of a varying character: consisting of a white aluminous substance, either non calc sandy fine grained greenish compact 2874; or coarser with specks of mica 2875: or with crystall particles of lime & other extraneous particles. 2877 — Again we have compact brown ferruginous. calc. alum-siliceo stone 2876, or one curious harder more siliceous 2878; in the former of which distinct particles of quartz are often visible. —

I met with one stratum of calc. alum stone or tosca rock. 2879 — Some of the first aluminous slaty kinds (2885) 2885 pass into greenish porcelain rocks, containing lines of calcareous matters. 2869 — All these classes of substances are thinly stratified & repeatedly alternate, in all parts there are veins of cryst. carb of lime; threads & nodules of agate. & quartz Possibly there is a lava

558 verso

(a) Contain much ferruginous matter — From Pyrites

559

1835 Valparaiso — Coquimbo 76

interstratified 2880 for the feldspathic greenstone is described in my note book as conformable; it might however have been injected. — All the formation, taken generally, has the same NE dip as those below.

As far as the landscape is concerned they would appear to dip beneath the great irregular line of porph of syenitic & porph. breccia. hills which extend parallel across the NE. part of this basin & are called Cuesta de los Hornos. —

Examining however closely I found ore of one two points, where a fringe of strata intervened with a SW dip. — In the NW corner, these latter & the gypseous strata are broken up by numerous conical hills & dykes of porphyries crystalline rocks. — The stratification in the creeks which separate these hills is of course much contorted & irregular. From their greater softness they have suffered much degradation, at present only remaining as fringes. — The hillocks chiefly consist of white feldspathic rock 2881, which either passes into a greenstone or more commonly & in the larger hills into the true syenitic greenstone 2882 pinkish feldspar (containing dark angular fragments & epidote fracture granitic &c &c).

The main band of hills Cuesta de los Hornos. which will presently be described are is constituted in a similar manner, but is capped on the NE side of the porph: breccia; besides

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560

1835 Valparaiso — Coquimbo 77

these white or greenish feldspathic rocks, there are hills & masses irregularly underlying the sedimentary strata of a purple claystone porphyry (like those of porph: breccia formation) also others with a compact green base containing much epidote white & red crystals of feldspar. — This rock has a brecciated structure, precisely similar to some lavas, the interstices were filled up with white cryst. carb of lime. — I do not believe this substance has actually. flowed but perhaps was near the surface of a subaqueous crater. — In the principal hill (B), the lower part is a white feldspathic or syenitic rock, but the top & East side consists of a purple or greenish highly porphyritic breccia, the various lines & degrees of coarseness in the layers of fragments proves it has been a stratified rock. — This piece must then have been bodily forced upwards through the whole of the underlying gypseous (& its superior) formation. The same thing has happened in the line of the Cuesta de los Hornos. — It appears to me almost certain that the masses of injected purple porphyries, owe their presence to in a like manner to the fused inferior strata of porph: breccia

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561

1835 Valparaiso — Coquimbo 78

In the whole of this little Basin of disturbance both the paps of cryst make & their fingers of stratified rocks are threaded with metallic veins. — I believe the latter, basin Uspallata range, are rather the most productive. (a) — The ores are those of gold: vein quartzose with red oxide of Iron (like those of Uspallata) 2884 & more commonly copper, pyrites which is accompanied by vast quantities of the black micaceous iron ore, the substance penetrate & coats all the most minute, lateral crevices:

I noticed that where any of the white soft aluminous stones came near a vein, they were crossed by numerous ferruginous threads & white substance blackened & hardened, as at Uspallata. — The best veins run from between points (N & NW) (S. SE.). — they are parallel, one pap was traversed by many irregularly parallel chambers, resembling a ledge bank full of Rabbit holes. — The similarity of matrix, accompanying minerals & direction of veins (& distance not very great) one is tempted to believe the veins (& hence all the syenite) of Illapel are nearly of the same epoch of formation & which clearly is posterior to not only to the deposition but to elevation of those strata which overlie the gypsum. — On the first inspection

561 verso

(a) The inlet of stratified rocks, which to the N. in line of road winds amongst the syenitic greenstone is preeminently drilled with mines, it rises to a considerable height in the Cuesta: de los Hornos & I saw a patch of strata dip inclined at ∠ of 60°

NB. All the paps of cryst rocks are not introduced in the Plan. — Some of these appear to follow a NNW & SSE direction

562

1835 Valparaiso — Coquimbo 79

of the formation which overlies the gypseous one, a certain air of resemblance with that of Uspallata facility struck me, but to a degree perhaps. which my specimens will not bear out. — All those beds with a white aluminous cement, & those semi-porcellanic greenish stones, the black stone with pitchstone the metallic veins. underlying igneous rock. all are in evident support of this view. — Yet I am aware there is a considerable general difference.

Here moreover the strata not only conformably overlie the aluminous gypsum, but pass into it. — The general distinctness of the two formations being chiefly owing to more silex in the constitution & a more mechanical action in that structure of the former. — It is probable all the strata, before being hardened by the action heat were of a very incoherent nature. — Is their absence to the South to be accounted for by degradation? — Has all the silicified wood buried in alluvium in Chili ever belonged to such a formation, which not having been baked was not preserved? —

From the quantity of wood here & black color of S. Rocks, Land probably was at no great distance. — Were the central ridge composed of gypseous formations, as in Chili St Jago elevated into dry land. — if so this upheaval

562 verso

(a) The absence however of pebbles shows that the land probably was not very close. —

563

1835 Valparaiso — Coquimbo 80

(& injection) has been posterior to the central lines; a fact, for which I am glad to seize on the weakest presumptive evidence. — I have to notice, that the grand NE dip of the whole district appears owing to the granitic mountains which extend from the West margin of porph: breccia to the sea. — The upheaval of the higher line of the Cuesta de los Hornos & the crystalline paps probably was posterior, & anyhow has not of manifestly hard acted on so extended a surface. — We may imagine the nucleus in one case is a swelling archway & in the other an abrupt ridge. —

C. los Hornos

At the point where the road crosses the C. de los Hornos de line of white porphyry & syenitic greenstone runs about E & W. Descending obliquely the range is seen to be of some breadth, contains a good deal of white quartzose rocks 2890. with specks of hornblende mineral. — We see occasional patches of porph. breccia. both in the summit & sides dipping to the NE. — At the base of the hill to the North, this appears gradually to change till we have an E. dip; the line of hills. appearing to bend in a corresponding manner. —

Hence the line is tortuous, first N & S then E & SE. ([sketch])

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564

1835 Valparaiso — Coquimbo 81

Our direction was now a little to the East of North, to Combarbala. — We passed through the whole width of the porph. breccia. obliquely, it dipping towards the Cordilleras. — Near the above town the hills are thinly stratified & very red — much of the rock ja red sandstone & jasper, with veins & masses of cryst. carb of lime, also some of agate.

South of the town the strata all dip South, owing probably to the syenitic greenstone, a small pap of which appears. — The lower beds are red, very compact, conch. fract. sonorous. jaspery rock, which frequently has a small brecciated structure 2891, above this comes a purple Basis containing irregular opake cryst of feldspar. — This rock possessed a conglomerate structure to a very remarkable degree (a), yet I believe it is of a pseudo or concretionary nature. — Above this again there is a considerable mass of white opake, sometime curious, cherty rock; this is in places is interstratified with red sandstone.

The above rocks occur high up in the series of porph. breccia, differ slightly from the generality of that formation. —

564 verso

(a) This specimen must be examined. in my note book I refer to this, or if I considered the included specks. as carb. of lime, & of the same nature as certain nodules, the separation of which latter appears to have given rise to the sometime breccia or in sometime conglomerate apparent structure. —

565

1835 Valparaiso — Coquimbo 82

If the gypseous formation ever existed here, it must have been on the site of the valley of Combarbala. (a) — On the East side of this valley there are the main Cordilleras. — I could distinguish two grand escarpements of red stratified rocks, dipping East. — Also from the color, apparently upheaved, by syenitic greenstone.

By inspection of the imaginary E & W section, it will be seen there are four principal lines of upheaval & that all show their basset edges to seaward. —

From Combarbala to Punitaque. travelled obliquely towar seaward from the Cordilleras. — so that we agai recrossed the porph. breccia & entered on the granitic. — In the former there were several distinct hills of the "plate porphyry": also of feldspathic greenstones & dykes; the stratification irregular; some doom shaped points. —

At Paral in this formation put in, there are silver mines. the matrix of vein resembles that of S. Pedro de Nolasco. being quartz & decomposing feldspar. 2893

Near to the junction of the granitic rocks, a little to the East of Quillay, there are some poor copper mines. — The syenitic greenstone is

565 verso

(a) Probably some volcanic formation in the neighbourhead found pebbles of red cellular rock & a black Basaltic ore. —

566

1835 Valparaiso — Coquimbo 83

partakes much of the character of feldspathic porphyry, oftentimes a dusky green. — But when further within we meet true syenites with quartz & in places much black mica. — all these however are associated with the syenitic greenstones. — Such is mineralogical constitution of a steep & great Cuesta of Los Hornos.

This has the same name (& constitution) as that with one, which was crossed to the South. It appears to run NE & SW. — Very likely it is a continuation of the same range, the direction of which we showed to be very irregular. —

On the NW slope there were some quartzose paps & veins (it would appear as if in these syenite greenstones in some cases all the quartz was collected in certain spots) also dykes of dark colored greenstone.

At the base of hill on the South side of valley there are large circumscribed spaces of the syenite, & highly metalliferous drilled with mines of copper one. — other spaces solely consisted of grains of quartz & a decomposing feldspar. — The copper one is accompanied much black micaceous iron ore. — there are ferruginous gold veins. — The principal direction is NNW & SSE. —

The mineral is best known by a great number of poor mercury veins. —

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567

1835 Valparaiso — Coquimbo 84

These all occur on the opposite side of the valley where there are very few copper veins. — The mines have never been properly worked & could only see the entrances of two. — The surrounding rock is a white doom decomposing feldspar, few grains of quartz, scales of calcareous mica & traces of hornblende: the veins appear chiefly quartz (with other minerals) 2894 2895 which contain the cinnabar also mostly in drusy small cavities.

The veins appear to have same direction with the copper, are said to be very numerous. —

The granitic rocks are here backed (possibly capped) by a peculiar black green porph. with elongated cryst of blackish feldspar. 2896 — It is said mercury ores are found also in this. —

Beyond Punitaque the road to Ovalle (or Tuqùi) turns up northward & skirts by a level plain of shingle at the foot of rounded hills. — I believed I could see the granitic formation extending far to the West on the coast: I doubt whether any of the grand porph. breccia gypseous &c formations are there to be found, as in the section to the South. — Leaving then the syenites, we have on our right hand (or East) a large formation of porphyry. consisting forming

567 verso

(a) These specimens were picked up in the mouth of the mine & are of course very poor. — The miners say that exposure to the sun very soon spoils the cinnabar. —

Is the mineral from Los Hornos really micaceous iron ore. — NB. plumbago has been formed artificially in furnaces

In the Cordilleras dikes have not usually affected strata

On connexion of porphyries and granite p 114 Daubuisson vol. II1

R.N. p. 7 dikes containing chlorite2

RN dikes & faults } p. 37

NB Look to first page of Recaputulation

Subaqueous Bombs R.N. p 74

1 Aubuisson de Voisins 1819.

2 Red notebook, p. 33, ff.

568

1835 Valparaiso — Coquimbo 85

rounded hills, without stratification or brecciated structure. — These porphyries consist of the black kinds just described, which are intimately associated with the common dark green "Plate porph". — one variety consisted of large white opake cryst of feldspar, with just sufficient basis to unite them. — Amongst these rocks there was one ridge of the syenitic greenstone. Near Punitaque there were a few poor copper veins in the porphyry. —

Ovalle to the mine of Panuscillo direction still about North; all the hills various porphyries. — The mines are seated in a narrow ridge composed of very remarkable rocks. — The principal variety is a granular mixture of carb of lime & grains of quartz sometimes with specks of iron 2897 2898: more or less coarsely crystallized:

These rarely are associated with blueish slaty siliceous stone. 2900 — very commonly with a pure white granular calcareous ? rock. 2903 — Lower Low down the ridge there was some compact hard green feldspathic stone 2901 & a coarser granular mixture 2902, where the quartz? is yellowish. —

But the most remarkable & a very abundant variety 2905 is where the granular calcareo-siliceo kinds contain angular

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569

1835 Valparaiso — Coquimbo 86

patches of a more siliceous harder, compact stone. — Some of these patches are large & the outline rounded, generally small, contain minute quantity of line in interstices. 2904 — On a fresh fracture of a fragment, these patches can be scarcely discerned, but by the effect of weathering (a), become known & project far outwards giving a rough & singular appearance to the rock. From a fissured structure in these patches I do not believe they are from any foreign origin, but contemporaneous & concretionary. — Some of these patches however are porphyritic with crystals of glassy feldspar. — The patches, as seen by weathering, are arranged in obscure waving lines, which are generally parallel to the nearly vertical plans of divisions NNW & SSE (whether stratification or cleavage I do not know) which are common to all the above rocks. —

There are several copper veins in these singular this ridge; the ore is abundant, but not very rich pyrites: as in very many cases, the upper parts of the mine produced carbonate & oxides, the which gradually pass into the sulphurets

569 verso

(a) The rock which is most like this is a variety of the (metamorphic) quartz with a pseudo-brecciated structure in the Falklands. As far as structure alone is considered, the soft white brecciated substance of Chiloe might be adduced. —

570

1835 Valparaiso — Coquimbo 87

the one is accompanied by large crystals of carb of lime, & near the sides of the veins by very large crystals of greenish mica. — The best veins run NNW & SSE, but others transverse to them. —

[sketch] A SSE B C mines D NNW

The ridge is traversed by or rather partly composed by rounded hills of crystalline rocks; The Southern one (A) is high, is composed of a compact sonorous green porphyry; from this a spur is sent off & bends upwards: To the North is another hill (D) of a blackish porphyry. round the Eastern base of which the above strata fold. — in the middle & beneath them there is a mass (C) of a fine grained greenstone.

When I had only examined so far, I was completely puzzled concerning the geological nature of the granular rocks. — In the lower parts to the North of the ridge I found granites & syenitic greenstones with black mica: crossing these rocks at right angles to line of ridge. in & the direction of the strike, I found pale pink white foliated feldspar with specks of Hornblende 2906, with a well developed laminated structure, resting on the granitic

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571

1835 Valparaiso — Coquimbo 88

the laminae dipping SW 60°. — This was conformably succeeded by true gneiss; the mica however in most minute scales. — We then had have a more or less coarse granular siliceous rock 2907 2908, with most minute specks of hornblende & mica in obscure lines. —

Considering the nature of this last kind & the stratification, there can be little doubt, but what the granular limestones overlie conformably & form part of this gneiss or mica slate formation.

I call it gneiss formation, but the whole is distinct from anything I have seen in S. America. — I can form no guess respecting its age. —

To the South of the porphyry Hills in neighbourhead of Panuncillo of which specimen 2909 shows glassy elongated & polyedral cryst of feldspar, we have shown in the whole way to Punitaque there are porphyry hills. — I have no where seen so much of what must have been injected porphyry: This substance I believe has burst up through a granitic floor. — To the NW of Panuncillo. there are ranges of granitic & syenitic greenstone, generally with little quartz, running

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572

1835 Valparaiso — Coquimbo 89

from NNW to NW (a) & containing a few copper veins. — To the West, in the distance, I could see the Escarpement of the porph: breccia. — From Panuncillo to the Port of Coquimbo; in the whole distance nothing but crystalline unstratified rocks. — They consist of granitic rocks & various porphyries, some few purple:

At Tambillos, there has been a deep copper mine — The ore chiefly oxides. 2910 — it lies in a soft decomposing granite, with but little quartz. The vein runs E & W, this is nearly the first instance I have seen of a large, well determined vein with such a direction. — The neighbouring hills all consist of porphyries, some of the "Plate kind: others consisting of pure, irregularly crystallized feldspar — which by assuming hornblende passes into greenstone & syenitic greenstone. — At a projecting point. called La Punta we have the "Plate porphyry". further on we have greenish porphyrys consisting of foliated & glassy feldspar, with much pale green crystals of hornblende. —

572 verso

(a) To the SW there are some very rich copper minerales. from the outline of the hills & general geological structure; they occur most probably in the lower granitic formation. —

(b) Near the mine, picked up quartzose rock with a black mineral (2911). —

573

1835 Valparaiso — Coquimbo 90

There were some green feldspathic rocks which from their structure I consider much altered slates. —

On the coast line, we have various true granites & syenites & much hornblendic rock consisting of large crystals & little white feldspar. 2931 ... 2933 — The small plain, which here separate, like arms of the sea. the different hills, consist of tertiary strata & shingle & will be subsequently described.

to p. 107

During my residence at Coquimbo, I took an excursion to the famous silver mineral of Arqueros & afterwards up the valley of Elque to the junction of the R. Claro. A distance which perhaps is 3/4th of the interval between the sea & main Cordilleras. — The road to the min is about ENE & to the North of the direct valley, into which we subsequently descended. —

First we pass between more or less conical hills, of syenitic greenstone, granite (a). — Greenish & Brown porph: greenstone & a syenitic porphyry. — The latter I so call, because the three minerals which compose syenite are here imbedded in a red euritic base, in same manner as in protogine porphyry in Andes. —

573 verso

(a) In these hills there are some old gold mines. —

& pale green feldspathic rocks containing imperfect crystals of feldspar (2976)

(B) A little way South at Tonguy & Tortarillo (not far from Lengua de Vaca.) I had specimens of white feldspar with a green chloritic mineral. — & a dark syenitic greenstone


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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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