RECORD: Darwin, C. R. Geological diary: S. Cruz. (4-5.1834) CUL-DAR34.131-150 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, corrections by Gordon Chancellor 4.2011. RN2

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Marginal notes are here integrated into the text.

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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.


131

1834. April May S. Cruz (1)

6/353/5

The plain South of the anchorage is 350 355 feet high; it forms a praecipitous cliff. The lower 1/5th or 1/6th of this is a more or less hard, pale blackish, muddy. sandy clay; it contains very many shells, irregularly placed & many broken. —

p. 15 dimensions of river

In some places the large Ostrea is abundant in layers, generally Turritellae, Arcae & Venus are very common. — There was one Voluta, which I believe is the same as now is living in the sea. — 1946 ... ... 1968 1972; 73 Of the Pectens, Scutellae, & Balanidae, which are so abundant at P. S. Julian. I saw none. — The shells in some cases are silicified, in others converted into yellow crystallized calcareous spar. — The upper part of cliff is essentially composed of a soft. yellowish, earthy sandstone, more or less laminated & marked with ferruginous lines:

This great mass may often time divided into three divisions, the upper & lower are similar; the sandstone here is considerably laminated with an irregular inclined cleavage 1969; there are also horizontal lines of stratification; this substance (a) but rarely contains any shells (1967. an exception). —

— there are present some few hard. calcareous compact concretions. 1970 — it is much interlaced with veins of crystallized gypsum, these are generally thin: the gypsum very sometimes does not quite fill up the vein: The Gypsum seems to crystallize transversely & from each side the lines. when not long enough to reach across are bent, this [sketch]: — In a large extent of cliff I found in the veins of gypsum a considerable quantity of a white salt; it also occurs in crests & veins by itself; it is always found

131 verso

(a) There are however layers of large oysters & other shells. above this sandstone as well as below it. —

(b) There is a strong exception to this in the presence of the curious large few (5?) ribbed Pecten of the North

All the heights when not specified to the country apply to the river

The subsided masses in valley of S. Cruz parallel case to great slip in static series of southern England. see Conybeare & Phill: — I do not understand theory. read about Isle of Wright —1

Lyell has compared Icelandic streams to England. p. 374 Vol. Edit. Volume?2

1 Conybeare and Phillips 1822.

2 Lyell 1830-3, vol. 1, p. 374.

132

1834 April. May S. Cruz (2)

in a highly uncompressed form, sometimes generally quite white & pure. (946 tin label) — There were a very few shells close beneath this gypsum & salt. — It is a very curious fact that how a soluble saline substance should be present in beds deposited by water. — The central division only differs from these two in being more compact & in containing several horizontal lines of great concretionary masses of hard calcareous - sandstone. 1971 —

They contain many shells more generally venuses. — are coloured externally fiesty red; are sphaerical or more commonly much flattened. (a) They sometimes join so as to form a necklace. — These globular masses have a concentric structure, are even 3 & 4 feet in diameter, in the same line they are often two & three yards apart. — Their presence is clearly to be attributed to calcareous matter, having at intervals been deposited & so caused a chemical attraction between the particles. —

This attraction must have acted through a space of 4 feet by 9. [sketch] 4 9 : — The layers or lines of balls might be traced for many hundred yards. —

In some places instead of the foregoing beds, we have a loosely aggregated sand such as specimen (1993). —

I was much struck by the great mineralogical resemblance of the yellow sandstone beds & its concretionary masses of calc. sandstone with those on the East coast of T. del Fuego. — The gypsum & extinct shells, however at once point the difference perhaps this resemblance is owing to relative

132 verso

(a) [sketch] A B C

(A) common form: (B) where many of these have united forming a sort of necklace — (c) not an uncommon form, where a thin bed or layer of hard sandstone is almost completed. —

Does the white aluminous matter contain magnesia? —

Study Sedgwick on Concretions in Magnesia limestone1

[sketch] qH 2 0 2 qH

1 Sedgwick 1835.

133

1834 April-May. S. Cruz (3)

proximity to mountains of the same class. —

The lowest bed & its organic remains closely resemble those at the S. Barranca of Port Desire: the upper beds differ from that remarkable similarity in nature, which extends from P. St. Julian to the Peninsula of San Joseph. — We shall presently see, that in ascending the river, white, aluminous strata of the same character with the ones alluded to pass insensibly into such as occur at these cliffs.

Above all the above beds there is of course the usual one of pebbles; these are as before almost entirely porphyries, perhaps paler coloured ones are more frequent:

The St Julian yellow one is common 1996 & 7, but not quite so abundant as these to the North; some of these were the size of 1/2 a mans hand; generally the pebbles vary from very small to hens-egg: Gr. there is a marked change in the presence of a considerable number of compact, black slate ones. — the pebbles are often white-washed with aluminous matter. — The gravel fills up inequalities in the lower beds, hence vary's in thickness from 20 to 35 (about) feet: it is covered by a bed of earthy sand from 2 to 12 feet thick which on the surface of which (350 ft plain) are lying striated Mytili 2001: Buccinunes, Patellae, & fragments of a large Voluta, now common on the coast. — some of these latter were found some miles inland, at an elevation of about 400 feet above the sea. —

The general features of the country are

133 verso [blank]

134

1834 April-May. S. Cruz (4)

the same as to the North. — The facts noticed in this neighbourhead about the elevations of the country &c &c. (a) will be mentioned in connection with others of same nature, observed during the expedition up the river. —

I will not mention what I then saw of the geology of the interior country. —

April 24th [1834] — From Up to 50 [illeg] miles in a West line up the river, to from the coast, the universal stone is is the yellowish clayey laminated soft sandstone, (as near the anchorage it contained in places many Ostreae-Turritellae & Arcae &c — The mass of cliff was here first very perceptibly banded with whites varieties, but a gradation might be traced, till it quite died away as near on the coast. A few miles further (2d series) on we have cliffs 416 feet high;

?? 558 ft. above sea

25th — the upper part gravel. partly cemented together by aluminous matter, beneath which there is a loosely agglutinated sand. (like 1993) 67a.59b exactly 60 miles; they are traversed by greenish yellowish, whitish, more aluminous bands. — I saw no shells. — they contain large balls of hard calcareous sandstone. —

Lava

In Long. 70°.2'. (67 miles from W of mouth of river) we first met with a very interesting feature in the geology of the country in the presence of a great field of basaltic lava. —

The course of the river seems here to be partly determined by the southern points of the stream of lava; higher up it cuts through it: Hence on the South we have the usual formation; on the north shore, alternately p simple cliffs & others capped with lava (b). — V other side of page

134 verso

(a) I need only state that behind the 350 plain there is an escarpement, running across the country 840 ft, clearly of the same general, formation. I saw base specks on the sides of the hills, but not sections. —

[sketch] Great Patagonian formation. — Plain
(b) (x) River Lava
main lava field 381 ft
419 plain over lava
lava: higher than the 278 ft
plain as (x)
lava 381 936? sea
(x) 418 ft plain 538 above sea
lava river

[calculation] 212 [+] 322 [=] 534

[calculation] 530 [-] 130 [=] 400 lower surface of lava

[calculation] 1264 [-] 534 [=] 680 down sea [-] 400 [=] 280

[calculation] 1416 [-] 534 [=] 882 [-] 400 [=] 482

[calculation] 1416 [-] 212 [=] 1204 [-] 530 [=] 674 [-] 482 [=] 192 [+] 130 [=] 322

[calculation] 130 [x] 2 [=] 260 [+] 65 [=] 325

135

1834 April-May. R of S. Cruz (5)

[calculation] 381 [-] 275 [=] 103

The surface of the lava forms a plain, which is only a little less level than the usual ones. —

530 ft above sea

its altitude is here 381. feet above the river: some springs 262 above river would lead one to suppose the thickness to be 117 feet. — but as I found a edge of cliff 278 feet to & which at least must have been 20 to 30 feet thick. — I imagine that from 120 to 140 will include the lav whole depth of the lava in this extreme part of its stream. —

[calculation] 530 [-] 381 [=] 159 540

The lava is black or angitic, contains often-times small crystals of olivine 1980: 81: 1982:: is more or less cellular: when in the former state is very tough & higher up contains much amygdaloidal (zeolite?); when in the latter is sonorous more brittle, & divided into columns. — The crevices between the hexagonal columns is in some places filled up. by a white friable calcareous matter. 1983 — The upper & lower surfaces of the lava are of course much most vesicular; the upper surface has often-times a laminated. concentric structure. forming an aggregation of great balls. — From all these appearances alone (most striking resemblance with P. Praya lava) there can be no doubt this has been a submarine stream. —

On the face of the cliff, there was a line which extended horizontally for the whole length.

this was seen by the lava not only being vesicular but even smally cavernous. the roughest part rested on the great balls, such as we have seen on the surface of the plain; above the line the lava was columnar. — I think it is certain this line marks two distinct flows; there was another obscure, about which I could not feel sure

[sketch in margin]

135 verso

(a) The globular lava passes into the hexagonal columns. — The columns. are generally small; but in one place, (further up the river) I saw some pretty regular hexagons, whose sides, could not have been much less than 12 feet each way. —

136

1834 April-May. S. Cruz (6)

I was interested by tracing any rent from either the upper or lower surfaces of the stream & seeing how invariably on both sides the rock was vesicular: this evidently must be owing to water penetrating & from the heat generating steam. — lesser pressure

The fact of the body of lava not being poured out at one period explains, an appearance of steps & small plains of lava of different heights, which may be noticed in some of the extreme points, where they stand denuded from the envelope of the softer beds which before the formation of the valley covered them. —

I never saw a contact of the lava with the lower beds, but frequently at a little distance below it. — They were of the same general nature, as all the others & will t subsequently be described. —

I should have noticed that all the cliffs & plains, are bounded by another & higher series, at their back & these evidently are of the same general formation. — I could see the lava running directly to their base & I have not the slightest doubt running under them: to explain my reasons for thinking this, I must shortly explain the structure of the great valley. —

[sketch] (B A first valley 2d valley D A B

It is bounded by ranges of elevated (B) cliffs. 8 or 10 miles apart; the river flows in a much narrower valley (D) bounded by 2.5 miles (AA) the cliffs of lava or azotic form: I at one time thought that the lava had perhaps followed the first valley ([illeg]) & therefore did not extend under (BB) & was not contemporaneous with the great oyster formation. — but this is not the case

136 verso [blank]

[page] 137

1834 April-May. S. Cruz (7)

for if so (BB) must have been above the water, in order to form the valley; now higher up the river, we shall find lava at a height corresponding to this series of plains showing equally that it was formed under the water; in the same places we see the lava descending from the Andes on the N & S side of the great valley, if the first valley, & of equal height on each side, this valley then must have been quite fill, & would have been the last place to be penetrated re-cut. —

I might have spared all these reasons

the stream has moreover the appearance of coming from a little to the northward & not down the valley: but chiefly if this valley had existed, gravel would have underlain the lava. — Another reason proves that the lava was poured out during the deposition of gr. oyster formation. —

it this that in an imaginary section of extremities of the stream (as seen back of p. 4) we have it thus: [sketch] (the headlands are brought close together); the horizontal lines are oyster formation & inclined by lava. — if the lava had flowed after the excavation of the first valley the intervals between its extremities would have been filled up with gravel & not with part of the oyster formation. which certainly is not the case. for it is as represented. —

We During then, the deposition of the oyster formation a great stream of lava was poured over the bottom of the ocean, the depositions

137 verso

calculate — size of bottom, subtracting the thickness of base from upper & lower

[calculation] 84 [-] 67 [=] 17

[calculation] 525 [-] 381 [=] 144 [+] 45 [=] 199 (200)

[sketch]

138

1834 April-May. S. Cruz (8)

continued to take place: the universal covering of porphyry gravel was spread over this. & then (probably at f owing to an elevation &c &c) the "first valley' was excavated, & recovered recoated by the gravel from the upper series of plains. —

the depth of the excavation would be very much determined by meeting with the hard surface of lava. — hence the equality of height in the headlands, where this stone is or is not at present. V Diagram Section — in some cases the lava is quite base, in others is covered by thin bed, perhaps chiefly, of gravel, which makes its height correspond with the plains

G} (AA) — one little patch thus lying on the lava was 65 feet thick. —

I have stated that the lava, about when first met with is 381 ft. above the river, in the next 15 miles (a) we first have it 414, & then 525 feet. —

April 28th

this rise is fo chiefly to be attributed to the thickening of the lava, but also to a rise in the bed on which it is incumbent.

84 miles W of mouth of R.

At this latter spot, there was a plain, or headland without lava of exactly the same height with a field of it; it appears to have been the spot, where the stream separated & diverged, one continuing along the north side of river, the other crossing. directly to the South, across the valley. forming a small plain, which run is soon lost beneath the higher plains of the oyster formation. —

To the North the lava rises in several steps (owing probably to the cause previously explained)

138 verso

(a) & within 3 or 4 miles of the 525 plain, there are irregular plain of hillocks of lava 740 ft above river. giving a sudden increase of 212 feet probably owing to a second great current. — this I see is mentioned twice

As the angle of inclination of the river is probably very nearly that of the bottom of the former ocean this daily increase of height of lava expresses the increasing thickness in bed. which in 14 1/2 miles was 144 feet giving an angle of 5°'' 31": perhaps 1/2 of this angle is due to inclination of surface covered, I say half because I observe believe this is proportion of rise between the plains without lava & those with it.

Near the Andes the lava thickens at a much greater rate, owing probably to a succession of streams. — One angular measurement on North Sea of basin would make it 3300 ft above sea

[calculation] 1416 [-] 212 [=] 1204 [-] 530 [=] 674

[calculation] 1416 [-] 530 [=]

[calculation] 322 [-] 130 [=] 292

[calculation] 100 [-] 67 [=] 33

[calculation] 740 [-] 525 [=] 215

139

1834 April-May. S. Cruz (9)

& likewise appear to run directly beneath the higher range of escarpements. (such as B) — A few miles from this spot the lava looses much of the regularity of its upper surface; the 525 rises with a very gentle inclination & rounded outline of shingle to the height of 740; here there is a tract of land with irregular masses of vesicular lava protruding through the porphy: gravel. —
[there is writing in the margin next to this paragraph, largely illeg] about W of [with]

I attribute this to to the diverging & crossing of streams of lava; but the whole is so smoothed over with gravel, that it is difficult to be made out. — [word crossed out in margin] In the next 20 miles the lava plains continue to rise, at about half way 7 miles (a). I conjectured the plain to be 800 feet; it here also crosses the valley of the river & is seen but to no great extent in the south shore. — 94 ? miles

April 29th

The lava is here of rather a different mineralogical nature perhaps not quite so cellular, but much more amygdaloid 1984: ... 1986 (I met with some before) with white crystals;

there were other varieties further on 1987 to ... 1989; some black compact, other grey, stony & laminated. — The specimens show a good series, (1981. 1980 & 1986) perhaps the commonest varieties. — The end of the 20 miles was the last spot I measured the lava. V. paper (about 100 miles from mouth of river) the lava was 910 feet above the river upper surface cellular; judging from line of springs 212/422 & places where I could see the inferior beds, its thickness must have at least 323 feet: this is covered by a great mass 212 feet (making total height 1122 ft) of porphy. pebbles 1416 ft above sea (probably in the lower parts chiefly) &

139 verso

(a) The plain was very irregular, having expressions & inequalities in many parts. — Some of these were the result of original forms. — In a gorge, I observed the following appearance;

[sketch] 1. 2. 3. 4. 5.

The uppermost part of one side was composed of 7 or 8 separate distinct arches, showing towards the gorge a section. — they were about 20 feet high, & broard as represented, but further part; being separated by little valleys: From if these were very distinct. — there were some lines concentric with the exterior surface & the mass divided into irregular columns. which all pointed from the centre of the arch. — 3. appeared like two joined. & 5. was narrower & higher than the rest. —

I believe lava is always columnar in lines at right angles to the cooling surface (seen in dykes &c); hence the lava, when soft, from some check in its course, or other cause, must have been thrown up into these wave-like ridges, the section of which is seen by the gorge; if it had not been for the spoke-like columns, it would not have been possible to have been certain that these were original forms & not resulting merely from degradation. — These waves also occur in a part rather lower than the rest of plain. —

N.B. It will bear questioning whether this is of concretionary origin or as described. — I believe in latter

140

1834 April-May. S. Cruz (10)

enormous angular blocks of lava (a) & the feldspathic slates of the Andes. — It is probable, that this elevated mass of lava was never covered by the oyster: form: beds. — or if so they have been removed. —

there is not therefore any range of island, higher escarpements. — I should have observed that the mass of alluvium forms a plain, but not very regular & has the appearance of being formed beneath water; which in itself is far most probable as a means for transporting the enormous blocks. —

May 1st

The valley here widened considerably, & I never was able to reach the lava; I could see it on the north side, gradually rising in a broken, irregular plain, to very near the snowy cones of the Andes: it was much traversed by large valleys:

a crater for such deluges probably large

in several places, beneath the white beds horizontally striped might be seen. — On the south side the lava is not nearly so abundant, but yet in the distance, towards the west, its broken outline, rose towards the mountains.

I feel no doubt that it has flowed from the same one of the lofty mountain, which we be beheld stretching along the country in a N & S line. —

This lava being proved contemporaneous with the great oyster form: (in which several extinct shells are found) is important, in as much as it shows that the Andes even at that period was a volcanic chain. — I believe the most be southern volcano, now known to be active is between 400 & 500 miles to the north of

140 verso

(a) very little rounded such as a rock appears in situ. —

Z

I see Feb. 1841 —

170 miles in st line from range of lofty mountains to coast. —

141

1834 April-May. S. Cruz (11)

this field of lava. (a) — Its extent corresponds to the greatness of all the formations in S. America. — Its extreme limits are nearly less than 100 miles (b) from the nearest range of lofty mountains & its thickness. there, is from 100 to 140 feet. i.e. in space of 46 miles — At 60 miles from the same source it is 323 feet thick. —

To return to the oyster formation, I have noticed that the cliffs gradually became more & more banded with different colors. — at about 80 miles from the mouth, there were beds of a quite white, aluminous substance, such as (1992) & others of a greenish color as (1999) (1990). — Soft agglutinated. coarse of sand, already mentioned was also abundant; it contains sufficient aluminous matter to cake with water. —

Before this I saw some small layers of hard, ferruginous sandstone, & in one place in pale clayey sand, containing concretion of "tosca rock" marked with manganese precisely the same as occurs in the Pampas.

April 28th

At this place the strata. presented a curiously deceptive appearance; the cliffs of the plain were half a mile inland of the river, on the margin of the latter, there was a number of hills 60 or 70 feet high,
note
where I found all the strata dipping at high angles: generally at 45° to the cliff, some vertical, others dipping towards the river. — this was seen for an extent of 3/4th of a mile; I at first thought that for the first time in Patagonia I had found strata bearing witness of disturbance from below: on examination I felt convinced, that it was owing to an enormous slip.

141 verso

In England we should hesitate in attributing any step of trap rock in the counties of Nottinghamshire or Leicestershire to the highest mountains in Wales; yet the distance is not greater. —

I was struck with the general resemblance of this volcanic formation with that of P. Praya; in the same manner in T. del F. I was surprised with the similarity of the Hypogene & metamorphic rocks of Lyell with those of Europe; it appears to me that this general similarity over the world alone is a presumption in favor of some hypothesis which attributes volcanic. trappean. hypogene & metamorphic rocks to the same creating or altering cause: —

(b) This is probably too little as the nearest mountains which are the least apparent probable ones. —

142

1834 April-May. S. Cruz (12)

all the above beds where not capped by lava, was covered with the usual bed of shingle. —

At a th little more than 100 miles from the mouth was (& about the middle of the continent), there was a very good section: the softer beds have an altitude of 587 feet, where they are covered with lava; the lower part, for about 250 ft is hidden by a tubes, of the what is seen this is a section. —

[sketch]

1 /
2 brown aluminous sandstone
3 white. aluminous. 1992
4  
5 green alum: 1990
6  
7 3 layers of white & brown, indistinct
8  
9  
10  
11 ferruginous sandstone
12 2 white & green, indistinct
13  
14  
15 mass of soft sandstone containing very small pebbles
   
  Talus

There were many other alternations, but these represent the most distinct ones. — The Brown Alum: (1 & 4 & 6 &c) sandstone varies in character from (1969: 1992 & 1993). The white aluminous bed 1992 is very striking from its color: in its nature it would seem pretty closely to agree with the beds found at P. St Julian & Desire invariably underlying the oys beds with shells. There is however this marked difference that here the supplies appear to have been intermitted but there one a constant one. — Perhaps its source [illeg] to the North. — Approaching the coast, we only see vestiges of it by white lines. (a) —

The green alum: 1990 only differs from the Brown in its color & perhaps rather more aluminous nature: seen in the cliff the color is very observable. — The lowest bed, would appear from what I could see, to be of considerable thickness, it is an indurated coarse sand, almost made up of very small pebbles. (1 or 2. 1.10th of inch long) of blackish clay & feldspathic

142 verso

(a) A person not tracing the beds from the anchorage to this place, would perceive little identity in the two sets of strata; on the other hand generally. on the coast of Patagonia, the mineralo[gical] cal. character is constant even in the minutest particulars. I think this is what might be universally expected. viz. that the greatest variations would be found in the line to the original source of the depositions. —

The plain at section is as much more above level of sea, as river is. —

212
323
577
250

212
323
587
1122
250
1370

1400
1120
280

143

1834 April-May. S. Cruz (13)

Similar beds will presently be noticed. —

Such variations as the above do not remain constant in order for a mile together. — There were no shells, but in the neighbourhead some of the large oysters were seen. — Occasionally there were large sphaerical masses of the concretionary calc. sandstone. —

To finish with the cliffs. —

[sketch]

1416 above sea level angular blocks & gravel 212 ft thick
lava 323 ft
587 ft high, various alternations as above
sandstone with pebbles
 
River of S. Cruz

Above the lava 320 ft there is a great mass 212 ft thick of porphyry pebbles
size [illeg]
& great angular blocks of lava clay slate. feldspathic rock & chloritic slate (G) — these were commonly from one to two yards square, & even three. — From the difference shape, size, & nature from the porphyry pebbles; from these being first found scattered over the gravel a few miles to the westward, I think it probable that their date is distinct & posterior to the porph. pebbles, probably some sudden convulsion connected with the upheaval of the country.

[calculation] 212 [+] 323 [+] 587 [=] 1122

Risen here say 290 ft July /44/

These blocks are of interest, as doubtless showing the prevailing rocks of the Andes in this latitude.

Clay slate (a), & especially feldspathic do (sometimes porphyretic with feldspar) 1994; & a chloritic ? slate with much quartz veins are the commonest. 1994 1995 —

The first block of these such rocks, which I saw, was about 67 miles from the nearest range of the Cordilleras. —
[illeg] (no)
About 6 miles West of the above cliffs there is a plain in the great valley 310 ft high. —
[illeg] river
I found part of this composed of a yellowish sandy earth, alternating with & containing beds of pebbles; these varied in size

143 verso

(a) I saw one only of true granite: its dimensions were 5 ft by 3 & 2 deep an oblong: there were others, & smaller ones of imperfect granites but not common, I saw a few of an ancient looking conglomerate:

Some of the blocks belonging to this bed were immense; one was a square. of which each side was five yards & height above ground 5 feet & probably twice as much beneath; it was angular: another of the same feldspathic rock was rounded, about 60 feet in circumference & 6 feet out of the ground: there were endless numbers of two, three, & four feet square. — generally but little rounded. They are at present at least 55 miles from their original site. — What a vast tumult in the waters must have carried them this far; their shapes preclude the idea of rolling by degrees along the bottom of the ocean. —

The 5 yd square one is so little rounded, that for some time moments I thought it was a point of the solid rock protruding upwards. — even with my compass took the direction of its imperfect cleavage & of signs of being rolled — [there is evidence of a sentence underneath the present text] [illeg]

Glaciers & floating Icebergs have frequently been brought forward as the means of transportal. Capt King in his paper in the Geographical Transactions has this remarkable passage "It was named Sir G. Eyre's Sound. An extensive glacier sloping into the sea. from the summit of a range of high mountains, that are visible from many parts of the Mesier Channels, terminates this sound; and near the head of it several large Icebergs containing no inconsiderable blocks of granite were found aground." This is 6 80 miles to the North of the head of S. Cruz river & in latitude 49°. —

144

1834 April-May. S. Cruz (14)

from a walnut to an apple & occasionally to twice the size of a mans fist. — they were well, rounded, & composed of clay & feldspathic slates & pale-colored porphyries, (a) precisely similar to the great blocks & to the lowest bed of minute shingle. — It was very All having clearly proceeded from the same source. —

G It was very curious to observe that on the most careful examination, there was not a pebble of lava, & what is still more so, none of the "St Julian yellow" or the red sorts of porphyries, which compose the covering of the whole of Patagonia. I before conjectured that the source of the pebbles & blocks at the former section were distinct. —

With the pebbles there were some of the large oysters, some of these were rounded, they probably owed their presence to the same currents which brought the pebbles. — I may here notice, that a few miles further up the river I saw a pebble of calc: sandstone with Turritellae, as at the anchorage, this proves such beds exist here. — Also, that in many places there were groups of fragments of petrified wood, lying on the surface. — I never found any in situ, but there cannot be much doubt? 1975 ... 1979 that they belong to the great oyster formation: — some of the specimens appear curious. —

The furthest point West to which we reached was 135 from the mouth of river, & we were then 20 miles from the nearest range of the Cordilleras: in the last 20 miles I only obtained sections near the river. — the universal stone is a soft yellow, much laminated aluminous sandstone 1191; it contained

144 verso

(a) This fact is important, in as much it renders it almost certain, that a chain of terrestrial or submarine hills existed (containing porphyries) previous to the deposition of the greater oyster formation (& included lava) & to its elevation. —

145

1834 April-May. S. Cruz (15)

here & there a pebble of the rocks last mentioned but regular beds of such pebbles were very rare. — This clayey sandstone in some places contained darker, argillaceous beds, in others hard concretions of calc: sandstone. — the horizontal beds were often divided by a highly-inclined, curvilinear cleavage, manifesting by its forms the action of currents. — G These lower plains were covered by a thick bed of the common shingle. —

At the furthest point, on the banks of the river, a Patella was picked up. — I should have not have noticed this, if 30 miles further down I had not seen another & two broken Volutas 1974; the same species which now exist in the sea, the taller partially retaining its color. — These shells probably come from a basin at the head of the valley, which appears to have been the bottom of an inland sea, its altitude above the sea is about 440 feet. — : the river here itself is 410 ft & plain about 30 ft above this

Boulders

The river of S. Cruz. winds from side to side in a broard straight valley: its depth in centre about 17 feet. & width varying from 200 to 300 yards; its stream runs constantly from 5 to 6 knots, it is very remarkable in having no still reaches, or lakes; its bottom appears to be all shingle: it is subject but to inconsiderable freshes. — What power has such a river in transporting stones? —

G The lava first occurs about 67 mils from the mouth of the river; in the first 20 or 30 miles I in vain looked for the smallest fragment; after this they very slowly, but gradually increased; the lava was always of the most cellular kind

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Boulders

& hence not well rounded, they were small & till many miles further up. None were the size of a mans head (؟ one block an exception??); they were no where numerous untill when about 5 or 6 miles in the NW, I saw the angular outline of the lava; here the blocks suddenly became very numerous & large, & as soon as we reached the cliff the stream was bubbling amongst a pile of blocks huge fragments. — Till one hour before I saw the field of lava, there was nothing in the bed of the river, (although carefully at the time examining it, from the first, having thought it would long foretell any change, which led me even to conjecture that concerning its presence.

Considering the rapidity of the stream, which is such that no boat can pull against it. I was very much surprised at the above facts; & the more so, when afterwards it was seen, that the field had once stretched across the valley. This great mass however was removed, when the sea formed a strait in this valley; & the fragments, perhaps have chiefly been washed into the ocean, & partly buried in the covering of the lower series of plains

For the next 28 miles the river course & sides was strewed with blocks: after this many feldpathic & chloritic rocks was mingled with them; in a very short space, owing to the valley widening & its sides of lava becoming further apart, the lava blocks rapidly diminished in numbers, till at the spot, we last reached, there were absolutely none. — The feldspathic blocks ones were more than in proportion numerous; many of them, of great size; they are entirely due to the great mass of alluvium, already described

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1834 April-May. S. Cruz (17)

which covers the upper as well as the lower series of plains. — As in the case of the lava, to the W East of the place mentioned (which is where the blocks are first found on the high plains) I saw none one of them of the feldspathic ones. — Or rather there is one solitary exception, 35 miles from the mouth & 60 below where such blocks are common, there was one feldspathic one (a): it was rounded 7 feet in circumference, & 18 inches striking out of the muddy gravel. —

I have said, that where the valley is wide, high up, the lava blocks cease to be present; yet both on the N & S shore, at 6 or 7 miles distance the cliff of lava might be seen trending towards the mountains, & the river, by many of its branches must again pass the sold rock. —

This part of proof I do not think very strong, only presumptive

These statements prove how little power, a very rapid stream (even a little assisted by freshes), has to move any large stone down an inclined plane such as the bed of a river. —

Gravel

I have described the gravel on the plains near the anchorage; in ascending the river, on its character gradually alters, till at our furthest point there was but little resemblance. — The red. & "St Julian yellow" porph: are almost lost & in their place are clay slate, feldspathic & white porphyries; excepting from the latter; I could scarcely have distinguished the bed of this river from one in Tierra del Fuego. — This, I think, is chiefly to be attributed to the river cutting through, beds containing such pebbles rather than to the river having its sources in the mountains composed of such rocks. —

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(a) As this block is so truly a solitary exception, I think some extra-ordinary cause must have given it its present position, such as during a hard winter, being imbedded in ice & thus floated down. —

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1834 April-May. S. Cruz (18)

Gravel

There are many points of high interest connected with the bed of shingle, which covers the whole of Patagonia. — In extent I should think it would equal any in the world; detached masses pebbles are found from N. of the Colorado to about Staten Land, a distance of more than 1000 miles; from in breadth from the foot of the Andes to the Falklands Isd between 5 & 600 miles: the continuous bed extends from the same place to the R. Gallegos. 7-800 miles, & in breadth I think, as at S. Cruz, it must always extend across the continent to its source, the Andes. —

[sketch] 400 750 150

This bed varys in thickness at coast from 20 to 40 or 50 feet, & is entirely composed of pebbles. (a) — When we consider the immense bulk of this bed, we must add to it. the mud produced by the attrition of the stones, which would I should think at least be equal to the gravel. — argument for slowness

We may well wonder how any chain of mountains could supply such a mass (& this only on one side) & yet retain their present lofty elevation; it is instructive to consider, how much gradual wear & tear has removed of solid rocks. — How immense they were forming on the eastern beach of the Andes. — I should think long anterior to the deposition of the first bed of the oyster formation; indeed perhaps these very beds partly result from the sediment caused by the attrition of such rocks:

It is however remarkable that in no one part of this formation do we find these pebbles, yet on every part (whether previous or posterior to successive degra denudations) they abound. —

We have seen, that the pebbles on the plains

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(a) High up the river it is 212. — So that taking a mean of 50 ft for whole plain, would in fact be understating it. The decrease of thickness in gravel, mus near the coast must be partly owing to its having redeposited more than once & hence undergone attrition the same same number times; the mud, which is produced being carried away.

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Gravel

at the anchorage are not the entirely derived from the prevailing rocks of the Andes in that latitude; nor do they come from the neighbourhead of T. del Fuego, judging as well from straggling blocks as well as from what I have actually examined in that country. — They without doubt, come from a somewhat northward part of the Andes. —

It is very difficult to conjecture, what could have caused this SE stream of pebbles, which had long been accumulating at the base of the mountains; it took place anterior to the first elevation, which raised Patagonia into dry land: but probably is intimately connected with such phenomena. — It seems to have had (as might have been expected) a decided effect on the zoology living beings of these seas. —

A sudden change in the nature of the bottom, must destroy many animals, & when of great extent, if the species are not in proportion more extended, they must perish from the world. — The superior, white aluminous beds with gypsum perhaps have had an equal or greater share in this work of destruction. —

NB. Perhaps the pebbles were forming & being scattered abroard during a long period of time (a) after deposition of last layer of oyster formation: we by this supposition make it still more extraordinary that for a space of many ages, not a pebble was transported, but that at another space, nothing excepting pebbles, was poured forth. — I rather incline to a sudden violence. — Unquestionably the distinct phenomenon of the great blocks, which show such unusually

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(a) We meet with the great blocks 67 miles from the mountain & yet retaining an unrounded form. — Now in the Patagonian formation, which clearly was deposited under calm ordinary circumstances, we first meet with good sized rounded pebbles 7 to 8 inches only 55 miles at a distance of only 55 miles. — 5 or 6 miles more to the Eastward they are reduced in size to only a few 1/10th of inch. — This is an argument for some sudden violence. Again it makes in the transporting of the blocks, a subject, which to appears as interesting as difficult to give any sufficient explanation. — The contract of the pebbles dispersion of the pebbles in within & on the surface of the plains is striking & very curious.

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little signs of rolling, have been carried by some sudden tumult: this was probably anterior to the formation of the straits or valley of S. Cruz, & probably to the elevation of the ground: it seems to have happened but once; that is there is no sign of any any anterior violence of a similar nature. — I suppose some would call it Diluvium.

The plain South of the Anchorage (& generally is frequently traversed by many winding valleys: these valleys cannot be perceived excepting by when crossing the plain, you come close to them: they are broard & flat bottomed; their superior extremities are much ramified; an abundance of bushes grow in the lower parts: generally in the very centre, there is a dry small, insignificant water course totally out of any relative size to the valleys. — I believe these little water courses only drain the very water which falls in the very valley; for on the plain it seems to collect in shallow pools & there remain till it is quickly evaporated. — The sea, has been the excavator, I feel very little doubt: At the period of elevation when the level of the edge of the plain was within tidal influence, its outline would be easily modified but I do not see that these valleys could have been formed at the present day

؟ the sea no where winds within the water line of the coast & I see no reason for supposing that it did then: if this might be allowed all difficulty would be removed; but it cannot (?): Mem. Chiloe

the only remaining hypothesis (a) is that the retreating

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(a) waters at the period of elevation caused them: ?

I feel very doubtful how far a body of water rushing from a slope to the ocean could excavate such deep, extensive & regular valleys?? it can only happen once — I do not believe there are submarine valleys? Perhaps the alluvial action is rather greater than I am inclined to believe:

The subject is to me full of difficulty. —

The valleys of course gradually rise to their sources being broard & straight near the coast

If the sea formerly wound in these valleys, as it now does in the Falklands; how totally different the character of the coast was at that time, to what it is now. — N.B. My feeling of unwillingness to believe. that the valleys were excavated by seas: is was owing to thinking it impossible there should be sinuous bays amongst in a soft formation: now I have seen it in Chi[loe] things are changed.

The valleys of Patagonia, especially S. Cruz, belong to the class of Diluvial ones of Buckland. V. Geolog. Trans.1

1 Buckland 1824.


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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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