1835 Copiapò 127
[continues from previous section, DAR36.597-610]
& contains specks of hornblende, mica & chlorite. 3067 —
(La Puerta) Within this rock there are paps of true granite. (a) It is capped & succeeded on Eastern slope by a black micaceous rock 3068 (B), consisting of minute plates & grains of quartz. — This is penetrated by an extraordinary system of white granitic dykes, from the inferior syenitic greenstone, consisting of white well crystalloze feldspar & few specks of hornblende. — Some of these great dykes could be traced at intervals, following a direct line, amidst the succeeding formations for a distance of at least 2 miles. — This micaceous rocks, was were succeeded by grand hills of dark-coloured porphyries.
These on the Eastern side, began to show signs of stratification: which soon were developed into true strata (with high inclination to SE) of a much porphyritic breccia. — These strata are of great thickness from 1500-2000 ft. — They abut right against a gypseous formation, the beds of which are irregularly inclined at small angle to the West. — V. Section
To affect this there must have been a tremendous fault. — Yet such is scarcely perceptible in the outline of the mountain. — By looking at the section it will be seen, that this group of hills lie in a great synclinal basin.
(a) "La Puerta" so called from the valley being contracted where it passes through the conical hills of porphyry. —
(B). Is this a kind of mica slate? are the minute granules quartz or feldspar? if so the mica slate here holds its proper place in the system. —
1835 Copiapò 128
From the form of the stratification, I believe these hills the probable source of the subaqueous lavas, were bodily upheaved in the very trough of this Basin previously formed. — These unstratified hills contain are metalliferous: a silver mine, a silver mine [ponte & condentes] is worked in them. — Indeed every formation in this part of the valley abounds with metalic veins of gold, silver, copper, micaceous iron & I hear of lead & mercury. —
The gypseous formation here above alluded to consists of a red calcareous sandstone 3069, abounding with veins of gypsum. — These contemporaneous veins take the place of laminae. — With the sandstone there are some few layers of the calcareous compact black & green sedimentary beds of Potiero Seco. — But the red sandstone is far predominant (a) & replaces the other rocks & the mountains are all of a red color.
The valley towards Las Amolanas. runs in a very direct southerly line. — on each hand we have the gypseous strata, traversed by many faults, dykes & metallic veins. — The stratification is unintelligible: the valley however appears to be lie in a trough formed by irregular amounts of inclination in a grand westerly dip: — The strata, belonging to which I examined
(a) I believe this is the upper part of the gypseous formation perhaps partly supergypseous. —
1835 Copiapò 129
at the Hacienda of Las Amolanas. — Here the general dip is from 30°-40° to WSW: But there are over here faults of the kind represented in P 126, which render the ascertainment of the superposition not very easy. The lowest bed here visible is a of purplish black, crumbling base Porph. with few opake cryst. (This is the upper one of Porph. Breccia). — Is conformably covered by a coarse conglomerate (a), some hundred ft thick: the lower half white, the upper pinkish, — Parts consist of a coarse pale red arenaceous sandstone, in which a laminated structure is present (current cleavage) not parallel to the strata. —
Above this we have a very great thickness of thinly stratified yellowish siliceous sandstone 3074 3075: either smooth & quartzose or slightly granular: in this latter case, they are used as grindstones & hence the name Las "Amolanas".
In this there was a band of white & another very pale pink conglomerate, the cement being highly siliceous & union very perfect. — Some layers contained small white quartz pebbles: like the supposed petrified beans of the R. Claro. As I saw in the
(a) The pebbles chiefly porphyries, some jaspery & red sandstones.
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conglomerate a piece of mica slate. — This one is the probable origin of the small quartz pebbles. — In some places the sandstone, became greenish & less siliceous & closely approached in character those compact green stones of Potero Seco, which I believe also they replace. —
With the sandstone there are some layers of the black calcareous rock. — A neighbouring mountain is composed of the substance, to the thickness of some thousand ft. — This black stone & the yellow siliceous sandstone, replace each other & alternate to an uncommon extent. The sandstone however is generally the inferior. —
In the above mountain, the essential rock is this jet black calcareous, hard compact, non fissile clay-slate. 3070 — in some few cases, it is blueish & even green (a), but the fresh fracture is almost universally jet black. — The external surface weathers into a pale yellow or cream-colored substance. — hence from the general tint of the mountain, nobody would suspect there was a black stone present. — It is much stratified: the layers being
(a) In one spot the stone was more fissile, softer & aluminous & hence became a true calcareous clay slate.
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formed by varieties, more laminated, harder & with in a shattered state. In all these respects, the closest identity will be found with the similar ones which form the high crest of the Puquenes (St Jago). — Some of the strata are interlaced with gypseous veins: — There are a few several alternations of the yellow siliceous sandstone: part of which was coarser & contained fragments of shells. — Also one stratum of a red conglomerate. —
This rock mountain is however especially interesting by containing three or four strata, abounding with shells. — Where they occurred most numerous the rock passed into a brown limestone. 3073
In the principal bed in its upper parts there were thousands of a spiral univalve, of which I could find not one with a perfect mouth. Many of these must have lain dead at the bottom of the ocean 3058 ... 3066, for small oysters & serpulae were adhaering on to them 3110: in the lower parts the common gryphite was as numerous, the rock being almost composed of them. — In all parts (many Terebratulae) small oysters & fragments of a Pecten
1835 Copiapò 132
were scattered about. — I saw the impression of an Ammonite. & part of the "unequal" Bivalve of the R. Claro. — These strata are essentially gypseous formations, although gypsum is not here found.
They are seen to be covered by great thickness of strata & to rest on the Porph: Breccia. — The collection of fossil shells is moreover valuable as containing all the sorts. before re collected from different localities.
Part of the Escarpement of this mountain is very remarkable by the most extraordinary number of dykes. — I can only compare the appearance to the scratches made on paper by a child. or an irregular mesh arch of a Spider's web. Amidst the intricacy of branching, zig-zag lines, a very rough degree of parallelism might be observed.
The dykes are composed of very various rocks, almost all porphyries; some approaching to the character of syenitic greenstone: the commonest kind (a). has pale green base with large oblong cryst of feldspar & black crystals 3071, some of the latter being an inch long. 3072 — There is also much containing small white cryst of feldspar. — The vast numbers of dykes (& the fact may be taken generally
(a) The color of base varys. black. — dark green, light green & almost white. —
1835 Copiapò 133
in Chili) have little effect on the position of the strata. — It would manifestly appear that an upheaving force has stre[t]ched & cracked the hard strata, & that the melted rock has flowed into these crevices. — As this force acts generally in a linear direction, so have the cracks & consequent dykes a certain degree of parallelism. — This direction is generally N & S. — But the exceptions are infinite; indeed no form or direction of dykes, which can be well imagined are I believe absent in these Cordilleras. —
Lying above the strata formation already described, there is a vast mass of strata. I believe from 2000-3000 ft thick, inclined at about the same angle to the West, — These essentially consist of a bright red conglomerate: the interstices & seams are composed of a red sandstone with calcareous cryst. particles. 3095 3096 — The pebbles are well rounded, consist almost all of porphyries. & other crystalline rocks together with some sandstones. —
They are moderately firmly cemented together & packed in lines. — They vary from the size of an egg to cricket ball, some few larger, many smaller. —
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Hill, due W of House of Hacienda
Some strata are coloured purple. — In the coarse conglomerate, as well as intervening layers of coarse sandstone, there is very much silicified wood imbedded. — on the surface thousands of huge blocks are scattered about.
The wood has all been dicotylidonous: is now so perfectly silicified, that the structure is scarcely visible, is black, harsh & brittle. — Sometimes the stone is black & white in contorted bands, strikingly resembles in this case some varieties of siliceous mica slate: so as to require the lens the recognize its former origins is traversed by quartz veins. — especially in very centre of tree. — The concentric structure & rays of easy fracture from the centre are always present. —
The external form is generally perfect. — I found one tree 8 ft long with stumps of branches. — the end of another projected from the conglomerate. & was in diameter 5 ft. the hole being circular. — Part of another must when complete have been nearly 18 ft: in circumference. — The perfect silicification through such a mass of wood is certainly a very extraordinary process. — The spectacle of these trees of stone would astonish any one. — In the upper
after shells
([Chemenca] 110)
conglomerates
— trees
not uniforms
[encircled] Dikes
Thickness - granite conglomerate} Despobl
some of [illeg] sandstone}
place when trees grew}
subsidence. — from thickness } (Coquimbo)
amygdaloid pebbles porphyry
more mechanical [illeg] lower in the valley
sandstone in conglomerate & minor Porphyry pebbles
1835 Copiapò 135
part of the conglomerate there is 2-300 ft of red sandstones, containing only layers of the conglomerate. In upper part of this there is a stratum of the black calc. clay. slate: near to this, but in the red sandstone there is a seam with many shells. I clearly recognized the Gryphite, the spiral Univalve & very many of a Bivalve which I had not before met with. 3097
Again we had many of the calc. Red Sandstones: a Lilac Porphyry, which I really do not know whether it has been an injected mass or as it appears a subaqueous Lava. — Above this there are more sandstones & I believe the Black rock.
Whole mountain traversed by dykes of black Porphyries & white Feldspathic ones: (which probably proceed from underlying syenitic greenstone) & some of a most compact, smooth fracture, pale green base, with some obscure crystals. 3098 This rock is however singular by being marked with lines of variation, as if of deposition. parallel to the walls of the Dykes.
I noticed the same fact in same rock at the R. Claro in Coquimbo. — The red conglomerate is not universal even in this immediate district, either has been removed or not deposited. — In my note book I say "only one other cream coloured mountain capped by red lead sandstones" — [Copiapò notebook, p. 79]
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From the great thickness of intervening deposits, a considerable epoch must have elapsed between these & the gypseous strata. — Yet two species of the prevailing shells continue the same. — The red conglomerate, here replaces the compact sedimentary beds of Potrero Seco: & perhaps the calcareous white sandstones of the outer ridge. — We need not be surprised at this, when we consider, the extraordinary manner in which we have shown the black calc. clay slate, red sandstones & conglomerates, green compact sedimentary substance, yellowish white. siliceous sandstone. Gypsum with or without matter laminae replace & banish each other. —
The circumstances under which they must have been formed. will partly explain this. — We have & shall shown they rest on a great mass of subaqueous Lavas: the bottom probably was d uneven. & studded with nearly extinct craters. From there, siliceous calcareous & gypseous subs matter in solution would be ejected, together with volcanic ashes. — After a period, parts of the land, or more probably volcanos may would be were elevated, on which trees grew & from their coast pebbles & sands could be dispersed. —
Leaving the Hacienda of Las Amolanas, we proceeded towards the trifurcation of the valley. At the mouth of the Quebrado
1835 Copiapò 137
of Jolquera, we have section of lower part of Porph. Breccia. We have already mentioned its upper bed beneath the pale conglomerate — Beneath this are many purple & dull greenish Porphyries. Then a black hard semi=conch fracture siliceo-calcareous stone. 3076
Beneath which a coarse dull purplish conglomerate matrix is mottled colored, uneven fracture, crystalline, calcareous. 3077 —
All the pebbles are porphyries, excepting one of Granite. & this fact to me is unique in Chili. — Again beneath this some conformable beds of dark coloured rocks Porph. with few small red crystals. 3078 — After no great thickness of these rocks there was true granite; the axis of this grand band of elevation of Porph. Breccia gypseous & supergypseous formations. — The section of these lower beds, as is clear, is here very imperfectly examined. — I do not doubt compact sedimentary strata separates all the Porphyries. — I believe the Granite has here traversed the strata, & the whole section of this formation is not here visible. — It is a fact, which might in vain be sought for in central Chili, to meet a conglomerate with matrix non-Porph: within a few
1835 Copiapò 138
hundred feet of the granitic rocks. — The Granite is here traversed by numerous blackish purple dykes, is associated with syenitic greenstone & a Protogine consisting of white felspar & quartz with specks of Iron rust. —
The ravine at first runs in a N by East direction: the mountain rise on each hand. — On the West the white Protogine (Hill C) is capped by the dark purple, stratified Porph. Breccia. At its base there are patches of the gypseous strata which dip directly towards it. (a) —
These form upper parts of the Porphyries on East side of valley (Hill D), which generally conceals a range of (Hill D) Granite, which runs parallel to this first one. —
These little patches, in bed of valley, of the gypseous formation consist of the thinly stratified yellowish siliceous sandstone, containing some layers of the black rock, with the various shells as before very Gryphites. the "univalve" Ostreae, Terebratulae. Pecten, & in spots interlaced with Gypseous veins. — These strata are capped by thick mass of dark, claret purple, compact. heavy semi-cryst. Lava stone. 3079 — which is not uncommon in the country, is remarkable by containing globular or oval balls of size of egg
(a) Hence the granitic rocks are only exposed along a band in the middle of the Hill. — A little further to the North. — By rising of the gypseous strata, the granites are concealed & of course these upper strata must appear directly to dip beneath the very lowest of the Porph: Breccia. —
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to cricket ball. of same rock, but most wonderfully tough & difficult to be broken. — The sandstone vary in thickness from 20 to even 80 ft. — This is owing to irregularities in the underlying beds. — (a)
These consist of ordinary purple (not very compact) Porphyry abounding with crystals of feldspar. — On close inspection, the mass is seen divided into several beds (not very thick) by parallel bands of a harsh Porphyry. most highly amygdaloid. —
These clearly have divided separate streams of Lava. — It is interesting to find the gypseous formation. here almost banished by the abundant subaqueous Lava, whilst at a short distance, at Potrero Seco & Las Amolanas, there are several thousand feet without one such bed: It is a mere casualty, by exact mineralogical & conchological characters that it is possible to recognize the above sandstones. —
All these strata overlie, as I have said a mass of Porphyries, which rise into a lofty mountain range, being raised by a fine axis of syenitic greenstone (containing mica & chlorite). 3080 — This we crossed in a NE line & found it very broard. With This
(a) Are marked green & yellow in patches by Epidote. —
1835 Copiapò 140
rock varys in its character passing into true whole granite. — On the East side is succeeded by considerable slope breadth of micaceous slate. which it penetrate by numerous veins. — This slate with large layers of quartz, &c resembles all which has been described: it passes in parts into nearly massive ferruginous quartz, & in externally passes into a green, micaveo=chloritic slate. containing cryst. of feldspar & parallel laminae of quartz. —
The dip is not regular, being curved on a large scale, the prevalent dip is East. —
This formation is succeeded by a thick mass of the stratified Porph. Breccia formation dipping at high angle in same direction. — I in vain endeavoured to find an actual junction but failed. I suspect the mica slate has been bodily forced upwards through the superincumbent strata. —
In one place these dipped directly on to to a hill mountain of syenitic greenstone. with quartz. — But generally further north up in the ravine, I saw them dipping at a very small angle East & extending towards. the central part of the Andes. —
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Owing to the direction which the ravine followed, I did not think it worth while to follow it up higher. — This was some way below the last & solitary house of Castaño. —
Therefore here end the section. — I examined however some detached sections in this last Porphy. Breccia, which I will describe. —
One of the lowest rocks is rather a harsh, grey Porphyry: above this we had with cryst: of feldspar & which passes into a Lilac-purple cryst. feldspathic stone. 3082 — then many hundred feet of a al dull black. or mottled & greenish compact (cryst?) base. 3083 cont Porph. with few red cryst & passes into rock (litre 3086). This in its upper parts becomes purple: Is it Lava?? is marked with narrow red lines, which resemble lines of water deposition (perhaps decomposition). — A layer of red fine grained. earthy fracture. non calc. sedimentary deposit (like 3087) is covered by grand conformable stratum (which forms on side of mountain a lofty nearly perpendicular cliff) of a Lilac. non cryst. earthy fracture, base only occasionally Porph. with few cryst of feldspar. — This substance however, sometimes in the place of crystals appears collected in short waving lines 3084:
This is covered by many other kind of Porphyries. —
1835 Copiapò 142
I may mention in these compact rocks, an obscure columnar & large sphaerico-concretionary structure may be discovered. — In another section, a great quantity (& generally this is a common rock) of a dull purple or brown. 3086 base full of small yellow & red crystals. was divided into separate parallel beds by much (& this again is abundant) dull purple, semi-cryst base, highly amygdaloid with Zeolite (?). 3085
And these amygdaloid were themselves frequently parted by layers from 6-12 inches of bright red (non calc) fine grained, earthy fracture sedimentary rock. 3087 — There was a stratum 20 ft thick of a very compact pale sandstone, consisting of particles & minute rounded pebbles 3088 cemented in a yellow paste non calc: (a) — On this was 8 ft of the red sediment & then as before the dull purple Porphyries & Amygdaloids. —
In one spot in the vicinity there were many large angular blocks of true, purple & greenish. Porph: Breccia, where different semi=angular fragments were blending into one paste: hence such does occur here, although very rare, as in central Chili. — In the greater number of sections the Porph: Lavas far exceeded in quantity the intervening sedimentary
(a) Apparently small fragments of volcanic rocks
1835 Copiapò 143
layers. In one spot however a cliff of 300 ft in height, of hard rocks, with a crumbling fracture. — Far the most abundant kind is a very compact mottled rock which repeatedly varys in the tint of its color, is composed of red & green particles almost blended together. 3089 There were numerous thin layers of the whitish stone like (3088) & one of 20 ft of the red one like (3087). There was also one stratum of about same thickness of a reddish purple stony base Porph with feldspar & little nodules of quartz. 3090 —
The mottled rock, here & there contained a few well rounded pebble of different porphyries, as large as a mans head. — At the base of the cliff. these substances as usual alternated, with compact purplish Porphyries or Lavas. —
When viewing all the above sections, I could not help feeling a vivid surprise to find. strata, so deep in the grand series, which form the huge mountains of the Cordilleras, resembling (excepting perhaps in compacted) those which at the latest periods separate intervene between streams of ordinary subaqueous Lavas. —
Reviewing the coloured section, the part from the sea to the town runs nearly E & W. — From a little above this point to near the East end, the sections runs NW & SE: the
1835 Copiapò 144
very extremity turns up towards the NW.E. —
The distance difference of longitude from the Villa to the extreme point of Andes which I visited is only a little longer greater, than from it to the sea. — Of course the section is much longer. — yet even this is rather exaggerated.
The vertical height of mountains is of course exaggerated with respect to the base. & perhaps those in Andes, a little to those near the sea. — I have to remark with regard to the formations: — that the mical slate in Hill (B) is doubtful: (a) — all the feldspathic altered slate is also so. — if not so, ought to be colored pink: — The Porphyritic Breccia is different from those to in the central Chili: here it is clearly as formed by subaqueous Porphy: Lavas separated by sedimentary beds. —
Perhaps it would have been more accurate not to have drawn the gypseous & supergypseous formations distinct: my knowledge is not sufficiently exact to separate them in all parts. (b) — The total thickness of all the formations together (best seen at Los Amolanas) is I fully believe at least 8000 ft. — With respect to the stratification. — the lines of upheaval run within a few points of N & S. — I say lines but I believe they are very short ones. — Sections drawn E & W across the country at 2 miles apart, would differ essentially. — I except. 3 or 4 lines. —
(a) The geological position of the mica slate & altered slates is that the latter are superior, & immediately beneath the Porph: Breccia. — They are however closely connected. —
(b) It is quite a novel fact to meet the first escarpement of stratified rocks composed of the gypseous formation. —
1835 Copiapò 145
namely 1. 2. & 3. — perhaps 4 & 5. — There is a symmetry between (1 & 2) & (3 & 4). — The m other points of upheaval certainly have no great extent. —
The whole valley of Copiapò from the sea to the Andes is a mineral or mining district. [text in margin faint, illegible] — (sandstone 3128) These veins of Iron Gold Silver. Copper. Lead Mercury; which occur in all the formation. (a) — No where else do the veins follow so little any regular direction. — No where have I seen more intricate stratification, more numerous faults & dykes. — Yet the substance of the strata have not suffered so intense a metamorphic action, as those more to the South in central Chili. —
About a league above the town of Copiapò, a broard grand valley branches off first in a northerly & then NE direction, from the one already described. This valley is remarkable from not containing any water — it is hence utterly sterile & uninhabited & so nears the name of El Despoblado. —
The bottom is broard & level; it the shingle bed shows no sign of even having been traversed by a considerable stream, which the large dimensions of the valley would lead a person to expect. In the summer season, this line leads to
(a) The silver mineral of Chanuncillo is at the present day far the richest. — it lies a little way to the South of the valley. — Immense quantities of silver have been raised. — The ore silver occurs in a green sedimentary substance with red spots (3131) very similar to the rock at Anqueros (Coquimbo). — Much is in the state of a muriate of silver (3130). —
Fossil shells are found in the neighbourhead. — from thence I have a Terebratula (3133). — I hear of impressions of Ammonites. — It is said there is Limestone & much thinly stratified rocks. — From this & the geographical position there can be no doubt but what these mines occur in some of the higher formations. — N.B. — I have some green crystals from a copper mine North of the town (3129). —
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a good pass in the Cordilleras. — I followed the road to the first main ridge: beyond which it was not prudent to venture. —
I will not attempt to give a section of the line of road, the excessive confusion in the stratification would render this no easy task. & the geological structure is so similar, to that of the main valley, that it would not have been worth the trouble. — Shortly after having entered the broard mouth of the valley we left the rounder hills of the syenitic formation & soon entered then immediately arrived at the stratified rocks belonging to the higher parts of the series. X circular — Here, as in the other valley, there are alternations of fine red conglomerate, green compact sedimentary rocks, yellowish siliceous laminated sandstones with bands of pebbles; the black calcareous compact slate, which passed into a greyish Limestone full of pieces of gryphites & terebratulae. —
Some way higher up there was a section of about 1000 ft of the lower or Porph: Breccia formation.
(1st) The (1st) or the lowest bed visible, several hundred feet thick, or con dull purple conglomerate. (like 3118 3119 3120) — Breccia, smaller particles blended together, the larger quite distinct. The basis shows an obscure crystalline structure.
1835 Copiapò 147
2d well defined stratum 60 ft thick, of a pale dull purple ba claystone base 3125 (patches differently coloured) full of small crystals of opake feldspar & black cry mineral
3d. The Porph. Breccia as in Rio (1) great thickness
4th Harsh greenish grey base with numerous cryst of white feldspar & specks of Hornblende 3126. bed 80 ft thick superior & inferior junctions with the mechanical beds perfectly distinct. — structure strictly columnar. —
5th Porph. Breccia or rather conglomerate, for in these upper strata, the pebbles are well rounded. 30 ft. —
6th The same feldspathic Porph as in Bed 4th about 80 ft. Again covered by the dull blackish purple conglomerates. — In this section it appears to me that no one can question that the three well defined beds of crystalline rocks have been subaqueous Lavas. —
Near the point where the ravine of Santandres joins the valley hamlet of Paipote stood there are some unstratified Porphyry hills & a great deal of a rock, which more closely approaches to the character of the Porphyritic Breccia of Southern Central Chili X than any I have seen in this district. — The fragments are generally angular # although not some are rounded, the edges almost blend one into
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another: the basis is dull colored, often slightly purple with obscure traces of a Porphyritic crystallization. 3118 3119 3120
Here the stratification has been disturbed to a degree, which to my experience is quite unparalleled. — I have tried to represent one section. V Section (a) — The inner strata are thinly stratified red sandstone, the outer the above Porph: Breccia. The new is seen on a bare steep slope, & appears to be a section at right angles to a trough. V dike p 150
A lateral pressure from each side towards the centre must have been enormous. — for the lime layers of Limestone have a greater curvature than (U) a yoke. — On the right hand the Porph. Breccia gradually recovers itself, till it becomes vertical & then dips at a lessening lesser angle towards centre of trough. — On the left side, there are two such great & extraordinary faults, that it is quite impossible to understand the stratification.
Near here the valleys unite & are [illeg] suddenly bend; there has been great removals of vast masses. —
At the no great distance a large extent of strata are absolutely vertical. the disturbance is connected with the trough, but the manner how is as inexplicable as it would be to analyze the various directions of the forces in crumpling up & tearing a sheet of coarse paper. —
(a) There are contained beds of conglomerate.
[encircled] bottom
| Red sandstone | 400 |
| white [sandstone] | 300 |
| Jaspery rock trunk | 200 |
| red crystalline | 900 |
| 3 | |
| 2700 | |
| 2000-3000 ft ? |
several thousand ft of conglomerate
1835 Copiapò 149
As these vertical strata rise from a smooth piece of ground I measured their thickness by pacing them. Red finegrained coarsely laminated sandstone, which rested against a hill of the Porph. Breccia rocks 400 yrd. — white laminated do 300 yrd. —200 yrd of a rock the nature of which I do not at all understand; it is coarsely laminated, finegrained, dark claret color, semi-cryst. conch fracture 3122, heavy slightly calcareous stone. semi jaspery. It is joined on connected with another, which I do not know whether it is igneous & injected or subaqueous origin. — is bright red. high cryst. carb. of Lime & Iron with pebbles of green feldspathic rock & nodules of Agate! 3123 (a) I could not determine whether this substance occurred as a dyke or conformable stratum. — Beyond these 2700 ft of strata, there were from 2-3000 which I believe unite them conformably, but from intersection of valleys & irregularity of stratification am not certain.
Beyond these however there were several thousand ft of a quite distinct coarse hard red conglomerate. B (B) This conglomerate alone formed a mountain: is almost entirely composed of the debris of granitic rocks; in parts, large
(a) structure globular.
(B) I believe the total thickness of the strata above those alternations of Porphyritic Lava & altered conglomerates which I call Porph. Breccias is about 7000 ft. — This conclusion agrees with that formed in the main valley at Las Amolanas.—
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pebbles are loosely attached; in others the whole is most firmly cemented 3124, so that where the aggregate consists solely of crystals of quartz & feldspar, it might be mistaken for uninjured granite. —
It is not easy to conjecture from whence all this granitic detritus has proceeded: although it occurs in the area of almost each line of elevation in the main valley I saw none here. — Perhaps it may lie concealed & covered up at no great distance. In the conglomerate there are fragments of silicified Dycotyledonous wood. Both the nature & position of this formation strictly agrees with the similar one at Las Amolanas,
The cement is not calcareous: we may imagine the varying degrees of aggregation, depend on th a lesser or greater quantity of the silicifying fluid having percolated those parts. —
The whole of the neighbouring mountains are fissured & injected to an astonishing extent & which can at only be likened to the walls of the oldest crater, with dykes of a fine grained greenstone. 3121 I may observe that this rock. is far from commonly constituting dykes in Chili:
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Here however all were of this one kind: The strata must have covered as a surf cracked surface a vast cauldron of such fluid matter. — The dykes may be seen running continuously through across many thousand feet of strata: they sometimes arise from small hummocks of the greenstone. —
In the conglomerate, at close contact with the Dykes, I could rarely perceive the slightest alteration. — Sometimes a little green matter appeared to have penetrated & tinged (from volatilization) the stone is also [illeg] extends. to the depth of one or two inches. — The constituents parts of the conglomerate being granite would not easily be susceptible of alteration: but may we not suppose, at the time of injection that the whole mass was heated nearly to an equal degree? —
In another place I remarked so singular a kind of tilt as to be worthy of describing. V Sect. Two low ridge, which trended towards each other & joined at the had of a wedge shaped little valley, showed in front sections of strata dipping each to same point at ∠ of 45°. They were repetitions of
1835 Copiapò 152
the same strata upheaved in manner shown in P. 126. — This structure Such was the structure of the whole of the right hand ridge. But the left was more irregular & the strata by a succession of faults rose in inclination, as the ridge trended inwards; till from being vertical they leaned over at about 45° to the point opposite from the first & rested in the head of the right hand ridge. — This was rendered conspicuous by a central pale purple stratum; which was seen in various points along the left line. (a) — This will be better understood by twisting a slip of paper, through 135 degrees which is the enormous angular movement which the head of this ridge must have undergone. (B) —
Nearer to the Cordilleras, where the valley takes the name of Paipote, not far from Masiongo [word in margin very faint], there was as before various purplish brown & pale, purple Porphyries, some containing many opake Cryst of feldspar 3118, others with uneven fracture Porph. with imperfect cryst. & some extraneous particles 3117.
Again we have black Porphyries, with oblong & square cryst. of glassy feldspar. 3116 (d). — These alternated with various conglomerates & other sedimentary rocks, the all have been subaqueous Lavas.
(a) Its basest edge, showing a serpentine line, first on the left side, then on ridge & lastly on right hand side of hill. —
(B) I may also mention that I saw in several places horizontal faults. Viz. Line of fault [sketch]
(d) Also a branch, red, bare with immense irregular cryst & patches of feldspar. 3113
1835 Copiapò 153
Above the great thickness of the white thinly stratified sandstone I saw some of the "Plate" Porphyry (on oblong cryst of opake feldspar in green or grey stony base). —
In an irregular line of unstratified Porphy hill. There were some composed of a new variety, a compact conch fract, cream coloured base, with brown little dendritic spots & Porph with few imperfect cryst of feldspar. 3111
Another hill was exposed of white cryst of feldspar 3112 [faint words in margin] & black mineral from these immense dykes 10-15 yards wide of the same nature traversed the neighbouring mountains.
In another part I noticed on a hill, the upper part of which was obscurely stratified, the lower quite amorphous, but & partly brecciated in the same manner as a Lava stream sometimes is. — The same fact was several times noticed in the Cordilleras of Chili. —
After having mentioned such vast most quantities of subaqueous Lava, it may be well asked where are the volcanoes from whence they flowed? We will first consider what would be the appearance of the central mass in nucleus of a volcano neglecting
1835 Copiapò 154
both the stream outside at the base of the crater, as well as the envelope of the cones. The crater however in a subaqueous volcano, probably is of little comparative height. — Should we not have a great conical mass of unstratified rock of nearly the same nature, as the Lavas outside? If different kinds had proceeded from this one source, would there not be cones interspersed of such rocks? Would not parts possess a brecciated structure? Would not the upper parts, where the Lavas had within the crater overflowed each other often show a stratified structure? — Now it must be remembered, how universally groups of porphyry hill are found wherever I have traveled, that they are placed generally in a linear direction. — the groups being oval, & the longer axis being running N & S. —
All the circumstances, which I suppose would happen in the nucleus of a volcano, do occur in these groups. — I do not want to show that every hill of unstratified Porphyry has been a volcano; such rock might be injected amongst the strata, without any part having suffered eruption. — It may be observed that these groups generally occur in the [illeg][illeg]
1835 Copiapò 155
or on the borders of the principal lines of elevation & perhaps sometimes in the opposite or synclinal ones. — Now what would be the effect on an extinct volcano, constituted as above supposed. by an axis of upheaval crossing its centre. — Would not the envelopes of the crater (already of necessity of unequal texture) & the basal lavas be divided by broard fissures? Would not such fractured masses raised to a more exposed situation soon suffer degradation or be entirely removed? What would then remain but a group of crystalline hills & near to them regular strata of lavas separated by sedimentary matter? Another arguments besides plain observation may be adduced tending to show that extinct volcanos have been frequently the point of upheaval & violence, it is that in these groups, valleys frequently alter the course of valleys; although sometimes they appear as a point of reunion to the smaller arms branches. (a) —
The idea in itself is to me possible; that the point to where the volcanic energy has frequently found a vent, should, when such vent is closed, be raised by the injection
(a) omitted
Again I have repeatedly observed that that one or more of these unstratified hills will standing isolated or only partly connected with surrounding slate mountains. — Under any point of view, we must believe that the porphyries, which were formerly fluid, must then have had some support or encasement; if such has been removed, we are at liberty yo choose either an envelope, such as surrounds a crater or the ordinary surrounding rocks in the vicinity which had been thus upheaved: —
1835 Copiapò 156
from beneath of additional fluid matter. —
The fact is in accordance with the grand phenomenon, which has broken up the strata of the Andes as will hereafter be explained. — I am aware, that it is generally believed (Lyell — Daubeny) that dykes have been the conduits of the fluid lava from beneath to the craters.
I do not doubt that such a view is applicable to the subordinate mouths on the flanks of the great volcanos. — But the centre of Etna must present an entirely different phenomenon. — With respect to the dykes in these mountains I do not hesitate in saying they are mere cracks injected & that the greater number are subsequent to to the general cessation of volcanic emptions. — It has only been since examining the northern parts of Chili, that I recognized t in the origin of the porph: breccia formation, in an alternation of subaqueous lavas & their detritus. —
Hence to the South I did not carefully look to any particular connection between the hills of unstratified porphyry & the
Despoblado — stream
brecciated amorphous
2 cases of amorphous hills, but real cause of difficulty is [illeg] [illeg] & valleys.
1835 Copiapò 157
stratified Porph. Breccia. Indeed I doubt if from the extreme metamorphic action, such would ever be visible. — From many reasons, — the great inclination disrupted state of the strata — the probable height above the valleys — &c &c such would never be discovered with facility. — I have repeatedly seen such groups, gradually show signs of division into beds. — At R. Claro at Coquimbo (P 103) who can say, what was the connection of those subaqueous Lava, which now dip directly towards a h an unstratified hill consisting of various crystalline rocks?
In this valley, there was one section, V. Sect. (1), where I believe I distinctly traced for several miles in length a great bed of purple Porphyry, overlying the usual alternations, till it joined on to an irregular mass of hills. — I have drawn only the half of the section; — on the right side, the appearance was less clear. —
I likewise saw another interesting section V. (2) from a distance, at the corner of a great headland, on one side, a great thick bed
[sketch]
[This sheet is excised from the Despoblado notebook, pp. 29b-30b]
Strata at varying dips. — I can only look at this spot as a Volcano: — (NB the junction of valleys seen often to occur in midst of Crystalline Hills) Also another Bluff point (1) where the appearance does not seem that of injected rock — but rather of the stream of very red Porph— which have had sedimentary strata deposited between a part of: therefore the bluff part must before upheaval have been near the Volcano —
[added in ink] P. 158 Copiapò
1835 Copiapò 158
of purplish rock overlaying the usual banded mass; on the other (left) side it bifurcated, each arm thinning out; the lower one being the shortest. — Its superior position & general appearance induced me to believe it was not injected; if so the point of eruption must have existed somewhere near to the corner: & between the ejection of the two streams, part of the lower one was covered by deposits. —
At the foot of the Primera Linea, so called from dividing the waters which flow towards the Pacifick from those which enter a basin on within the Cordilleras. — From the difficulty experienced of respiration, scarcity distribution of vegetation & coldness on these heights. I should suppose the elevation must be about 10000 ft. — At the foot there are inclined strata, of the white sandstone & limestone containing 3127 gryphites, Terebratula & (R Claro) unequivalves.
Above these there is a grand Infaceous deposition many hundred feet thick. It is divided into two great horizontal beds: the lower
1835 Copiapò 159
is a very pale purple, slightly harder, 3114 & the contained fragments smaller, than in the upper which is white, contains numerous scales of mica, & grains of quartz & other crystals. — also many small fragments of granite (perhaps ejected from crater), but 9/10th of the fragments which are very numerous, are angular & of all sizes of a grey vesicular Trachyte.
In the upper part I noticed some rounded ones. Some distance further down the valley, the tufa is finer grained, tinted with Lilac very little specific gravity, yet appears compact straight fracture & sonorous! under the hammer. 3115 — The upper bed from its greater softness is weathered into groups of strange & sharp pinnacles, which marks on a large scale the former frozen snow, which assumes when wintery beneath the sun. — This white bed is covered by other of a darker color, about 200 ft thick, the junction is perfectly horizontal & even; I do not know its nature, but it is not
1835 Copiapò 160
hard rock. — These thick horizontal strata form on the summit & edge of the Primera Linea the edge of an apparent plain. — To the South, above this level, there are some rounded hills of a red color — it is possible these are the ancient sources of the Trachyte.
The tufa caps all the neighbouring mountains, — it has a slope, which is just perceptible to seaward or the West,
In the same direction the strata grow then be thinner & as we have shown finer grained. — It is seen many leagues distance occasionally capping the hills. on either side of the great valley by which we have ascended. — The summits are always level & the heights at distant points always correspond as if once they had formed parts of one plain.
At the extreme west point, where I saw this formation, its elevation is probably about the same as the plain of shingle, described
1835 Copiapò 161
as forming a high plain South of Potrero Seco; from this height it slopes upwards to the great elevation of the Primera Linea. — It cannot be doubted but what this tufa, is a regular aqueous deposition; its mature. horizontal stratification & position prove this. — When the central ridges of the Andes were just above water & the outlying most lofty hills, were low Islands, then at a short distance to the South great masses of gravel were accumulating, whilst here near to some Trachytic volcanos the tufa was precipitated.
It is by no means necessary to suppose all the patches of tufa ever formed one unbroken plain. — if such was necessary the degradation would must indeed have been immense.
Mem. the valley of the Patillo, how immense the excavation!
I do not doubt such has taken place to a great extent; & I shall be able to bring some presumptive evidence, that the sea that chief agent in destruction subsequently occupied, with one of its
1835 Copiapò 162
arms the valley of the Despoblado. — I have described, the summit of the Primera Linea, appearing as a broken plain; whatever its extent may be, the road is said to soon to descend on the other side. (B)
It then enters on an extensive district from which there is believed to be no drainage. — A little way North of the road, there is a dead level & most dreary plain, which in length is a two days journey for mu loaded mules to pass. 15? leagues — Is said to be covered with rounded pebbles. & at the center one end there is a large shallow lake several league long, which in the summer drys up & leaves thick stratum of pure salt. (a) — This is quarried & carried down to Copiapò. —
I have described the Tufaceous formation & surrounding country with particularity, because the fact of a great horizontal deposition elevated to so great height & which from its position must be of submarine origin
(a) The salt is of excellent quality: the margins of the lake are deep mud, the mules enter by a strip of hard land to some distance within, where the salt is preserved with crow bars. —
(B) The Cordilleras are described as being broard; it is necessary to cross a central ridge, before reaching the Eastern slope.
1835 Copiapò 163
is most important. — It shows in this neighbourhead that all or nearly all of the general & violent angular movements, which the strata have suffered. took place, before they had risen from the deep sea. —
It shows that from 8 to 10 thousand feet of the present elevation of these Cordilleras above the sea, has been effected without sensibly altering the relative position of neighbouring points. — no doubt the tufa was deposited with a gentle slope to seaward & with such it now remains (a).
Independent of these considerations, there is an interest, from the extreme variety, in finding any volcanic formation, in Chili, the beds of which are not parallel to the great mass of porphyries.
This would appear to be the southern limit of an a grand volcanic formation — I must however except the Cerro de L'Arusse, a mountain a few miles to the South, where in summer sulphur is quarried & which I believe to be an extinct
(a) This conclusion is in perfect accordance with the argument drawn from the continuous slope of the terraces of shingles in the Cordilleras of St. Jago. —
1835 Copiapò 164
volcano. — Mr Lambert in an obliging communication which he sent me, after talking mentioning the Quetrada de la Copa, which branches off from that of Santandes (north side of the main valley of the Despoblado) continues "You travel upwards in that dry ravine for about 3 miles, where it ends, & on the summit of the hill which forms its boundary, you find large superficial beds of sulphur & the sulphate of Alumina. — In the ravine there are scattered about fragments of Pumice Lavas calcionic granite & porphyry & other volcanic productions. — The formation of all the country from Sant Andres is generally of granite & porphyry covered by volcanic eruptions. These substances present generally a red appearance, whilst the granite & porphyry formations on which they lay is black. — There are many points, where you can see the points of the granitic hills rise in the middle of the volcanic formation; the Lava not being in sufficient quantity to cover the whole. — All the ravines have been formed after the eruptions of the Lava. (a) — This volcanic formation extends
[C. S. Lambert to Darwin [c. July 1835].
(a) from Copiapò to Atacama, forming in some places regular basaltic elevated plains. These detain the waters which flow from the western side of the Cordilleras & cause those salt lakes, where the inhabitants of Copiapò & Atacama provide themselves with that article."—
It must be remarked that Mr Lambert states that the volcanic eruptions capped the hills prior to the excavation of the valleys in perfect accordance with the idea that the tufa in submarine formation [more text illeg]
1835 Chili 165
Valleys
In my journey from Valparaiso northwards I collected some facts respecting the elevation of the land, figure of the valleys & some patches of Tertiary formations, which are so intimately connected that the must be described together. —
49 Valparaiso Paper
Mr Broderip has fossil shells from Coquimbo from Caldcleugh
I have formerly noticed the beds of recent shells at Concon. Quintero & in all that part of the coast, which are worked for the sake of being burnt for lime. — Beyond the village of the Plazilla, there is the exact form of a good sized Bay. the surface is thickly strewed over with immense quantities of comminuted shells. —
packed in layers
Again a few leagues beyond this, near to Longotomo Catapilco in very many places the hill tops are thickly covered with layers of broken shells. — These occur in quantities as in Quiriquina (at Concepcion) & coat the slopes & smaller vallies as well as the summits.
I should think the elevation must be nearly 300 ft above the sea. The soil is very sandy & in the road from the wear & tear the shells are minutely comminuted. — Hence
1835 Chili 166
Valleys
some have supposed, that they have been carried inland by the force of the winds.
When undisturbed the shells are frequently packed in layers & amongst them are many nearly perfect & large or heavy ones. — The commonest kind is the Quintero Donex. —
The valley of La Ligua is bordered by perfectly level plains of gravel of some height. — On the north side, those extend to & separate it from the valley of Longotomo. This plain is divided by many broard flat valleys, like those in Patagonia. — At Longotomo a grand level conducts a most diminutive trifling rivulet to the sea. — Where I crossed it, the distance from the coast is about a league & a half. — The whole surface is partly composed of broken shells: The Guassos assured me it is a general circumstance & called attributed their presence to the Deluge. — On the North side of the valley, (to the height of about 200 ft above the sea) there are immense quantities of shells, which on one side of the road are tolerably perfect:
1835 Chili 167
Valleys
They coat the surface of the side ravines: hence we must believe the action of the sea has modelled carried leveled even the minor inequalities of the land.
At P. Ligua
On the coast, where these vallies enter the sea, Mr Chaffers saw the shells about 50 ft high (chiefly Concholepas) quarried for Lima. —
Near Guachen some slate rocks are smoothed over with by a gravel plain, which abuts up to the base of a higher & more extensive one. — Some shells on the surface
Valley of Quilimar. much shells, but when I saw them only about a mile from the Beach close of Conchalee or South side two very distinct (terrace like) plains, the lower one is about 60 ft high & is suspended by some flat low land from the dra. beach. On the surface immense quantities of the common shells as on the beach. — Large Concholepas. Donax & Venus.
At this point I turned inland into the interior & more elevated country, so that I met with no more shells till near Coquimbo.
The valleys however of the R. Chuapa & & Illapel are bordered by extensive & level plains of stratified shingle. —
(a) If there had been any doubt concerning the origin of the step-formed plains, such almost alone, would have removed it.
1835 Chili 168
Valleys.
Traveling from Punitaque to the valley of the Limari there is an extensive level plain, many leagues broard, which separates the more interior ranges from the coast one. — This plain forms southern border of the above valley as soon at Tuqui or Ovalle. — within its margin there is a second large terrace through which the course of the river lies. Both plains are seen to consist of shingle. —
From Tambillos to Coquimbo a large valley expands. into what with propriety may be called a dry estuary. — it has no regular stream, is quite level & near the mouth several miles broard. — The southern point (La Punta) rises exactly as a headland does from the sea. —
The plain into which the aestuary expands is very extensive & I believe is united with those inland ones which extend to the south of the valley of the Limari. — On the west hills arise out of it, like Islands: beyond these we have the low plain, which fronts the sea near Coquimbo. —
I have stated the above facts with particularity
1835 Chili 169
because it will be seen, that in every valley between on this space of more than 200 miles of coast, there are proofs or presumptive evidence of the sea having occupied each of them. —
The Coquimbo plain has a length of about 11 miles, it extends from some miles north of the town to Herradura Bay & forms only a fringe which sends off arms amongst the hills & one long one (bisected by the river course) up the valley of Coquimbo. — We have already shown how it is united by land straits with one extensive plain in the interior. — The average height is from 2-300 ft. (a)
Its constitution differs exceedingly in different parts: in the mouth of the valley of Coquimbo it is 358 ft high & appears entirely composed of stratified shingle: whilst a short distance to the South the point (where no valley has brought coarse materials into the from [illeg] sea) the finer sediments only covering a few incidental layers. — The plain also being 100 ft lower. In many places the upper surface, instead of being of rounded gravel
(a) & the whole connected in one unbroken & scarcely perceptible slope.
1835 Coquimbo — Tertiary F. 170
is covered by a hard calcareous stone called by me Tosca rock. — The escarpement of these plains is frequently double & even treble; that is fronted by narrow step formed terraces.
At the mouth of the River, this structure is very complicated & will be separately described.
At Herradura there are some good sections of the lowest part of the formation of the Plain — it consists of fine grained whitish sand agglutinated into a soft sandstone: there are patches of yellow sandstone & whole is irregularly &much marked with ferruginous matter. (a) In these strata, there are lines of small thin concretion of a very hard & dark lower calcareous sandstone. These concretions in places are particularly united & form a stratum. —
The fact occurs as often described in the Tertiary formations to the South. In these concretions there are abundant shells, the composition of which has been considerably altered. — The most abundant kind is a large Pinna with a [illeg] margin & the large oyster, a fossil, so
(a) Here & there is scattered an occasional pebble of the surrounding granitic rocks
1835 Coquimbo Tertiary Form. 171
conspicuous in Patagonia, & several other shells, Carium. Venus. Turritella. 2802 ... 2811 & 2813 ... 2818. There is a small species of oyster which is not an found in other locality. — The most remarkable occurrence is however, the surprising numbers of huge silicified bones: from their size they the greater number manifestly belonged to cetaceous animals.
Above the sandstones, there is a considerable thickness of stratified shingle, with some calcareous matter; the pebbles coming passing come from the neighbouring hills: in the middle of this there is one thin stratum full of the large oyster shells. —
These depositions must have accumulated in a basin, formed protected by some the ridges of outlying rocks. —
There are here two little plains, on the surface of the lower one there is some gravel cemented by white calcareous matter, the age of which is much more recent: the contained shells are the same as those found on the beach & some as the common purple Trochus 2819 2820 partially retains its color. — The above section is of no great height, above it & lying on the sides
1835 Coquimbo Tertiary Form 172
of the ridge of Syenite, there are some shells. generally broken, such as now occur on the sea-beach. — the commonest being the Concholepas & the Turritella cingulata. — A few of these were united by calcareous friable matter; so that there can be no doubt they were not carried there by men. —
Yet in many favourable looking spots, lower down on I could not find the smallest fragment. — The elevation is 242 ft. Barom: —
Near the port of Coquimbo, the face of the escarpement is in many places covered up by considerable mass, at a small elevation of sand, stratified or slightly agglutinated, abounding with shells, of the same species & in the same proportion as are now strewed on the sandy shore. — I saw one narrow mine, with steep sides. which ny person would at once suppose had been excavated by running fresh water. In it however & abutting right against the older soft sandstone, there was a wall of the newer stratified fl full of the common shells. [sketch in margin] — Hence the sea must have excavated this ravine & subsequently partly silted it up again. —
1835 Coquimbo. Tertiary Form 173
Following the same decretion inland for about a mile & a half, you ascend to the back of the plain. The elevation is 252 ft. Barom: The surface is here composed of a hard cream-coloured aluminous. stalactiform limestone. 2928 the kind which I have called Tosca Rock. It is marked with horizontal lines & overlies & passes into a whiter more friable kind. 2929 —
The upper hard kind sends wedge-shaped veins into the less compact stones. — The whole stratum precisely resembles the Tosca rock of the basin of St Jago & the plains of B. Blanca & [illeg]
(a)
Occasionally this stone is quarried to burn for Lime. — Beneath the Tosca, there is a stratum about 20 ft thick of a stone called "Losa", which although hardish & brittle is used as a freestone. — It is essentially composed of small fragments of shells, minute pebbles, & oblong small hollow grains ( (some of small seeds) of white calcareous matter 2930; firmly cemented together. — The structure of this rock deserves examination. — 2924 ... 2927
In it there are occasional well rounded moderately sized pebbles & a good many shells. —
(a) omitted
There is a remarkable exception in this containing shells; although I have such great extent of surface abounding covered with this substance, I have no where else seen even an imperfect cast of a shell. — This general though not universal deficiency is not of easy explanation. —
[in pencil, very faint] A short description must be given here (below) ( or elsewhere) of the conversion of upper layer into stalactiform rocks because such a discussion has been alluded to in K George Sound.
1835 Coquimbo Tertiary 174
A short distance south of the town (a), the edge of an escarpement has been extensively quarried for this Freestone: There the mineralogical nature & position is precisely as described:
I extracted various shells 2789 2790, a circular Calyptraea & Donax, Turritella, Venus & Trochus with tint of its color, &c at one Concholepas.
I no where saw a fragment of the gneiss, oyster or Pinna &c of the lower series. —
All the shells collected in the Tosca are similar to what are now found in this neighbourhead; but their relative proportions appear decidedly different. One of the commonest shells, a large Calyptraea striated from the crown to margin, which is now excessively numerous I could no where see in the Tosca. — In a like manner, the common Concholepas & Pecten are both very rare. —
Both here & on the 252 ft: plain, there are shells lying loose (or imbedded in calcareous and) which appear much fresher. — In the latter place we had numerous fragments of a common Mytilus yet retaining its this tinge & of the Concholepas. — Here is a much closer similarity
(a) I am not sure the elevation of these quarries, which are sub situated on a step formed fringe to highest part of the plain, is exactly equal to the 252 ft plain. — They are clearly contemporaneous. —
I should mention that the superficial Tosca Rock abounds on the plains a few miles North of the Town. —
1835 Coquimbo — Tertiary 175
to the present proportionate numbers. — A perfect identity however, where the large radiated Calyptraea abounds &c is only found in the stratified sand, already mentioned. — It may be observed that the elevation of these the loose shells. viz. 252 ft. only differs 10 ft from the measurement of one occurrence in Herradura Bay. —
It is I believe the highest point, at which recent shells can be found in this neighbourhead. —
The slope of the plain here to seaward is not solely formed by degradation; for on its edge the strata of Losa dip in that direction at an angle of 10°. — There are here parallel furrows at right angles to the line of dip. — To the Eastward (& seaward) the the strata & plain are horizontal. (a) Is this inclination owing to upheaval? or have the strata been deposited on a slope, across which furrows were formed, as in the sand on a Beach?
To continue with the section. beneath the lower margin of the
(a) At the time I was at a loss to understand these furrows on crossing the gently inclined strata; since but having seen a similar structure in a beach lately constituted in the Coral Isd of Keeling; it appears that the layers of sand are successively added to the face of a more or less inclined beach: these being cemented, the layers probably would not all have an equal hardness, & then on degradation we should have furrow crossing the edges of the strata dipping to the bed of the former sea on the shores of which they were accumulated. —
[sketch] ocean hard hard
line of subsequent degradation
This view of the structure perfectly agrees with the belief of the calcareous matter having been accumulated loose on the shores. The imbedded shells are likewise littoral. —
1835 Coquimbo Tertiary 176
Losa blends with & tinges white by its calcareous matter a coarse ferruginous firmly cemented aggregate of broken shells. — In parts this is more arenaceous; in others it contains a few layers of pebbles & others of yellow & brown thin strata of a very fine grained aluminous sandstone.
The fragment of shells, almost exclusively consist of small pieces of of come from species in the family of the Balanidae; the chief kind in the great Piton; there are a few other shells, commonly fragments of the common Pecten. 2798 2799 2800 2801
This aggregate strikingly resembles in composition the formation at Pt St Julians in Patagonia.
In another part, there were great numbers of a small oyster; some of which were still adhaering to large imbedded angular fragments of an Hornblendic rock. — This same oyster is found in the lowest strata, with the great one. — amongst the living species of shell, collected here, there is one small kind, perhaps it may be the same: but it is said to be very rare. — This shell, the
(a) the nature of the shell is partially altered. There was a fragment of bone in the same state. —
1835 Coquimbo Tertiary Form. 177
common Pecten & a large smooth Mytilus are common to all the intermediate & lowest divisions (B). — These strata which are intermediate between the upper calcareous & lowest sandstone ones. have also an intermediate zoological character. There is however no marked separation: as even the few accompanying specimens will show. — The shells (2791 .. 07) which were found 2791 ... 2797 where the great oyster & Pinna were present, but still uncommon will also be useful. — Perhaps there is more difference between the intermediate & calcareous, then with with the Lowest strata. —
[sketch]
| Superficial shells: 252 ft — | in nearly same proportion | ||
| calcareous Tosca Rock | Recent shells not in same prop. | ||
| Losa | grain with shell | ||
| sometimes represented by shingle | Intermediate strata |
Terti | |
| Give the sedim. in Tert. geology | Lowest series Great oysters & Pinnae; silicified bones in concretions |
Shells as on the Beach | in same proport. |
| Level of the sea |
[writing in margin] [illeg]
On the surface of the plain we find shells, as now lie on the Beach; but the proportionate number were strictly preserved in the patches of sandstone at the base. — In the superior calcareous strata, we have recent species, whilst in the lowest there are some (a), which certainly are not found
(a) The inhabitants say so. —
(B) The Pecten occurs in all the three divisions. —
[map]
1 mile
B. Coquimbo
A F A A F
Coquimbo
The sea
B C E F
Dry shingle plains
Low swampy ground
La Vega
F S
1835 Coquimbo Tert: form: 178
in the neighbourhead, probably from being extinct. Such species do not appear in the intermediate strata, which by a gradual mineralogical passage connects the two series. — I cannot well imagine a more gradual order of change.
To conclude with this patch of Tertiary formation; at Tongoy about 20 miles to the South I heard of similarly constituted cliffs, containing shells & silicified bones. To the North it appears in several parts of the road to Guasco as will be described. —
Parallel Roads
the parallel roads at Coquimbo have been described by Capt. B. Hall & their origin discussed by Mr Lyell. — The valley of Coquimbo may either be considered as formed or bounded by the irregular hills of unstratified crystalline rocks or by it may only include that part within the lines cliffs of the highest plain & which contains the parallel terraces & river. On In the former case the valley is wide, but certainly not more than half the 7 miles which Capt. B. Hall gives. In the latter (or true valley) its average width is about a mile. This will be better understood by looking at the accompanying rough outline chart. [page 662A]
1835 Coquimbo. Terraces 179
The plain, which is, as I have said an arm of the one so minutely described, lies chiefly on the South side of true valley. — It is apparently perfectly horizontal, its margins are deeply indented & steep: it becomes grows narrower. higher up the valley. — I presume it is the one mentioned by Capt. Hall as having been "just tipping with the waters edge". — This plain forms the highest of those parallel & level lines which strikes the eye of a stranger. —
The step-like terraces abut against its foot. — A section Sect. 1 drawn from the sea, through the city to the high plain; first gives (A) a level piece of ground, in many places swampy, about a mile broard, yet from water drainage has a small fall. — surface strewed with marine shells.
This plain forms the base of true valley, & on its level the river pursues its course. We then have a low escarpement, which closely borders the town & is perhaps 30 ft high. — On this little plain (B) the chief part of city is built; a central house is 65 ft above level of the sea. —
Towards the eastern suburbs, there is another es line of little projecting escarpement of similar appearance. On its plain (C)
1835 Coquimbo — Terraces 180
there are a few houses. (C) — Then we come to the third & much higher escarpement, its base I aestimate to be 120 ft above the sea. — It is surmounted by a more narrow terrace-like fringe, which skirts the highest plain. — Yet from its (E) levelness & distinctness forms a decided step, height 302 ft. — Above the fourth little escarpement there is the extensive plain, (F) here 364 ft above the level of the sea. —
It will be seen there are four escarpements: the one between plains (C & E) being the highest, a short distance to the South there are some appearances of an intervening one. — The plains, or terraces are five in number: it will be seen how they all sweep outward, round the headlands of the mine true valley & face the sea. — Respecting the marine origin of the main plain & the low swampy ground there will be no question. — From the locality I could not examine the two flats on which the city stands; but at two miles distance to the South, there is a small ravine (or indentation) in the grand plain, which on each hand is bordered by two
1835 Coquimbo — Terraces 181
300 [less] 120 = 180
little plains, of the same relative structure & scale as those in the city. — There can be no question but that their origin is contemporaneous. They are here covered with sand & loose shells, such as are found on the shores. —
About 3 miles within the valley the appearance of the parallel roads is best developed. — The main plain, although appearing so horizontal, has in a distance of about 2 miles Easterly risen 55 ft. being here 420 ft above Level of the sea. —
(V. Sect. II) I have drawn a transverse section to illustrate my description of the valley. (a) Beneath this plain, we only 43 ft lower we have V (E). — This probably corresponds to (E) in Sect: 1. — Although the relative height with the upper one is different. A rise in the main plain would necessarily take place, from the same cause, that the water shoals in entering proceeding up any bay, yet it does not follow, that when the its (the bay) figure was altered, that the slope of the bottom should continue uniform. hence the differences in heights of the same terraces in different parts of the valley may vary. —
This plain is of some extent. but is not present on the North side of the valley. — The terrace (C) is 180 ft lower (197 above sea) than (E). — Between these two on the North side, there are some patches of an intermediate one (Dn), which to seaward. becomes
(a) I have not attempted to give the proportionate breadths only heights. —
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amply developed. — Also on the North side the Terrace parallel with (C) has at its foot a small lower one (B n). — These to seaward the West unite in one cliff; but upwards expand into two fine, well cultivated plains. — These two lowest probably are the same, with those on which the city is built. —
We have then, beside the broard base of valley 5 distinct terraces; this agrees with the section (1) in front of the sea, that is if the supposed intervening one, is there allowed to be real. — As Capt Hall states, there are three which are generally most distinct, namely the two lowest (B C) & the grand one (E). —
(a)
We may therefore conclude the total elevation has of 360 ft has been raised by at least 5 distinct efforts, the force of which may be expressed by their mean height 72 ft. —
The main plain reaches about 10 miles up the valley: from the shape of the river being greater than that of its upper surface, it appears to fall in height. — Before the two would coincide the terrace gradually becoming narrower & more obscure, can only be distinguished by a few knobs on the hills sides & then is entirely lost.
(a) I must also observe, than in these terraces, beside their rise along the course of the valley, there is a most small slope towards the centre of the valley. That is the plain on each side if produced would meet at a very large angle. Again the terraces, which stretch across the mouth of the ravines, which enter the main valley on the sides, are sometimes slightly convex. Both these circumstances might well happen in a deep the bottom of an inlet or deep Bay. —
Hence it is manifest the same plain will differ in height, from the opposite & so called parallel one, if the points of measurement are not relatively in two direction in the same position. —
1835 Coquimbo. Terraces 183
The lower subordinate terraces, some distance lower down had disappeared. —
Guasco
The phenomenon of the Parallel roads is so much more strikingly seen at Guasco, than Coquimbo, that I will leave the regular order of my journey. The landscape there takes its its prevailing feature from these level & broard terraces. —
The distant Cordilleras seen through a long Vista offers in the intricacy of the a pleasing contrast to the formal & most singular foreground. Five plains are generally here as predominants, & attend the eye of a beholder as the three at Coquimbo.
The escarpements show the whole to be composed of shingle, which has sometimes parting seams of clay & is tolerably firmly aggregated (a). to at the mouth of the valley a low one is composed of a soft white sandstone, which is quarried. — on the surface of the lowest plains, there are lying many marine shells. — At Fregrina, 12 miles up the valley; the highest plain, is much more elevated than any at Coquimbo, & more extensive, to the North East it expands into a great Basin. — Five plains besides base of valley are here very distinct. 1 & 2 lowest are from 2-300 yrds.
(a) in the upper plain, the pebbles are white washed as in the plains of Patagonia. —
1835 Guasco Terraces 184
broard: the river is removing there. — the 3d is rather narrower — the 4th far broarder & the extent of the 5th or upper one has just been mentioned. — Between the 3d & 4th for space of a mile another terrace was distinct, but in no other part: Here then including the bottom of valley, there are 7 broard level steps, which it may be well believed, has a very remarkable appearance. — Their width of course vary varies much: one will expand, then dying away will leave a line of patches, till at last no eviden sign is left of its former presence.
The most striking instance which i saw of this, was where the 7 plains steps were visible, — the whole escarpements of all these for a short space were united, & showed one bold cliff. rising out of the bottom of the valley. —
The town of Belluar is said to be 25 [+] 12 [=] 37 miles above Fregrina: during my ride there, the clouds hung low & concealed the surrounding mountains. — The lower terraces had expanded into plains. — hence the view & structure of the valley. most strikingly resembled that of St Cruz. — who would have thought of going from Chili to Patagonia to find similar
[page partly excised at top] [These two microfilm images are out of order]
plain on the [excised]
there is here a peculiar configuration (a); having crossed over some extent of this one the highest plain, there is a low escarpement or cliff which faces to the North & at the foot of which is an extensive plain stretching many leagues to the North. When the sea occupied as a long winding inlet the valley of Guasco, this basin. must have formed a great lake or Bay probably connected to it by some outlet. —
Valleys
We must now retrace our steps & continue the description of the valleys to the North of Coquimbo.
Tertiary. In a small basin or cove distinct from the plain of that place, & and f a few miles distant, there is a small patch or Tertiary strata. They appear to belong to the intermediate strata, consisting of a yellowish arenaceous firmly cemented aggregate of broken shells of the Balanidae. — With
1835 Chili. Valleys 186
them. it was one Concholepas. (which was unexpected) & some fragments of silicified bone. —
At the head of the great Choros beach, there is a low. extensive desert plain, the surface of which is thickly strewed over with Bulimi & marine shells. — On the North. there is a line of low cliff. the plain to which it belong has over a covering, which reaches for several miles, of the Tosca rock. containing the same shells as at Coquimbo. — From here whole way to valley to Carisal. the country is level, low granitic hills rising like Islands. — in many places shells, at elevations which appeared to me seldom to exceed 200 ft. — Valley of Chañeral. we have the Tosca rock, with the Donax & Concholepas, &c. (perhaps higher elevation than at Coquimbo) overlying a coarse Losa containing many pebbles. Not mentioned in opening chapter
Beneath which come the hard, finely comminuted shelly mass of Balanidae, of a bright ockry yellow; there are a few pebbles & occasional layers of a fine aluminous. ockry or green. powdery stone. Tertiary
The whole section thus has the closest resemblance with that of Coquimbo. —
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The strata are inclined at a small angle to the SE. I believe the lower ones have not exactly same angle of dip, as the upper. — I here remain in doubt concerning the cause. — The Tosca rock is very abundant in these plains. I was forcibly put in mind of the similar appearances near B. Blanca — This substance is found further on at a considerable elevation & again near the valley of Guasco. —
Between Guasco & Copiapò I had no opportunity of exa seeing any of the greater valleys; as I followed a round near the Cordilleras. —
Copiapò
The mouth of the valley of Copiapò is bounded on the South side by line of escarpement of an extensive plain, which stretches some miles to the South along the coast. — One section gave for the upper stratum. grains of sand like shells, cemented by calcareous matter (Like Tosca & Losa mingled) in which are the Donax, pecten & Venus (2846) abundant. these overlies have elevation of nearly 300 ft. — they overlie variously coloured yellow or greenish. sand. containing few
1835 Copiapò — Valley. 188
round pebbles of granite & many of the large oyster. — There are seams of Gypsum. —
Another section gave for the lower strata a shelly aggregate; in parts abounding with layers of soft white & reddish rotten stone (Tripoli) 2847. 2847 —
With these were very numerous seams of Gypsum generally horizontal. — Amongst these fine sediments there were blocks of Granite, one of irregular shape had mean dimensions of 6 x 3 x 4 ft. How are such transported over such short distances?
The strata are superimposed on the solid Granite formation. — Near the coast where the cliff is much lower, the upper part consist of shingle, which like the Tosca contains the recent shells as Venus Pecten, [Olina] &c. — A similar formation, said to abound with the oysters must exist at English Harbor. [blank] miles to the North.
the above plain, which forms an escarpement on the South side is not continued to any but a short distance within the valley of the river. — Some leagues up however, on the sides, a small narrow step has been cut out of the solid rocks & smoothed over with shingle. — In several parts of the
1835 Copiapò — Valley 189
level & broard bottom of the valley; there are extensive superficial layers of saline matter. — These are white & encrust the ground in a crumbling state to the depth of some inches. — By analysis at Apothecarys Hall, consist chiefly of Carb: & Sulph. of Losa. — Their origin is to me quite inexplicable. — The same fact occurs on a lesser scale at Guasco. (a)
Near the town of Copiapò, the valley expands into a plain, here & for a short space higher up, the scale & appearance is like the Valley of Quillota. — Above the town the valley bends in a very southerly course, which is different from the common order of things & its length is from the same reason great. — It is remarkable by its the bottom having a more ordinary alluvial covering, & not as in the other plain valleys pure shingle, I do not know the cause; perhaps its inclination is less. —
Near the mouth of the Valley of the Despoblado, which joins the valley of the river a short distance above the Villa, there are two considerable plains. which have these escarpements [sketch] above each other & arise from the level of the Valley. With
(a) In the hills in this part of the valley there is a curious appearance: Hills are coated with loose sand, to an height from 1 to 200 ft. — It appears simply blown up & as on hillocks near the coast; it is, the far greater height & distance from the sea than usual, which causes this singularity. — There are here no remarkably strong prevalent winds to cause it. — The very same fact is very conspicuous at Iquique in Peru & I believe commonly on that coast. — Do winds in all parts of the world imperceptibly carry inshore dry sand? whilst its accumulation is prevented by the removing action of rains? Does not a similar occurrence take place in the deserts of Africa & other dry countries? If so the land near the sea coast would must gradually rise & become coated with sand & fine earth. — In North Wales I have been told, during gales. the sand is frequently blown with by the wind several miles within the mountains. — In such a climate however it cannot accumulate on the sides of the hills so as to be conspicuous. —
1835 Copiapò. Valley 190
this exception step-like terraces are not found in this valley. — I must however call to mind the elevated plain of gravel & horizontal tufaceous deposition. which cap the mountains nearer to the Cordilleras. —
Valleys
The desert valley of the Despoblado is in its dimensions of the first class: although its sources lay in the main ranges, it is quite dry. — Its base, which is broard & level, is not only furrowed with the a mere gutter. — is composed of shingle. — Higher up its is quite smooth. — I saw one large side valley, with a bar of earth 30 ft high, (formed I do not know by what accident) stretching right across the mouth, which was narrow. — From this source no water could for a long period have entered the main line. — The crumbling sides of the huge mountains. have their ravine filled with loose detritus. as the The whole aspect. is that of permanent tranquility; this in mountain scenery is of such unexpected occurrence that it strikes the beholder with surprise. The cause of this extreme dryness of the
1835 Copiapò — Valley 191
climate. The valleys in other respects have an ordinary appearance, yet at no time, from the smooth outline of the bottom. can it have acted as a drain of any size. — I feel no doubt, that its present form is the same which was impressed on it during the gradual retreat of the ocean (a). — I may mention. that high up (near junction of Quetrada of Maricongo & Arufa) there is on one side a step formed plain. — neither must the tufaceous formation be forgotten. —
I have now drawn drawn a sketch of all the principal & far greater number of the smaller valleys. in the interval between Copiapò & Valparaiso. At (P. 49) the same thing is done to the South of the latter place to it as far as the R. Rapel. — From the description of the valleys in this line of coast, an extent of about 400 miles, the following conclusions appear to me inevitable. —
That the sea, during a long & quiet residence deposited these masses of shingle stratified with seams of sand & clay, (b) which in Europe would be called Diluvian. That during this time it must have modelled the surface of the higher land, which surrounds the plains
(a) The evidence of which is found at its mouth, in the terrace-like plains. —
(B) The residence of the sea. explains the general occurrence of Porph. Breccia above the Granitic formation in an abrupt escarpement, which fronts the sea coast. — We can only suppose. that the thin edges have of the strata have been worn away. where the Pacifick stood at a higher level. —
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Basins & Valleys. — That in its retreat has frequently extended these deposits into step-formed terraces, which rise one above the other by step-formed escarpements. valleys
That even many of the minor inequalities, (such as lateral ravines) formed by the sea, are still preserved. — That the rivers flow in the troughs of the former inlets or creeks (a); that their action is confined to the bottom & lower terraces, which they are tending to remove. —
That the step-formed terraces denote epochs in the progressive rise of the land. — That from 200-300 ft of this rise has taken place in the whole line of coast, within the period of existence of present shells. — That in this ascertained fraction there is no difference, there is no difference in the outline & appearance of the land from what is found at much greater elevations. —
Having drawn these conclusions from a tolerably minute examination of a large country, one feels tempted to generalize fr them perhaps beyond what agrees with truth. — (at P 54. there are some former conclu results
(a) this law being supported by the evidence of every valley, without exception in northern & central Chili. — that their action &c &c
(B) now strengthened by the above description of to which I will then add a few words.) —