RECORD: Darwin, C. R. Geological diary: Chili. [1834-1836] CUL-DAR35.377-418 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)
REVISION HISTORY: Transcribed by Kees Rookmaaker, corrections and editing by John van Wyhe 6.2011. 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. Darwin was in Chile from February to June 1835. This period is treated in the Beagle Diary on pages 553 and following.
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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.
V P x
Excepting this observation, the loss of mica in the basal granite. would seem to point out a probability of transition between
the it & the superimposed rocks. — To return to the Campana
Describing downwards: the summit is formed & a great hump-backed mass "mons" about 800 ft thick of (2272: 3) coarsely highly crystallized greenstone. V (a) (a) This rests on a thick bed of what in all its general appearance resembles an altered clay-slate. — Specimens
2267: 68 2276: 77: 78 show a pale coarse semi-feldpathic rock; occasionally conchoidal fracture sonorous when struck; close inspection in some pieces show a porphyritic structure (2268) with yellow crystals of feldspar.
The whole rock is divides with a very regular & constant cleavage, which dip at high angle to E by N: there were variations in color parallel to their layers. This bed is several hundred feet thick. it contains in its central parts a bed of
[illeg] greenstone (2279), only differing from that on the summit by being rather less brilliantly crystallized; this bed is parallel to the cleavage: it passes into the altered slate by the most gradual transition perfect transition, incontestably proving it has not been injected between its layers. — Beneath this the "altered slate" has in parts layers (parallel to cleavage) of the Trichite; the same mineral we have seen in hump-back of crown of greenstone: (؟ & in the granite veins near Valparaiso?). —
We now come to an immense mass of a fragmentary nature & red color; no hand specimen can show with distinctness the angular (& occasional rounded pebbles) breccia; because this no where remains.
(a) This greenstone contains veins & abundant masses of (2274) a green mineral (Trichite?): also on the very summit. Brownish? in a greenstone base (2275). — Perhaps there is some gold here for a small mine has been worked on the spot. — The rock is much divided by smooth planes of fracture & broken to the extraordinary degree, which is common in greenstone mountains. Respecting some curious observations in the freshness of the fracture, V. Private Journal.1
NB (1835). It must be borne in mind, that the term porph. breccia includes breccias & conglomerates of porphyries & these rocks, which have undergone subsequent alterations as to be partially blended together or that the cement has become porphyritic or that the brecciated & sedimentary structure is
destroyed completely or nearly destroyed. — Besides these legitimate varieties it is highly probable that there are streams of subaqueous lavas included, which I could not distinguish & perhaps by accident some unconformable injected porphyries. —
Pxx The upper parts of M. Wellington, a mountain 3100 ft close to Hobart town is formed very similarly with this. — The veins of greenstone are even perhaps more magnificent, but the
absence antiquity of fresh all the fractures was very clearly to be seen. —
1 This is a reference to the Beagle diary, p. 253:
17th [August 1834] We climbed up to the highest ridge of the rough mass of greenstone. The rock as is so generally the case was much shattered & broken into angular fragments. I observed, however, here one remarkable difference, that the surfaces of many enormous fragments presented every degree of freshness, from what appeared quite fresh, to the state when Lichens can adhere. I felt so forcibly that this was owing to the constant earthquakes that I was inclined to hurry from beneath every pile of the loose masses. —
evident, excepting where the fragments are large. The rock contains much feldspar crystallized; & passes into a true clay-stone porphyry. I have seen in thousand instances the most gradual transitions. — But of this hereafter. —
Specimen (2280) for a hand one shows tolerably well the breccia structure: the feldspar is here in irregular angular patches, in lines, as also in the Trichite, which it contains (seen on a large scale
) these are parallel to the cleavage of the altered slate). This pale purple compact breccia passes into one (2281) where the feldspar is better crystallized. We again have the altered slate (perhaps 2000 ft from summit) with soft porphyritic greenstone & much trichite. — Beneath this there is an immense mass of blackish purple porphyry (2282), crystals small not numerous with a little trichite; this variety passes into others such as a white one (2283) & a an abundant red compact perfect clay-stone porphyry. — In these rocks the breccia structure could occasionally be just obscurely distinguished. —
There were included masses of porphyritic greenstone. — Beneath this I could not follow any good section. — There was much porphyry. the base alone without crystals being common (such as 2265) & greenstone.
The lowest rock &c &c &c V. P. 6 & 7 X.
To return to the Campana. I will describe part of another but less satisfactory section, the result being much the same.
There was a mass of most evident breccia. The basis, red softish aluminous nature, with angular irregular sometimes pure (2265)
This generally contained many large irregular crystals of dull white feldspar (2264) &
(a) (1835) Visited Umirè, south foot of Bell of Quillota
The lowest fringe is a harsh white siliceo or feldspathic rock , generally in a decomposed state, often with quartzose veins. — Resembles the formations in the C of Prado & Zapata & unquestion[ably] belongs to the granitic order. — At half a mile distance we have a hill of true syenite — above the greenstone base there we have a greenish cyst feldspathic stone, without distinct crystals, containing green angular patches, these strata alternate with regular purple porph. breccia: above these a considerable mass of pale altered slate as on summit without any distinct crystals: parts of this have a brecciated structure, containing angular patches of black cyst & other rocks, & broken (??) crystals of feldspar, edges blended into each other. (2859) All these strata dip at high angle to the South. — Therefore this must be extremity of short N & S line of upheaval. — On the SE side of hill & high up copper mines are worked. At Caleo there are mercury veins. — We have seen gold & silver is found.
Also loadstone occur in the vicinity. — How are we to account for same granitic formation being here thickly covered with stratified rocks (Bell mountain ∠r observation 6200 ft) & the Prado & Zapata not so. — Placed
in almost in the same line, vicinity to Cordilleras & circumstances. — Has the Bell been old volcano? — Or was the Cuesto of Prado & Zapata slightly elevated, so as to prevent sediment accumulating on them.
even in hand specimen. Breccia structure can be seen; close to this there was fine sonorous 2266
porphyry greenstone porphyritic with feldspar (some acicular) & amygdaloid with quartz (?). Again we had a breccia or red greywacke, with its particles blending & uniting into a porphyry: altered slates (2267: 68) & porphyries (2270: 71).
Amongst all these every now & then a pseudo-breccia (such as at Port Desire) might be seen. — Poor gold mines have been worked in several places in the altered slate & the basins of the porphyry. — So much for the mineralogical structure. As the altered slates alternate with the breccias &
P various porphyries & as much of the greenstone is included & passes into the altered slate, the origin cause of their crystalline structure must be the same & this manifestly (from greenstone & porphyry) is fire. — From the breccia & puddingstone, we are sure they have not flowed in a melted state;
we must come to the conclusion, that
a this enormous mass of rock little less than 4000 ft high (it cannot not be known how thick, because dip is unknown) has been so much softened as to allow the particles to group themselves & crystallize. The variations in chemical nature would might determine whether one layer should would be greenstone or altered slate. — the mechanical structure probably also influenced as the creation of the porphyries. — It is very possible that some of the greenstone, (such as in 2d section, 2266 with acicular feldspar) may be parts of dykes exposed. & have really flowed. — The "Morro" or hump-back of coarse greenstone on the summit, the very form of the hill, almost shows has
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been protruded from below in a melted state. It was probably, at first covered up by beds of the baked rocks such as now lie around the lower parts; & these by time (& when this mountain was an outlying island) have been removed. — The ridge of the Campana & other neighbouring hills runs in N by W & S by E line, which is exactly parallel to the cleavage of the slate: I have said
the its dip is E by N at an high angle which is directly under the "Morro" of greenstone. It must be remembered that the laminary of slate, bed I have not seen true stratification, for instance a bed of slate overlying the breccia; for I consider, the lines of minerals in the porphyries, the laminae of slate & the beds of included greenstone, as only examples of mineralogical change, parallel to the cleavage, which I have noticed in the granitic & other rocks. —Indeed the very direction of dip shows this has little alone almost proves the distinctness of the two cases. — I imagine that the strata of slates & porphyries &c dip from the line of the Morro of greenstone elevated into this position during its possession; perhaps the cleavage was originally nearly vertical, when the dip of the strata would necessarily incline the laminae towards the mountain. I can believe the mountain to have the structure represented.
slate &c &c granite
original covering [illeg] altered strata porphyry & breccia slate porphyry granite
The first section described is supposed to be in the dotted line, which may represent the section of a ravine of west side the mountain. —
West of the city of Aconcagua, I found red & purple porphyries, mingled with a coarse & palpable breccia: spec 2285 is intermediate in its character
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There was included bed of greenstone or greenish porphyry (2286) I hardly know, which name to give it. — Some of the porphyry contained
small minute crystallized patches of white carb: of lime. — Perhaps where shells were contained before the application of heat. — The strata were nearly horizontal but little inclined, the dip being about NW. —
This was at the base of the mountains, which form West barrier to the basin of Aconcagua. — To the NE of this at the mines of Jajuel I well examined the structure of the hills the prevalent rock is the breccia = porphyry, the former character preponderating. — All the strata dip at small angle (10° & less) to West, varying however from NW to SW. The main range of the Cordilleras to a height of 6 or 7000 ft judging from color & structure are composed of the same rock (a) & have the same small western dip. —
I ascended a very lofty hill, probably 4000 ft above the level of the house & valley & 5000 above sea: I passed over an intricate mass of crystallized rocks; there was much altered slate with distinct cleavage or rather (2294) pale-colored feldspathic rock) which ran in a N by E & S by W line parallel to the ridge. — I found one bed of blackish, irregular ∠r cleavage, siliceous altered clayslate (2293). This, with the excretion of the red basis of the porphyries, is the only rock I have met with in this point of Chili without some approach to a crystalline structure & another common rock is a fine grained, grey (2295) greenstone; This & the altered slate, often assumes acicular crystals & feldspar. — There was much of the usual red. porphyry & breccia; the latter in some cases, from the rounded pebbles rather deserved the name of pudding-stone.
I noticed in a pale porph. needles of hornblende. I saw this form of the mineral no where else; I
(a) Mr P. Scrope1 seems to consider the greater part of the height of the Andes, owing to rock which have flowed; I could not ascend higher than 5000 to 6000 feet owing to snow, but I no where met in
Chili the Andes of this part rocks which have flowed: neither could I see any above me. —
(b) Mr Miers2 makes (Barom: observ) basin of Aconcagua 2500 ft above sea; if so the base of this mountain must be at least 3000 ft. its absolute elevation little less than 6000 ft. — Hence also the strata of porphy. breccia seen in the main chain must have reached to a height of about 8000 ft. —
1 Scrope 1825.
2 Meiers 1826.
altered slate dip to SW by S ∠ 12°
porph = breccia
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may also mention, that mica is not to be seen in the above described rocks. — At the very summit there was breccia & much of the red porphyry; we shall subsequently describe plenty at the base; as the dip is nowhere more than 10°; the height of the hill, perhaps more than 3000 ft) must nearly express the thickness of the beds altered by the action of heat. — At this highest point, I found mass of the red porphyry (or altered breccia) reposing with a vertical suture on a fine grained greenstone: the edges of which were stained purple, but quite distinct. I of course immediately thought that this was part of a dyke, injected in the porphyry; to my surprise within a few yards I found a tapering vein of rather more crystallized
gre porphyry penetrating the greenstone: it would appear that both rocks had been softened & by some force mutually had displaced & penetrated each other, the both originally having been without doubt horizontal beds of an uncrystallized rock. — Between this lofty hill & the main range a longitudinal narrow ravine affords some good sections of the lower hills or very base of Andes. — Pl: 1. shows a cliff from 400 to 600 ft high, the lower part is composed of a bright a breccia = conglomerate semi-porphyritic & a bright red jasper (the altered base). The strata dip to SW by S at ∠ 12° to 15°. They are penetrated by a vast number of zig zag dykes of a feldspathic greenstone (2287) porph: with feldspar; some of these are for short distances strata shaped. — One main one 15 to 20 feet broard runs obliquely across the cliff. — the drawing does not nearly represent all or the intricacy of these dykes. The breccia & greenstone are quite distinct at point of contact; the former is not altered (having the whole undergone or undergoing the action of heat), the greenstone at the very edges are stained red, from the iron of the breccia.
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Any small projection on one wall of dyke, has a corresponding depression [sketch] on the other, showing it is a rent in the rock, injected with the melted stone. — Above the breccia, there is a great mass of feldspathic greenstone, 200 to 300 ft high, it reposes conformably on the strata of breccia: the rock is scarcely to be distinguished from that of the dykes, excepting by a mere shade of color & not containing quite so many crystals of feldspar.
I had at first no doubt it had flowed through the main dyke, but upon close examination, I found the semi-porphyritic breccia & the greenstone were united (however odd it may sound) by the most gradual transition in nature & were color. — There can be no doubt the main dyke crosses this conformable mass: (I could not see it owing to nature of ground). How strange thus to see the two rocks, so alike, one which has flowed, the other been merely altered in situ! Lower down the ravine the breccia reposes on a conformable bed of well crystallized greenstone. — who after the above facts can tell its origin? — on right hand of Plate there is a mass of pale purple,
por well crystallized porphyry, where the brecciated structure is scarcely visible. — its connection with the rest of cliff of breccia is not very manifest. Perhaps it has been protruded upwards for some lower melted breccia, (as on the summit of hill described yesterday) in the same manner as the greenstone, from melted slates traverses the altered state, — also a greenstone. — On the opposite side of ravine facing the cliff, we find
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nearly the same breccia, porphyries & greenstones. In a like manner the beds are threaded by greenstone dykes. — When it is considered there are merely vertical sections, it is evident that the rock must be penetrated with dykes, like an animals
with body with the vascular system. It would seem probable, that the liquid ocean of greenstone had been at no great depth below; perhaps & that its expansion had cracked, penetrated, & upheaved the strata. I should be inclined to think that the breccia had become semi-porphyritic anteriorly by the long continuance of anterior heat.
Besides the dykes there are many
massive veins of copper; these occur in the greenstones & altered slates: not being found, oft it is said in the breccias. — I examined one in which copper pyrites & a very little gold occurred in crystallized carb of lime, which latter coated in layers the walls of dyke, as if precipitated by water. — Similarly in the hill above the cliff (Pl: 1) we have numerous veins of copper which cross each other in an intricate manner. — there are others of iron glance. — I observe the rock in the close neighbourhead generally seemed altered from its usual character. —
I could not find out, that the veins followed any particular direction. —
In this neighbourhead there was much of the semiporphyritic breccia-conglomerare. All the fragments are now converted in porphyries, of course it is impossible to know what were the original rocks: I found a few quartz pebbles; & many fragments were 4 to 6 inches across. —
(a) For a partially different view concerning the origin of the porphyritic-breccia V. First page of passage of Andes from St. Jago to Mendoza
Hence videlicet pink porph. (2291) may possibly be a lava. The curious porph (2292) I feel little doubt is an injected pap
The transition from decided breccia to true clay-stone porphyry is seen in numberless instances.
Specimen (2288) is a coarse porphyry, with grains of quartz, this latter mineral is common here, but very uncommon in other porphyries; — the breccia & even conglomerate structure is tolerably distinct. — Spec.s (2289: 90) are abundant, they well show by the green fragments, that where the brecciated structure is best seen, the porphyritic is absent & vice versâ; — (2291) pink porphyry with quartz & feldspar: —
The curious rock (with
green green fusiform balls & cross shaped plates of feldspar) (2293) p 20 Appendix almost composed one low hill. —
In a low cliff, I saw the following ascending alternations. 1st breccia, 2d jasper & the red aluminous base; 2d porph-greenstone; 3d breccia partly converted into red porphyry 4th porphy-greenstone 5th red porphyry 6th altered slate 7th fine sonorous greenstone. The alternations of the breccia & porph: greenstones are clear & distinct & there is no passage from one to the other. Yet it seems probable that the porph-greenstone is an altered rock in situ; perhaps the fine sonorous greenstone may have flowed from some dykes:
But who can say, after all the foregoing facts here & at the Campana,
whether which is the true origin. — Perhaps (I feel great doubt) the greenstone which contains acicular crystals & feldspar have flowed in dykes generally & on the other hand the greenstones porphyritic with white opake large crystals of feldspar, have been altered from in situ. A slight probability is given to the latter part of this doctrine, by observing the same sort of opake crystals of feldspar in the porphyritic breccia & again by the fact that the fragments of slate in greenstone dyke of Cockburn Channel, T. del Fuego, were porphyritic with similar crystals of feldspar.
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f 386 removed to f 410 of which it forms part. PJG 29/1/80 [archivist note, not in Darwin's handwriting]
although so blended with the surrounding greenstone that the edges could hardly be distinguished. — There is another reflection, as we see that some rock (probably a more fusible slate) which alternated with breccias, by the action of heated is converted into a greenstone, difficult to be told from that which has flowed in dykes (a), we may feel sure, that the latter is produced from the more complete fusion of sedimentary strata. —
Directing my course from Aconcagua to St Jago. — I noticed strata of the porphyry dipping to SW at angle about 40°, it was at the foot of the Cerro de Talguen. — Further on in the lower parts, there were varieties of trappean rocks (2230: 31) & higher up the old. porph=breccias. — At Porpico there is a formation of black, very compact, conchoidal fracture limestone with thin white veins (2232). The strata dipping westerly about ∠r 10°. — It seemed associated with the usual crystalline rocks. — Is said by workmen not to contain organic remains. —
St. Jago. — The little oblong pap of St Lucia, stands like an abrupt island in the great plain; it is composed. — of a very feldspathic greenstone (?) (2233) with crystals of feldspar. sonorous & conch's fracture. — The rock is primarily divided into great cylindrical pillars & these are properly subdivided into great cylindrical columns. They dip to SE ∠ 45° — obliquely to the horizon. — on the Eastern side of the hillock the columns pass into globular concretions of a coarser greenstone. — In the line of its ridge NNE 1/2 E & SSW 1/2 W there is a spur (or peninsula in the plain) branches off from the Cordilleras. — it is called the hill of St Christopher.
This is composed of precisely similar columnar feldspathic greenstone. but
in one place the columns dipped in a directly opposite direction to what they do at St Lucia & in one place towards this hill. — This renders it almost certain, that these paps have
(a) Mr P. Scrope1 considers the component crystals in lava to have existed anterior to its fusion: in these greenstones & porphyries we see that crystals of feldspar — hornblende, grain of quartz, pechinine & perhaps others minerals are actually produced by heat from the sedimentary strata. —
1 Scrope 1825.
elevated ejected distinct & have not formed originally parts of one ridge. — Connected with the feldspath porph, there is some, snuff=colored, fine grained ferruginous greenstone (2234); the basal parts of one West side of this hill, the are covered by the semi-porph. breccia (2235) as in the Campana of Quillota: & this is the key to the explanation of the origin of these paps; the greenstone has been protruded amongst overlying strata. (hence their hump-back form), which have partially or entirely as in the case of St. Lucia been removed, when the sea covered the plain of St Jago. — It is of some interest finding this little chain of points of elevation (a crack or fissure enlarged at certain points), both as an index of what may occur on a great scale & as being connected in an oblique line with (NNE 1/2 E &c) with N & S line of Andes; whereas generally these lines appear to be parallel & distinct. —
The Cordilleras, near St Jago contain much porphyritic greenstone (2238: 39); also the common purple porph:= breccia; the former of the characters quite preponderates: the strata dip in one place to WSW ∠ 15°. — the dips seem subject to much variation. I saw them high up nearly horizontal: on one
fine great hill the strata dipped directly towards it; as if the one outer half had disappeared been carried away. —
On the road to the Baths of Cauquenes saw much of the usual greenstones & porphyries. This was the last place, where I examined the western basal parts of the Andes. — Close to the
very baths in the watercourse of the Cachapual, there are beds of the porphyritic breccia. some of these are most manifestly & coarsely brecciated, others are marked, parallel to the stratification, with what I have called water lines, that is a fine arrangement of small particles according to their specific gravities
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Such strata abruptly alternate with a blackish purple rock (2243) only slightly porphyritic & where if the brecciated structure is visible ? it can only be observed by
angular patches containing a greater abundance of crystals. — The brecciated strata where is assumed a slightly globular structure, the sphaeres being placed in lines showed that this structure would easily pass into the columnar.
The rocks were crossed by a large dyke of a blackish-green fine grained greenstone (2244). — The occurrence of dykes traversing the porphyritic breccia I noticed in other places in the neighbourhead. — The above strata dipped to W by N 1/2 N ∠ 37°. — In the direction of these beds behind these (South) three baths there is a high hill, on the summit of which the
dip western dip is increased to 67°. — The greater part of this hill is composed of various breccias, their basins, porphyries (such as (2246) which are often amygdaloid & ferruginous — porphyritic & ferruginous greenstone, & the strange porphyry with cruciform plates of feldspar (?), already mention at Jajuel 2247 containing irregular nests of agate: 2253 & 2254 with carb of lime. —
The origin of this rock, I do not know, whether injected or altered in situ. — At the
base lower parts of the hill the greenstone appear more abundant, it may be from their protrusion that the increased dip is owing. —
small amygdaloid (z)
I have said, in this line (A) of hills the dip of the strata & height of land suddenly rises, parallel to this a little more
[illeg] (about a mile) to the West there is a longer line, which in a similar manner has a small dip low down in the valley of the Cachapual, but to the South
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They It continues rising, till at a distance (5 or 6 miles) they may be seen forming a lofty mountain with absolutely vertical stratification. It may be noticed that the nearest chain of the Andes appears to bend, or throw off a branch to this point of extreme disturbance: no where else have I seen in the basal skirting mountains or the Andes themselves outer chain strata dipping at a greater angle than 30 or 40 & even this is very rare.
This form of stratification must be owing to points of more forcible upheaval in a line of fissure; perhaps where the strata are vertical, melted rock has actually flowed. —
On the valley between the two above lines of hills & close to the R. Cachapual there is a small but very singular formation, it consists of
[illeg] quite horizontal bed of semi-acicular form of a cellular trachytic rock, with elongated crystals of glassy, fractured feldspar (?) (2248) (2256). The upper surface is highly cellular (2255) much more so than other parts of the rock. — Seeing the nature of this, its superior cellular surface, its horizontal position, flanked on each side by rocks of a different nature & with a considerable dip, it certainly appears probable it has flowed from a point of emption. — i could not see its actual contact with the surrounding formations: This little basin is 4 or 500 feet above the Cachapual, its edge forms a vertical horizontal cliff on the South shore, on the hill side.
It is perhaps 1/3 of mile long & scarcely so broard, on the opposite side of the valley however, there was a patch of
Are not basalt strangely rare in this country where every thing bears the marks of fire ?? —
rock, which judging from its form might belong to this formation.
The presence of this trachytic rock, is so much the more curious from it not occurring in any other locality, which I have seen & from its form, that of an ejected stream, which I have equally not met with.
One would be inclined to suppose that it burst forth during the great & unusual disturbance of the neighbouring
strata hills V a; but if we grant this, tha we must also grant that the land at that period almost took its present form. — that the great valley of the Cachapual (excepting the lower 400 feet) was then formed.
valleys ravines of the Cordilleras seem to require an almost endless age, during which the action of water removed the great masses, which must formerly have intervened between the regular & even strata on each side of the present valleys. — With base dykes at the same time can we believe that the continuation of these same ravines was formed by upheaval & has subsequently only been lowered a few hundred feet. — The difficulty may be removed by supposing these lines of striking mountains were upheaved long posterior to the formation of the greater part of the ravines of the Andes. — & that the trachytic rock (perhaps a greenstone dyke, its mineralogical nature altered from the removal of pressure & which poured forth its contents) did actually flow at this epoch & subsequently the has been cut through & the valley lowered as the land gradually rose. the origin of which consisted, as in a failure of the force of upheaval in that
(a) & that the lesser dip, already described (V diagram) at this very spot, in the valley of the Cachapual was owing to the ejection of the fluid rock have removed part by
upheaved subterraneous pressure. —
I am very unwilling to admit, the only other explanation, that the trachytic lava flowed, subsequently to the excavation of the valley by ordinary means. It appears to me the slope of the hills, in conformity with the [illeg] dip, towards the valley of the Cachapual, almost proves this part to have been so originally formed. — I at first thought, that the hot baths of Cauquenes, was connected with the disturbed strata, but as others occur higher up the valley I see no good reason to believe in this. —
I visited a high mountain in the main chain (probably 5 to 6000 ft) near to where the Cachapual divides into the ravines del Yeso & de las Cypressos. — The main part of this hill was composed of the usual porphyry, where the brecciated structure was occasionally visible.
؟ perhaps in the more central ranges this structure gradually disappears.
I saw in one place an extensive mass of (2250) compact, heavy fine-grained slate-colored greenstone with a few crystals, some acicular of feldspar. — this bed lay beneath & conformable to porph-breccia. The summit of the mountain is chiefly composed of pitchstone porphyry (2249), with a regular columnar structure: even in this rock, the brecciated structure I believe was in one spot visible. — This is of some interest, because it may account for the pitchstone at P. Desire. —
The common porphyries were brightly red, like vermilion, in many inaccessible places I see could see the mass entangled by
white dykes; white some of these which I reached to were ferruginous greenstone. — Feldspathic rocks with various crystals & others I could not understand (2251: 2252); the rock in some of
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was slightly cellular. (v. specimen) which in a dyke I believe to be very uncommon. — (a)
Near S. Fernando & on the sound there met plenty of the porph. breccia: As I here left the neighbourhood of the Andes it was the extreme southern point, where I saw it.
This formation appears to me so remarkable as to be worthy of some reflections. I mean by the term porphyritic breccia, a series from, coarse true breccia & conglomerate or finer sedimentary deposits with water lines, to true purple or red claystone porphyries. — The gradations of which I have observed in numberless & most insensible passages. — And hence I am strongly convinced all
the such porphyries in this district owe their origin to partly fused more or less coarse sedimentary dep strata, partly fused in situ. — That such porphyries might flow in a stream, is very possible, after what has been seen of the little dyke, at Jajuel, penetrating the greenstone. — & indeed at Chiloe a claystone porphyry (& much pitchstone porphyry) from parts of a stream of lava. — Hence this double origin may be considered as proved. — we have already shown a similar fact with respect to greenstone. — This porphy= brecc: is an enormous formation. I have seen it composing far the greater part of the western ranges of the Andes for a distance of 140 miles in latitude. — An intelligent person assures me he has seen it abundantly at Petorca, (where it is more plainly conglomerate) which is 30 miles more to the Northward Southward. — At Jajuel I have given reasons for supposing it at least 3000 ft thick, the Andes up to 8000 ft, or rather that beds occur at intervals to that depth. As it appears to
(a) I have not seen one vesicular or
cellular amygdaloid dyke which I can remember in any part of Chili. — It shows under what pressure the fissures have been filled up with fluid stone?
These dykes occurring in same valley, where the only lava stream is found, which I have seen in Chili is found — is probably more than accidental coincidence. — (Nov.r 1835)
There were also masses in same mountain the position of which I did not rightly understand of the same kind of cellular porphyritic stone.
ascend to much greater elevation as is found at the base & as the dip in the main ranges is small, it probably is of even much greater thickness.
With respect to breadth it is only generally found in the Andes & the ranges near to them, but the frequent dip, in this latter case, towards the Andes, shows the connection is only that of an original horizontal bed, upheaved by the parallel lines of elevation. —
We find it however on the West foot of the Campana of Quillota, with all its usual characters. — How is it we do not find it in the latitude of Valparaiso extending from the Andes to sea-ward? We cannot suppose so great a formation could be deposited in spots. May it not be only now present, where a line of
fissure upheaval has removed parts from the wear & tear of a former ocean at a higher level. — na a more natural explanation is that the lines of fissure upheaval (or concealed green igneous rocks) have altered & hardened the breccia, so as to withstand wear & tear; other reasons would incline one to suppose that this process had taken place [anterior] to elevation of strata. (no particular attention in sides of dykes: the little eminences yet existing in walls of dykes, showing rock was hard before injection. V. Jajuel;
this difficulty may be removed by supposing that the dykes, as distinguished from great hump-like masses of greenstone, were injected at a later date, subsequent to the elevation of lines of hills. — I do not quite like this hypothesis). — However this question may be settled there can be no doubt, but the greater extent of the formation ranges parallel to the Andes. — With respect to the age of the rocks, which compose the grand chain I have no data: the probability is that it is transition: for the ammonites of T del Fuego
(a) A line of hills parallel to the central axis would prevent the extension of the coarse sedimentary rocks, beneath the sea —
The Campana of Quillota might have been old volcano. —
to the South & those of Laguna to the North & the Tenebratula of Huantajara near Tarapaea, & those of (Guancavelica (?) near Lima. "Ulloa not Ammerican" would seem to point out some such age. (I hear the Cordilleras in these parts are conchiferous). — But the consideration of the nature of the porph: breccia leads one back to a far similar age.
Where could the enormous mass of angular fragments ranged parallel to the line of present mountains
have come from, but from some & which they chiefly compose, have come from? Does it not almost demonstrate, that the nucleus of the Cordilleras then existed at this remote period, (anterior to the deposition of transition beds?) as a chain of mountains, washed by a sea, where the debris were collection during a succession of ages. It is impossible to detect conjecture, what could have caused the subterranean fire (literally according to the Huttonian theory) to have broken these deposits & then elevated them by an elevation in the line of the former chain to have given them a corresponding tilt. — If this reasoning is correct, it makes the Cordilleras of the Andes nearly as old as the world is as interpreted by geology, — & this surely is no more consonant to its magnificent dimensions, then a sudden outbursting in the tertiary period. — What the nature of the mountains which composed them was, from above the breccia derived its fragments, it is impossible to tell, because the pieces themselves must have been altered, by the heat they have undergone. — indeed it is certain, they more
(a) Miers travels1 (cannot at all be trusted in geology, talks of all Chili as composed of syenite) says there is porphyry on the very [centre] & breccia a little lower: if this is same formation as the West exterior strata, it renders the existence of the anterior chain
of a puzzle; for one must suppose they had in this case it must have been so much demolished, that only if any part still existed anterior to the re-elevation it could only have been under the form of islands, but must have. Yet its presence at some period remain equally clear. — (b) It might have
(b) to reason from this supposition into remote contingencies, it has been remarked, that the anticlinal beds on opposite sides of great chains of hills are often different (I do not remember whose remark), if such a central nucleus has often existed as an anterior range of hills, it is very probable that the deposits into different seas would be different, yet when elevated in their position would correspond. —
1 Meiers 1826.
easily became porphyritic, then the red basis or cement which unites them. — If I had not seen both conglomerates & breccia & where the nature of different rocks was most manifest, (even finding quartz), & lines of water deposit parallel to strata, I should have had doubt reflecting the origin of their rocks so intimately mingled & connected with those of crystalline structure.
At the Baths of Cauquenes there was
an a curious appearance which might be brought forward as an argument for the concretionary origin of these pseudo-breccias. — partly rounded fragments had coloured internal bans, exactly following their outline; or they were traversed by angular figures the forms of which corresponded equally to the outline
bands colored reddish
It is manifest these bands could not, (without wonderful chance) have existed previous to formation of pebble: were they not caused by the progressive action of heat as it penetrated the
other stone? This idea does not render the subject very clear (especially 1 & 2). I only noticed this in one place & it happened to be where the deposition from water owing as shown by arrangement of differently sized pieces, was most evident. —
Before leaving the valley of the Cachapual, I must notice the granite blocks described in M.A. Brongniart report to "L. Academie royale des Sciences" on the geological labours of M. Gay.1 Boulders of a white granite, with flesh-colored feldspar & black
is evidently mica (also a white syenite which stands in equal predicament with the granite) is very abundant (but not as far as I ascended so excessively so
396 verso [blank]
in the valley on all sides of the Baths of Cauquenes. Small pebbles are found on the plains of both rocks, even as far as S. Fernando. — They occur in the valley at considerable elevations, such as 2 to
400 300 feet & in places where the present streams could not have left them, viz. in a lake-like depression on one side. of the valley When M. Gay states no such rock is found within 20 leagues, he must be perfectly aware that in any direction excepting the Valley de los Ypressos he has not traveled 1/2 that direction. (People who have not seen the Cordilleras, may imagine that it is a simple narrow lofty chain of mountains, the nature of which may easily be examined: but the case is very different). The valley of the Ypressos however penetrates the Cordilleras obliquely, that of Yeos, (the two great ravines into which the Cachapual divides) is the direct transverse section. & this is the valley by which Pucheno crossed over from the Pampas. — Probably for this very reason M. Gay did not penetrate deeply into the Andes by this direct route. — How can he say, granite (& syenite) is not found there? especially when we know near St Jago not quite above 20 leagues to N. in the pass of Aconcagua & Portillo Mr. Caldcleugh1 assures me, there is plenty of gran granite & in his travels he mentions the numerous large fragments of this rock. — I have specified these particulars because M. Brongniart compares this case to that of the facts observed in the well-known Europe.
1 Alexander Caldcleugh (d. 1858), Private Secretary to British Ambassador to Chile, later trader and plant collector living in Santiago. Owner of copper mines at Panuncillo.
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(a) From general reasons I am strongly inclined to believe the sea, in the same manner as noticed in Patagonia (however inexplicable that may be) has carried these blocks from the central parts of the Cordilleras to seaward. — It is possible this might have happened before the elevation of the outer lines of hills, as mentioned at Baths of Cauquenes. — But
moreover there are some weak arguments for supposing has traversed in the sea has had possession of even that very part of the valley. We see in it on each side, at a height of about 80 to 100 feet a very narrow level but horizontal fringe composed of large pebbles cemented together (sometimes in horizontal strata) by a marly substance, or by carb of lime crystallized in stars (2245).
This is too abundant to have been subsequently infiltrated. I do not believe a mountain torrent could thus cement to stones with so fine a sediment. — Through the calcareous conglomerate the hot springs of Cauquenes bubble out. This fringe appears once to have been united across the valley, & that the river has subsequently cut through it & the underlying rock, where such occurs; indeed for a height of 40 or 50 feet on the rocky sides, the marks of
rocks torrent like attrition are very clear.
Nevertheless I am strongly inclined to suspect, this little fringe of plain is the remains of the bottom of the sea, when occupied this valley. — One would not dare to form such an hypothesis in any other country than Chili. —
I may also notice, that just above the little plain, there are irregular lines of great fragments of various porphyries, which do not always seem to have come
[sketch] A B C D E
Form of valley, where A & D represent the little level fringe. — & C as high as E the nearly vertical narrow gully, which the torrent unquestionably has worn in the porphyry where the R. Cachapual now flows & E to F the more inclined valley it has cut through the calcareous conglomerate.
[sketch] A C F D 100 ft. 400 to 1000 ft.
(a) Till every little ravine which enters the valley of the Cachapual was examined & he contrary proceed, I could
not never believe the presence of the block of syenite & granite was owing to any origin more remote than the central Cordilleras. —
from directly above: if the sea did not
deposit form this line the torrent must, when it flowed at a much greater height than at present. — How came the torrent then at one particular period to deposit, there the pebbles cemented with calcareous matter? & subsequently steadily, but most slowly corrode the exceedingly hard porphyries in nearly vertical gullies. —
I freely confess I place
to no great confidence in either of the above facts; but if granted this case will have more difficulty than every one, of which concern the transportal of boulders. —
I staid some days at Yaquil, near Nancagua: the group of hills ought to have been described, when discussing the granitic district. I reserved them on account of the separate subject of metallic veins, for which they are celebrated. — These hills form part of the first chain which runs parallel to the great Andes, immediately to the West of the plain at their foot. They are composed of quartz & feldspar crystallized, generally united with more or less of a chloritic mineral (protogine) (2257) (& 2258) from the lower parts of the mountain. this rock occasionally becomes so fine grained as to form an eurite (2259). This assuming a fine slaty structure & mica is used as a grinding stone. I did not however see it in its proper locality. — M. Gay says true granite is found in the neighbourhead & that it supports the sandstone passing into a puddingstone. — to the East we have seen plenty of the porph: breccia, which is, I suppose similarly
399 verso [blank]
These hills I could not trace any line of elevation amongst these hills: they appear to have assumed their present form chiefly from the effects of degradation. — Neither could I distinguish any stratification or cleavage. — The rock in many respects bears considerable analogy to that of Valparaiso, chloritic mineral however replacing the mica. — The rock is here also most extensively decomposed, it contains large boulder-like concretions of the same minerals already described; the small veins chiefly of quartz are excessively & are often parallel to each other, but run in all directions: the principal ones however seem to run in a North & South direction, which we know to be the general cleavage of the country. —
(a) The rock (V a) as at Valparaiso, is auriferous, but in a much greater degree. There are numerous small lavaderos, as well as true mines. — I received the following information from Mr Nixon,1 an N American gentleman, who owns the Bayos & Durazas mines. — The gold is found in quartz veins, but all the best mines it accompanies copper or iron pyrites: the former is thought most favourable to its presence. —
In the Bayos, the best one consists of a soft, friable mass of silvery, greasy, calcareous substance (2262), this contains minute crystals of iron pyrites &c &c; in the inferior (in value) parts of same vein a most curious assemblage of large cubical crystals of iron pyrites, masses of copper do. — regular hexagons of quartz & lumps of carb of lime are mingled together & cemented by the same calcareous substance. — Where the iron pyrites ceases, the gold is not found; specimen. (2261) shows the state of vein, when quite
1 Zacarias Nixon, an American who owned the gold mines of Yaquil near Rancagua.
(a) is traversed by several veins of a black micaceous-like iron one, & as at Valparaiso &c &c &c
Daubuisson1 on effects of vapour dissolving iron p 593
- 637 - 645, 647, 651
Frezier in his Voyage (7712 - 14)2 says centre of vein richest & intersection always richest part
N & S most common direction. Helms has incidental notice of N & S lines of some new [illeg]
Mr Buds experiment A p. 283
Read Fox on metallic veins [illeg] see last page Molina4
Lyell has quoted some French work
Speculation R.N. p. 78
Ulloa on Potosi mines R.N. p. 1066
Study products of Solfatara. lane of lead & silver, sulph of borytes, fluorine: How intimately ingredients of world must be mixed! In Europe & S. America in the same former wonder exposed in granular similar,
Humboldt. New Spain on metallic veins Mexico R.N. p. 1637
My theory of metallic veins R.N. p. 1658
L'Institut on various salts in metallic veins 1837 p. 2759
In Peru p. 166 to 169 to 171
Influence of forms of mountain on vein. R.N. p. 175 & 176
2 Frézier 1717.
3 Bud has not been identified.
5 Presumably Lyell 1830-3.
8 Red notebook.
profit-less. — There is much black stellated mineral present. —
This however is a much better case than when the iron pyrites is present but ceases to be auriferous it is then at once better to give up the mine. — At the Durazas mine, the gold seems however to follow the copper vein & just the reverse of what happened before, the coarse parts of
[illeg] vein (2260) with large crystals & prisms of plumbago, was exceedingly rich, the gold being in large, easily seen pieces. —
It seems, generally thought, that the
best better gold mines are rather superficial in their extent: some good metal ore has however been obtained from a depth of 300 vacas. — This fact may account for the quantity of gold in the scattered in all the neighbouring alluvium. — Does not Humboldt state the same fact, respecting the mines in the Ducal mountains? "Fragmens asiatiques." —1
All the best mines are here formed, by what is called a "Candelero" or "Cruzero". — The former is composed, of a large strong vein (a) containing small, subordinate, metallic strings or small veins not worth working ("Gias") crossed more or less obliquely (the more so, the better) by another small, but richer metallic vein. On each side of this line of this latter, within the walls of the strong veins (V nr 1 diagram) there is a mass of auriferous pyrites; or to express it, as the miners do, the stone of
the large vein "veta" by the effect of the little crossing [illeg] "gia", passes into an becomes infinitely more metallic in its nature. — There is much more auriferous pyrites in this mass, than in all the metallic strings together. — The included metallic
(a) These strong veins (or "vetas") may not contain any of the metallic strings. — one which, I saw, scarcely differed from the surrounding pegmatite; being itself of that nature.
The word "Gia" must be provincial. I cannot find it in Neumans dictionary.2 —
strings, can hardly be said to differ from those that cross the vein. — because it is believed, that they themselves only follow the vein for a certain distance, then leave it, at the same ∠, at which they entered & bend back to their old line of running!
This is shown in Diagram. Nr 3. — A "cruzero" is formed in a similar manner. (Nr 2), by the intersection of two (or more) good metallic strings with the strong vein & its parallel strings, in this case the whole included mass & for a short ! distance without the strings become metalliferous. — It may be also noticed, that this extends beyond the wall of vein, to the intersection of the two gias. — Although the richness of a "cruzero" seems to depend on the number & quality of the included gia & intersecting metallic strings; yet it is
finely believed that the quantity of metal in the cruzero cruzero is far more than that contained in the the composing strings. — indeed the diagram shows this. — It looks as if metal was actually formed at that spot, or secreted by the various strings, from the influence of their intersection.
The metallic strings are also believed to attract each other, that in a small one if running near to a larger one will be for a time, drawn into it. —
A third class of vein, is called "veta real" (Nr 4) & is most constant in its good quality; it simply consists of a metallic veins, included & permanently remaining in the strong one. These in this neighbourhead run almost
constantly invariably N & S; that is parallel to the cleavage; perhaps they rather form beds, than veins: the small metallic strings have no sort of determinate
402 verso [blank]
one vein thrown out of this course by the influence of earth which it crosses
I cannot help doubting this case. — I do not quite see how it is so known, because the strings are seldom worked
one vein thrown...crosses] not in Darwin's handwriting.
(n) A candelero, formed by it of a metallic Gia crossing a vein not metallic. —
Gia crossing a veta— called a [cimbara]
[secconal] view of the vein of the Bayos
Gias uniting in a vein or vata not in itself metalic
A Gia accompanying in a parallel direction a vein [burns] metalic is called a veta-[scale]
these in this ascent uniformly ran N & S or nearly so. —
x a [minahas] district
page not in Darwin's handwriting except 'Gias uniting in a vein or vata not in itself metalic'
direction. — Faults (Nr 5) are not unfrequently observed; they are said generally to occur, where the angle of intersection is large. — I allude to faults, seen by working a view where those which enter do not leave the vein at the corresponding point on opposite side. —
It appears to me this cause very similar to Nr 3. Showing that during the fracture which caused formed the walls the one vein, another was divided & pushed part pushed on one side. — I cannot answer for the accuracy of the above facts; but they appeared to me worth recording: their general tendency seems to point out some cause, distinct from simple fissure filled by distillation or infiltration with other minerals. — The gold ones are ground in the mills or "Trapiches", washed & the gold separated by amalgamation. — It is a curious fact, although often noticed, that this refuse of fine most impalpable powder, after remaining a few years exposed to the atmosphere, will bear reworking & give gold.
This process may be repeated 6 or 7 times, & afterwards it only requires a longer interval of rest & the same heap will again produce gold, although in rather smaller quantities. This
is the sole reiterated washing is the sole occupation of some of the poorer people. — An interesting process takes place, after some years in these heaps of impalpable powder. — much sulphate of copper effloresces externally, together with some earthy salts. — (which I lost): a section shows (Fig. 6) numerous polymorphous often angular pieces of dark colored substance, imbedded in a yellow softer sub material. The fragments (A A) are often several miles in
(a) in each dimension; are so compact, as to require a hammer to break them & are rendered very conspicuous from the surrounding matrix by a highly perfect & even laminated structure (as if fragments of slate). — I could not ascertain that this cleavage in the different patches follow any one direction. — This most curious brecciated structure clearly in an impalpable powder, could organize from some chemical action. — Fig. 6 is as exact a drawing. as I could make of a piece 4 or 5 feet square. —
On the rt. hand, some of the fragments were indistinct or blended together. — I should have stated, that this powder, after coming from the [trapiche] ground is first deposited in a pool,
from which is periodically cleared & these heaps formed. This described one was several years old. —
Before describing the tertiary strata of Chiloe, it will be well to consider some of the peculiarities of the external form. I have said in my Pri: Journal (p 469)1 that a chain of basins or small plains, generally connected one to the other, extend parallel to the foot of the Andes. That these basins are connected by broard flat valleys, to the sea, which are now water courses.
To the South of St Jago, the
plain inland plain or basin is connected with the extensive Pampas of the coast in the neighbourhead of R. Rapel. — From resemblances in the scenery, between this land & the inland waters of T. del Fuego &c. & other such reasons, the force of which no one can appreciate who has not seen the two, I have mentioned my conviction, that these level pieces in an alpine country are entirely due to the former residence of the sea. — Often when sailing about the intricate bays & channels in the South I had tried to picture to myself, what appearance this country, when elevated, would assume. — it was no ordinary satisfaction to have seen find in Chili answers to all my conjectures.
I will now give what more precisely geological reason I possess in support of these views & will describe the basins &c & their formation in order from the north-ward.
The valley of Quillota is a grand instance of one of the flat valleys. This water course bends where it passes the point of the Campana range but otherwise is tolerably straight. it is broard, many places being from 2 to 4 miles wide. the bottom is quite level & so abuts against the lofty sides it has a considerable dip to seaward, as shown by the torrent-like
1 This is a reference to the Beagle diary.
dotted lines boundaries of flat valleys or plains. —
road over the cuesta of corinca
2 3 4
there is a road in this direction
but I have never passed it
Lake of flaquia [illeg] 8
at Pelequia a road branches of towards the lake but I have only gone to it by Nancagina by the one dotted —
The Hacienda la calera belongs to the Late Presidente Sr Fco Luis Tagle, who resides on his Estate, and is about six leagues from Santiago. it is well worth your while to pass by it
page not in Darwin's handwriting. See Correspondence vol. 1: 406. From [Alexander Caldcleugh?] [28 August - 5 September 1834] [A map of part of Chile between Santiago and San Fernando, with notes on people and places to visit]
404A verso [blank]
cuesta dei strada
cerro de 600 or 700
estero de Payne
road to valp.o
St Francisco del monte
road to colahagua
Beluco belonging to the Marques de Larragon is 6 leagues from la calera — and aculeu is about 2 leagues from beluco, the lake is about 3 leagues from the houses of aculeu.
[map] [continuation of previous page]
baths of Cauquenes
mountains of algurez
a Mr Bruce formerly a master in H.M. Navy lives about a league and half from rancagua, if it be worth your while to visit him
To Sr Pedro [Terviola] comandante of the canton of rio claro, who resides on the estate of Sr T.ce Valdiviero [Second] advise you to visit, the estate is 3 leagues from rancagua — after you pass the canchapuel, rancagua is about
[map] [continuation of previous page]
road over the cuesta of corinca
2 3 4
there is a road in this direction
but I have never passed it
Lake of flaquia [illeg] 8
at Pelequia a road branches of towards the lake but I have only gone to it by Nancagina by the one dotted —
405 (part 4)
[map] [continuation of previous page]
V — S
The mines of yaquil belonging to Zacarias Nixon Esq. an american are half a league from Nancagua, and a road to the lake of Sagua Sagua passes by his house. Nancagua is about 6 leagues from Sn Fernando. To the Intendent of the Province Sr Feliciana Silva, who resides there I have given you a letter; also one to Zacarias Nixon Esq.
river, which flows down it. — The bottom is entirely composed of large round pebbles & evidently of considerable depth.
This is the character of all the
rivers valleys which conduct rivers flowing in this district from the Cordilleras to the sea. — such as the Maypo, Cachapual, Tinguiririca &c. — In summer their violence as seen by their beds is excessive; even in winter, when the I noticed quantities of sand traveling nearly as fast as the water. — These rivers are very shoal & broard; they do not generally cut any deep grit in the pebble bottom of the valley; neither do they frequently approach the sides of the & I believe their greatest effect is carrying forward the during the summer the enormous supply of fragments, which each mountain torrent in winter brings down. — I do not believe, they depend affect much the form outline of the flat valley. — In the valley of the Tinguiririca, which is has exactly the same form as Quillota. I observed there were large level bays or basins connected with the main valley (V Diagram Z) only a narrow mouth.
Where the improbability, (if not impossibility) of the river having been the leveling power is very great. — Yet at first sight, one would feel strongly inclined to attribute
the fraction of the valleys & the deposition of the great mass of pebbles to the rivers, which now occupy them. —
The exception of the valleys will
presently hereafter be discussed. —
The valley of Quillota in its higher parts, gradually expands
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(a) the beautiful basin Aconcagua. This place is perhaps about 8-10 miles in diameter; it is quite level, excepting a dip to seaward for the West; It is composed like the valley of Quillota of one great bed of pebbles. —
Whe The striking manner in which true basins abut against the very Cordilleras has been described in my Private Journal. fr Molina1 — Whatever has modeled this plain unquestionably formed the valley; their form & constitution is too similar to allow of any mistake. — In the middle of this isl basin there stands an islet island, separated from all other hillocks, this is composed ([sketch]) of strata of porphyritic breccia, which dip at angle of about 10° to the SW. It stands is quite separated by by some miles from all other such rock. A hill of this form & dip, could scarcely be thus elevated, whatever has rounded it, has removed the fragments, for the plain, like the a sea, surmounds it. — Must this not have been effected when a sheet of water did cover the plain? — no river could have this power. —
Facts of this class I have noticed in several other localities in the basins. — North of S. Fernando, there is a similar island but there the dip of the rock is directly to the East or Andes. Is it not probable that, the anticlinal parts of these hillocks have been removed?
Nea At St Jago, I have given my reasons for presuming that the pap of St Lucia was originally coated by other rock, than the greenstone. — What power but a body of water could resting permanently there, could thus fliece an insular rock. — When I say a body of water, I mean quite to exclude any
(a) This basin Aconcagua is said by Miers to be 2500 ft above the sea
of ro or debacle, (the common thought amongst the residents) for this, even if the powers of scooping & leveling be granted to it, cannot account for the enormous quantity of perfectly rounded pebbles. —
The basin of Aconcagua has no connection with any other: On the route to St Jago, after passing the high ridge of Talguen (continuation of Chacabuco) & some undulating country, where the former residence of the sea is rendered probable by extensive patches of a coarse soft sandstone,
of the history of which I am quite ignorant. — We enter the plain or basin of Guition, wherein is situated the village of Porpico. In a little valley, in the descent to this plain, there was an immense quantity of de silicified wood (sufficient to load a cart) some of the fragments were very large: they were mingled on the surface of the ground with others of porphyry & other crystalline rocks — I know nothing of the origin of this substance; possibly it comes from the disintegration of sandstone beds, such as just noticed at some height above. — This basin is separated from that of St. Jago by a quite a low (50 to 60 ft) ridges of [illeg].
But as this basin has a dip to westward & as the waters, I believe, do not cross the ranges of the Zapata & Prado, they must flow into the Maypo if so these plains are actually connected —a
little further to the westward than where I passed, the narrow separating ridge. Miers chart show this is the case. — As soon as this is crossed, we enter on the first of the chain of basins which extend far to the South parallel to the foot of the Andes. — The plain, on which the city of St Jago stands is between 1700 & 1800 ft elevation (numerous observations). This height easily accounts for the great rapidity of all the rivers; the The general height
(a) For the single [illeg] of all these basins. V. private Journal.
(a) of all the plains approaches probably to near this number of feet. — & this easily accounts for the great rapidity of all the rivers. —
The R. Maypo drains this basin: its banks in the South of the city are high & are composed of a mass of variously sized pebbles with here & there an enormous boulder: also horizontal lines of coarse sand. — At some distance from the river, there were lines of low cliffs, perhaps caused as the river retreated South & cut for itself a deeper channel: it is evident the river has had in this part a considerable influence on the form of the plain. & I believe both this & all alluvial action (a) only tends to destroy its regularity. The plain, although appearing from even a small elevation, absolutely level, really consists of long & most gentle undulations, which seem to correspond to the main valleys of the Andes. — This
would happens in any bay, where generally the water runs off shorter from every headland & deeper in the line of any great inlet. — The plain to the West of city is not quite so regular; it is chiefly composed of a reddish sandy, indurated clay, in some places containing many pebbles (c) in others passing into white sand: but every where there are imbedded many small fragments of pumice. —
Beyond Padaguel, (on road to Valparaiso, in same direction) such sand is capped by a horizontal thin bed of aluminous limestone, which is worked, in order to procure lime. This substance
(a) Perhaps, after the course of very many ages; the peculiar horizontal form of these basins & valleys will be obliterated, & then they will resemble the great valleys seen in every country? —
(b) Mr Miers states that the basin of Aconcagua is 2500 ft what is 700 above that of St Jago. — (The sea would probably leave these basins at different periods). —
(c) This sand is in place made of volcanic ashes. those parts of the plain to the West, where these finer sedimentary deposits occur are higher than where the pure gravel forms the strata. — The latter would appear to have been subsequently remodeled by either the action of retiring sea or river. —
is precisely similar to the Tosca rock of the Pampas of La Plata. — I could not tell, if I
had seen two was shown specimens from both localities, from which side of the Andes either came! —
As at B. Blanca. — the upper surface is most compact & crystalline; it is marked with stalactiform-like water lines, & contains minute extraneous particles; is cream-colored, the lower parts earthy (2240). This variety passes into quite white, friable pure calcareous substance (p.38). This formation demonstrates 386 that the plain is a regular deposit from water: this water must have been of great depth; for on the isolated greenstone hills (or islands) of St Lucia & St Christophal, on the very summits, there were many large fragments of rocks, united together by a white friable calcareous aluminous matter (2236) which
resembles is the same with the second variety described on the plain. —
St Christophal (by Mr Ecks Barom: measurement) is 946 ft above the Cristoval plain (or 2678 above level of sea). It is manifest the water once covered the summit of this rounded hill. — The Cerro blanco (
in the stone quarry for Sr Jago) is not nearly so high, but is equally isolated but if is partly composed of large fragments of a white harsh feldspathic porphyry (2237), a rock I have no where seen in situ, cemented by an abundance of similar calcareo-aluminous matter. — This mass rests against some of the common purple. Bre Porph=breccia. — It is almost certain, this rounded mass of fragments, must have been so modelled by the waters from a larger bed. Concerning the
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origin of these plains, a subject often discussed in St Jago
it only remains to show whether the water have been lacustrine or part of the sea. — We will discuss this presently. —
On the road to Valparaiso, after crossing the Prado, we descend into the basin in which stands Casa Blanca; this plain has according to Eck 811 ft elevation: it is connected by a "portezuela" or a doorway which passes over a low ridge with another basin to the South & this again by another "portezuela", with the level granitic country of the Maypo, into which the St Jago plain also opens. — This plain extends considerably to the North, & belongs quite to another series from the chain at the foot of the Andes. — Before the descent into Valparaiso there is an irregular plain called Plazilla; its elevation by Mr Eck & myself is 1050 ft. This is
very singular, on the supposition of its being a marine formation, as it lies to seaward of that of Casa Blanca. It may be lacustrine. — This plain is composed of beds of slightly agglutinated granitic sand, pale clay, green sandy do, & much coarse gravel, where many of the pebbles are very large. — the beds are horizontal.
In many parts of the neighbourhead, but chiefly in the water courses, there are found many fragments of silicified wood (2155). This is believed to be a process of the present day.
I had the satisfaction of finding rounded pieces, amongst the pebbles, which compose the lower beds of the plain:
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so that, at least, its petrification is anterior to the age of the "Plazilla". —
To return to the St Jago plain; looking to the South, it appears to
pass extend through a most remarkable level gap in the mountains, a true land-strait. — On reaching this angostura, I found it occupied by a river, the rapid tortuous course of which showed a considerable inclination;
(attached is a rough outline, of the country, executed from memory by major Sutcliffe, an English resident in St Jago, it very sufficiently shows by the white spaces the level basins.) —
The angostura expands into an
extensive plain, so extensive that to the South no land is seen to the South: it reaches as far as the village of the R. Claro & in the centre stands Rancagua. — Close to the north of the angostura, the river had worn a cliff, which showed the plain to consist of bed of gravel, capped by white sand, containing bits of pumice, appeared a regular water deposit. — I have shown that in the northern part of this 2d basin of Rancagua, the water flows to the North to the R. Maypo. — but shortly afterwards, without any perceptible change in slope of plain, the water flows to the R. Cachapel. Again in a similar manner in Southern parts the water flows into the R. Claro. — Close Beyond the little town of the R. Claro, there is an angostura, to which the plain comes up level; & then there is a descent to a small basin 30 to 50 feet lower; this 3d little basin
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on southern side itself contracts into an angostura, which precisely similarly to the first described, has a rapid river flowing from the 4th great basin of S. Fernando. This latter plain is exceedingly extensive, nothing but the snowy summits of the Cordilleras being seen over it, is said to extend at least as far as
Chillan Talca. — S. Fernando stands in the middle. — The northern part of this plain empties itself (as before) by northern angostura, whilst at a short distance we find the water flowing towards S. Fernando, to the South, from whence they turn westward to the sea: follow forming the river of the Tinguiririca. — We may consider these plains, either as four basins, as divided by the angosturas or land-straits, or as divided by the flowing of the waters, in which case the basins will generally be divided b a transverse line through their centres. — The basin of Aconcagua might have been of lacustrine formation, because there is only one exit; it would however be difficult to explain the broard mouth, & what power had leveled the valley & basin, into a continuous plain subsequently of course to the drainage of the lake.
But in these latter plains, whether we consider one large to have occupied them, or several distinct ones, we must suppose several
exits barriers to have been broken down at once, which is clearly absurd. But the The drainage, on the other hand, of these basins, on the
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supposition, that they were never formed by the gradual retreat of the sea, is quite
natural what might be expected, viz, that each channel, which entered the inland seas, would receive part of its water, during & subsequent to their retreat recession. —
I followed the valley of the Tinguiririca to seaward. — it bends up to the NNW: its bottom or plain is composed of a red, sandy clay, non-calcareous (like the tosca of La Plata), which contains
many or more more or less pebbles. I saw this substance also in the basin of S. Fernando. —
This valley expands in one place into a very large bay or basin, & near to this point bends to the northward & unites itself to the Pampas like country, which extends from the sea to the mountains west of Rancagua. —
The rivers here of Tinguiririca, R. Claro, Cachapel all unite & form the R. Rapel. — I shall soon show these great plains from their organic remains, are marine deposits; as the flat valleys ought properly to be considered as an arm from this plain, connecting it with the basins at foot of Andes, the same marine origin must, almost necessarily be granted to them. —
We ought not to be surprised, at the total absence of shells, in the
basins formations of the basins & flat valleys we must recollect that in the tosca formation of La Plata how exceedingly rare such organic remains & similarly where a mass of pebbles have been deposited
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by the sea, shells never seem to remain: Mem: East
most coast of T. del Fuego & Chiloe. — We may conclude, from the certainty that these deposits have taken place in deep water; from the impossibility of lakes having existed, from the knowledge that the same plains, never more to the westward, contain marine remains. — & lastly from the analogy of form of land of this country & the channels of the South, we may feel sure they have been leveled by the residence of the sea. —
I have been this tedious in my proofs: because it appears to me an important fact to show, that all the principal valleys & level plains even in
any one country have been once occupied & modeled by the sea. —
The tertiary plains in the
nea vicinity of the R. Rapel in their vegetation resemble the Pampas of La Plata, in their numerous escarpments of different altitudes & browed flat valleys, they are more like the plains of Patagonia. — In this part ( near not very far from head of R. Rapel) the formation does not differ much from that of the flat valleys. — generally especially in upper beds it consists of enormous quantity of pebbles & fragments imbedded together in some earthy substance.
Beneath this were very many
alte horizontal alternations of coarser & finer, harder & softer imperfect sandstones; here & there with a line of pebbles: — There were some islands of granite peeping up through these beds; it is probably owing to some such cause nearest the coast, that the plains & valleys incline inwards, or
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from the sea. — There probably was formerly here an inland sea such as
di at present divides Chiloe from the mainland. —
The numerous wall-like escarpements, place one
upon above the other, & the number of valleys, by the size of which are out of all proportion to the present streamlets, the levelness of the intersected plain gives to the country a very singular aspect. I feel no doubt these appearances can only be accounted for by the gradual retreat 2 & residence 1 of the ocean, & not as M. Gay st conjectures, by the breaking open of great lakes, formed during the upheaval of the Andes in the tertiary period, &c &c &c &c. — M. Gay states these walls are scattered excavated in many places by an infinity of open caves sometimes covered, sometimes open:
I only visited one of the Cueva del Obispo. This in its form resembles those in sea shore cliffs, a rounded cave terminated by two low horns. — the bottom is composed of loose shingle. the entrance is above the
bottom level of the valley. Could a better argument for the marine origin of these walls be brought forward? On the road from Navedad to Valparaiso, an elevated plain formed a line of escarpement or a lower one in the same manifest manner as in Patagonia. —
Reflecting on the effect, which centuries of weathering, would have on one of these step-like countries, it appears to me, from what I have seen, that where the lines of escarpements were not far apart, an undulatory country would be produced, such as most of the secondary districts of England. —
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(in the interior, I say under gravel sandstone of various qualities)
The plains, even those close to the coast retain an elevation from
6 to about 800 ft high. — a section of the lower half showed that the deposit is much finer grained & very uniform; I have, at first at a considerable height fi first noticed shells & the fruit of some plant. — The stone is a very soft yellowish, fine-grained earthy sandstone. (M. Brongniart call it Tripoli) is traversed by numerous thin plates or veins of ferruginous substance; there are also concretions of a harder rock. — A cliff from 100 to 150 ft. at the very mouth of the R. Rapel offered a better section: the stone is the same, it varied horizontally in texture to a very small degree. —
There were thin beds or rather lines of flattened concretions, partially connected, of grey, crystalline, calcareous sandstone (brecciola of Brongniart?) — in one part there was some gravel, which irregularly became very coarse, the pebbles were the usual metamorphic porphyries &c &c of the Andes. — I saw imbedded in the fine sediment one solitary rounded boulder of greenstone more than a yard square in content. — In all parts of the cliffs, occasionally numerous perfect & numberless fragments of shells were present. — The concretions contain the largest & most mineralised specimens. Pectunculus & Oliva are by far the most abundant in individuals, after this Turritella & Fusus. — There was much blackened wood in layers & some partially petrified (2227) which had been & penetrated by some marine animal. —
I also found fishes teeth, specimens (2220 ... 2229). —
With respect to the age of this formation,
compare M. Brongniart compares
In the English translation of Molinas History of Chili, there is said to be volcano at mouth of R. Rapel. In the Spanish it is said the sources, which is unquestionably the proper reading. — Dr Daubeny1 has thus been led into an error. —
1 Daubeny 1826.
it to that of Vicentin & says that many of the shells are like those of the tertiary period (what part of it?) in central Europe. —
The shells certainly appear to be more distinct from the recent ones, than those in the great Patagonian formation: yet the mineralogical resemblance, especially at S. Cruz between these two formations is strikingly similar. — This formation, although apparently older, than the Patagonian & therefore more time has elapsed for its elevation, yet is on the same level with it. — This can be accounted for, without supposing a less force of upheaval has acted on this side the Andes than the other; viz by the greater depth, as at the present day. of the
Pacific ocean on this coast than on the other. —
Is this caused by the N & S current removing the
[illeg] sediment which is brought to the coast. — Perhaps also from the other atlantic side, being more tranquil or less exposed. — This same explanation, perhaps accounts for the greater height of the plains of Mendoza (& source of S. Cruz?) over those of St Jago, in the h relation of 4427 ft to 1800 ft. —
Whatever may be the age of their tertiary beds at the coast, it does not follow that the inland basins were deposited at the same period; but rather, that the superficial parts at least are much posterior: it is impossible not to be struck with the identity of the tosca rock on both sides of the Andes: it, very probably, marks their nearly contemporaneous formation; & thus the plains of St Jago &c were deposited at same epoch with the Pampas.
that is probably posterior to the great Patagonian formation. — To which, as I have just said, I conjecture the beds at the coast to be anterior. — The extent of this tertiary formation plains to the South I believe to be great; to the
(Effects of elevation obliterated by earthquake wave suggesting Lyell in book true)
(On the prejudices on this subject A p. 4)1
(see Molina last page) & Miers
1 Notebook A, p. 4.
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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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