More Letters of Charles Darwin Volume II

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I have not read Jamieson, or yet got the number. (492/2. Possibly William
Jameson, "Journey from Quito to Cayambe," "Geog. Soc. Journ." Volume XXXI.,
page 184, 1861.) I was very much struck with Forbes' explanation of
n[itrate] of soda beds and the saliferous crust, which I saw and examined
at Iquique. (492/3. "On the Geology of Bolivia and Southern Peru," by D.
Forbes, "Quart. Journ. Geol. Soc." Volume XVII., page 7, 1861. Mr. Forbes
attributes the formation of the saline deposits to lagoons of salt water,
the communication of which with the sea has been cut off by the rising of
the land (loc. cit., page 13).) I often speculated on the greater rise
inland of the Cordilleras, and could never satisfy myself...

I have not read Stur, and am awfully behindhand in many things...(492/4.
The end of this letter is published as a footnote in "Life and Letters,"
II., page 352.)

(FIGURE 5. Map of part of South America and the Galapagos Archipelago.)

LETTER 493. TO C. LYELL.
Down, July 18th [1867].

(493/1. The first part of this letter is published in "Life and Letters,"
III., page 71.)

(493/2. Tahiti (Society Islands) is coloured blue in the map showing the
distribution of the different kinds of reefs in "The Structure and
Distribution of Coral Reefs," Edition III., 1889, page 185. The blue
colour indicates the existence of barrier reefs and atolls which, on
Darwin's theory, point to subsidence.)

Tahiti is, I believe, rightly coloured, for the reefs are so far from the
land, and the ocean so deep, that there must have been subsidence, though
not very recently. I looked carefully, and there is no evidence of recent
elevation. I quite agree with you versus Herschel on Volcanic Islands.
(493/3. Sir John Herschel suggested that the accumulation on the sea-floor
of sediment, derived from the waste of the island, presses down the bed of
the ocean, the continent being on the other hand relieved of pressure;
"this brings about a state of strain in the crust which will crack in its
weakest spot, the heavy side going down, and the light side rising." In
discussing this view Lyell writes ("Principles," Volume II. Edition X.,
page 229), "This hypothesis appears to me of very partial application, for
active volcanoes, even such as are on the borders of continents, are rarely
situated where great deltas have been forming, whether in Pliocene or
post-Tertiary times. The number, also, of active volcanoes in oceanic
islands is very great, not only in the Pacific, but equally in the
Atlantic, where no load of coral matter...can cause a partial weighting and
pressing down of a supposed flexible crust.") Would not the Atlantic and
Antarctic volcanoes be the best examples for you, as there then can be no
coral mud to depress the bottom? In my "Volcanic Islands," page 126, I
just suggest that volcanoes may occur so frequently in the oceanic areas as
the surface would be most likely to crack when first being elevated. I
find one remark, page 128 (493/4. "Volcanic Islands," page 128: "The
islands, moreover, of some of the small volcanic groups, which thus border
continents, are placed in lines related to those along which the adjoining
shores of the continents trend" [see Figure 5].), which seems to me worth
consideration--viz. the parallelism of the lines of eruption in volcanic
archipelagoes with the coast lines of the nearest continent, for this seems
to indicate a mechanical rather than a chemical connection in both cases,
i.e. the lines of disturbance and cracking. In my "South American
Geology," page 185 (493/5. "Geological Observations on South America,"
London, 1846, page 185.), I allude to the remarkable absence at present of
active volcanoes on the east side of the Cordillera in relation to the
absence of the sea on this side. Yet I must own I have long felt a little
sceptical on the proximity of water being the exciting cause. The one
volcano in the interior of Asia is said, I think, to be near great lakes;
but if lakes are so important, why are there not many other volcanoes
within other continents? I have always felt rather inclined to look at the
position of volcanoes on the borders of continents, as resulting from coast
lines being the lines of separation between areas of elevation and
subsidence. But it is useless in me troubling you with my old
speculations.

LETTER 494. TO A.R. WALLACE.
March 22nd [1869].

(494/1. The following extract from a letter to Mr. Wallace refers to his
"Malay Archipelago," 1869.)

I have only one criticism of a general nature, and I am not sure that other
geologists would agree with me. You repeatedly speak as if the pouring out
of lava, etc., from volcanoes actually caused the subsidence of an
adjoining area. I quite agree that areas undergoing opposite movements are
somehow connected; but volcanic outbursts must, I think, be looked at as
mere accidents in the swelling up of a great dome or surface of plutonic
rocks, and there seems no more reason to conclude that such swelling or
elevation in mass is the cause of the subsidence, than that the subsidence
is the cause of the elevation, which latter view is indeed held by some
geologists. I have regretted to find so little about the habits of the
many animals which you have seen.

LETTER 495. TO C. LYELL.
Down, May 20th, 1869.

I have been much pleased to hear that you have been looking at my S.
American book (495/1. "Geological Observations on South America," London,
1846.), which I thought was as completely dead and gone as any pre-Cambrian
fossil. You are right in supposing that my memory about American geology
has grown very hazy. I remember, however, a paper on the Cordillera by D.
Forbes (495/2. "Geology of Bolivia and South Peru," by Forbes, "Quart.
Journ. Geol. Soc." Volume XVII., pages 7-62, 1861. Forbes admits that
there is "the fullest evidence of elevation of the Chile coast since the
arrival of the Spaniards. North of Arica, if we accept the evidence of M.
d'Orbigny and others, the proof of elevation is much more decided; and
consequently it may be possible that here, as is the case about Lima,
according to Darwin, the elevation may have taken place irregularly in
places..." (loc. cit., page 11).), with splendid sections, which I saw in
MS., but whether "referred" to me or lent to me I cannot remember. This
would be well worth your looking to, as I think he both supports and
criticises my views. In Ormerod's Index to the Journal (495/3.
"Classified Index to the Transactions, Proceedings and Quarterly Journal of
the Geological Society."), which I do not possess, you would, no doubt,
find a reference; but I think the sections would be worth borrowing from
Forbes. Domeyko (495/4. Reference is made by Forbes in his paper on
Bolivia and Peru to the work of Ignacio Domeyko on the geology of Chili.
Several papers by this author were published in the "Annales des Mines"
between 1840 and 1869, also in the "Comptes Rendus" of 1861, 1864, etc.)
has published in the "Comptes Rendus papers on Chili, but not, as far as I
can remember, on the structure of the mountains. Forbes, however, would
know. What you say about the plications being steepest in the central and
generally highest part of the range is conclusive to my mind that there has
been the chief axis of disturbance. The lateral thrusting has always
appeared to me fearfully perplexing. I remember formerly thinking that all
lateral flexures probably occurred deep beneath the surface, and have been
brought into view by an enormous superincumbent mass having been denuded.
If a large and deep box were filled with layers of damp paper or clay, and
a blunt wedge was slowly driven up from beneath, would not the layers above
it and on both sides become greatly convoluted, whilst those towards the
top would be only slightly arched? When I spoke of the Andes being
comparatively recent, I suppose that I referred to the absence of the older
formations. In looking to my volume, which I have not done for many years,
I came upon a passage (page 232) which would be worth your looking at, if
you have ever felt perplexed, as I often was, about the sources of volcanic
rocks in mountain chains. You have stirred up old memories, and at the
risk of being a bore I should like to call your attention to another point
which formerly perplexed me much--viz. the presence of basaltic dikes in
most great granitic areas. I cannot but think the explanation given at
page 123 of my "Volcanic Islands" is the true one. (495/5. On page 123 of
the "Geological Observations on the Volcanic Islands visited during the
Voyage of H.M.S. 'Beagle,'" 1844, Darwin quotes several instances of
greenstone and basaltic dikes intersecting granitic and allied metamorphic
rocks. He suggests that these dikes "have been formed by fissures
penetrating into partially cooled rocks of the granitic and metamorphic
series, and by their more fluid parts, consisting chiefly of hornblende
oozing out, and being sucked into such fissures.")

LETTER 496. TO VICTOR CARUS.
Down, March 21st, 1876.

The very kind expressions in your letter have gratified me deeply.

I quite forget what I said about my geological works, but the papers
referred to in your letter are the right ones. I enclose a list with those
which are certainly not worth translating marked with a red line; but
whether those which are not thus marked with a red line are worth
translation you will have to decide. I think much more highly of my book
on "Volcanic Islands" since Mr. Judd, by far the best judge on the subject
in England, has, as I hear, learnt much from it.

I think the short paper on the "formation of mould" is worth translating,
though, if I have time and strength, I hope to write another and longer
paper on the subject.

I can assure you that the idea of any one translating my books better than
you never even momentarily crossed my mind. I am glad that you can give a
fairly good account of your health, or at least that it is not worse.

LETTER 497. TO T. MELLARD READE.
London, December 9th, 1880.

I am sorry to say that I do not return home till the middle of next week,
and as I order no pamphlets to be forwarded to me by post, I cannot return
the "Geolog. Mag." until my return home, nor could my servants pick it out
of the multitude which come by the post. (497/1. Article on "Oceanic
Islands," by T. Mellard Reade, "Geol. Mag." Volume VIII., page 75, 1881.)

As I remarked in a letter to a friend, with whom I was discussing Wallace's
last book (497/2. Wallace's "Island Life," 1880.), the subject to which
you refer seems to me a most perplexing one. The fact which I pointed out
many years ago, that all oceanic islands are volcanic (except St. Paul's,
and now this is viewed by some as the nucleus of an ancient volcano), seems
to me a strong argument that no continent ever occupied the great oceans.
(497/3. "During my investigations on coral reefs I had occasion to consult
the works of many voyagers, and I was invariably struck with the fact that,
with rare exceptions, the innumerable islands scattered through the
Pacific, Indian, and Atlantic Oceans were composed either of volcanic or of
modern coral rocks" ("Geological Observations on Volcanic Islands, etc."
Edition II., 1876, page 140).) Then there comes the statement from the
"Challenger" that all sediment is deposited within one or two hundred miles
from the shores, though I should have thought this rather doubtful with
respect to great rivers like the Amazons.

The chalk formerly seemed to me the best case of an ocean having extended
where a continent now stands; but it seems that some good judges deny that
the chalk is an oceanic deposit. On the whole, I lean to the side that the
continents have since Cambrian times occupied approximately their present
positions. But, as I have said, the question seems a difficult one, and
the more it is discussed the better.

LETTER 498. TO A. AGASSIZ.
Down, January 1st, 1881.

I must write a line or two to thank you much for having written to me so
long a letter on coral reefs at a time when you must have been so busy. Is
it not difficult to avoid believing that the wonderful elevation in the
West Indies must have been accompanied by much subsidence, notwithstanding
the state of Florida? (498/1. The Florida reefs cannot be explained by
subsidence. Alexander Agassiz, who has described these reefs in detail
("Three Cruises of the U.S. Coast and Geodetic Survey Steamer 'Blake,'" 2
volumes, London, 1888), shows that the southern extremity of the peninsula
"is of comparatively recent growth, consisting of concentric barrier-reefs,
which have been gradually converted into land by the accumulation of
intervening mud-flats" (see also Appendix II., page 287, to Darwin's "Coral
Reefs," by T.G. Bonney, Edition III., 1889.)) When reflecting in old days
on the configuration of our continents, the position of mountain chains,
and especially on the long-continued supply of sediment over the same
areas, I used to think (as probably have many other persons) that areas of
elevation and subsidence must as a general rule be separated by a single
great line of fissure, or rather of several closely adjoining lines of
fissure. I mention this because, when looking within more recent times at
charts with the depths of the sea marked by different tints, there seems to
be some connection between the profound depths of the ocean and the trends
of the nearest, though distant, continents; and I have often wished that
some one like yourself, to whom the subject was familiar, would speculate
on it.

P.S.--I do hope that you will re-urge your views about the reappearance of
old characters (498/2. See "Life and Letters," III., pages 245, 246.),
for, as far as I can judge, the most important views are often neglected
unless they are urged and re-urged.

I am greatly indebted to you for sending me very many most valuable works
published at your institution.

2.IX.II. ICE-ACTION, 1841-1882.

LETTER 499. TO C. LYELL.
[1841.]

Your extract has set me puzzling very much, and as I find I am better at
present for not going out, you must let me unload my mind on paper. I
thought everything so beautifully clear about glaciers, but now your case
and Agassiz's statement about the cavities in the rock formed by cascades
in the glaciers, shows me I don't understand their structure at all. I
wish out of pure curiosity I could make it out. (499/1. "Etudes sur les
Glaciers," by Louis Agassiz, 1840, contains a description of cascades (page
343), and "des cavites interieures" (page 348).)

If the glacier travelled on (and it certainly does travel on), and the
water kept cutting back over the edge of the ice, there would be a great
slit in front of the cascade; if the water did not cut back, the whole
hollow and cascade, as you say, must travel on; and do you suppose the next
season it falls down some crevice higher up? In any case, how in the name
of Heaven can it make a hollow in solid rock, which surely must be a work
of many years? I must point out another fact which Agassiz does not, as it
appears to me, leave very clear. He says all the blocks on the surface of
the glaciers are angular, and those in the moraines rounded, yet he says
the medial moraines whence the surface rocks come and are a part [of], are
only two lateral moraines united. Can he refer to terminal moraines alone
when he says fragments in moraines are rounded? What a capital book
Agassiz's is. In [reading] all the early part I gave up entirely the Jura
blocks, and was heartily ashamed of my appendix (499/2. "M. Agassiz has
lately written on the subject of the glaciers and boulders of the Alps. He
clearly proves, as it appears to me, that the presence of the boulders on
the Jura cannot be explained by any debacle, or by the power of ancient
glaciers driving before them moraines...M. Agassiz also denies that they
were transported by floating ice." ("Voyages of the 'Adventure' and
'Beagle,'" Volume III., 1839: "Journal and Remarks: Addenda," page 617.))
(and am so still of the manner in which I presumptuously speak of Agassiz),
but it seems by his own confession that ordinary glaciers could not have
transported the blocks there, and if an hypothesis is to be introduced the
sea is much simpler; floating ice seems to me to account for everything as
well as, and sometimes better than the solid glaciers. The hollows,
however, formed by the ice-cascades appear to me the strongest hostile
fact, though certainly, as you said, one sees hollow round cavities on
present rock-beaches.

I am glad to observe that Agassiz does not pretend that direction of
scratches is hostile to floating ice. By the way, how do you and Buckland
account for the "tails" of diluvium in Scotland? (499/3. Mr. Darwin
speaks of the tails of diluvium in Scotland extending from the protected
side of a hill, of which the opposite side, facing the direction from which
the ice came, is marked by grooves and striae (loc. cit., pages 622, 623).)
I thought in my appendix this made out the strongest argument for rocks
having been scratched by floating ice.

Some facts about boulders in Chiloe will, I think, in a very small degree
elucidate some parts of Jura case. What a grand new feature all this ice
work is in Geology! How old Hutton would have stared! (499/4. Sir
Charles Lyell speaks of the Huttonian theory as being characterised by "the
exclusion of all causes not supposed to belong to the present order of
Nature" (Lyell's "Principles," Edition XII., volume I., page 76, 1875).
Sir Archibald Geikie has recently edited the third volume of Hutton's
"Theory of the Earth," printed by the Geological Society, 1899. See also
"The Founders of Geology," by Sir Archibald Geikie; London, 1897.)

I ought to be ashamed of myself for scribbling on so. Talking of shame, I
have sent a copy of my "Journal" (499/5. "Journal and Remarks," 1832-36.
See note 2, page 148.) with very humble note to Agassiz, as an apology for
the tone I used, though I say, I daresay he has never seen my appendix, or
would care at all about it.

I did not suppose my note about Glen Roy could have been of any use to
you--I merely scribbled what came uppermost. I made one great oversight,
as you would perceive. I forgot the Glacier theory: if a glacier most
gradually disappeared from mouth of Spean Valley [this] would account for
buttresses of shingle below lowest shelf. The difficulty I put about the
ice-barrier of the middle Glen Roy shelf keeping so long at exactly same
level does certainly appear to me insuperable. (499/5. For a description
of the shelves or parallel roads in Glen Roy see Darwin's "Observations on
the Parallel Roads of Glen Roy, etc." "Phil. Trans. R. Soc." 1839, page
39; also Letter 517 et seq.)

What a wonderful fact this breakdown of old Niagara is. How it disturbs
the calculations about lengths of time before the river would have reached
the lakes.

I hope Mrs. Lyell will read this to you, then I shall trust for forgiveness
for having scribbled so much. I should have sent back Agassiz sooner, but
my servant has been very unwell. Emma is going on pretty well.

My paper on South American boulders and "till," which latter deposit is
perfectly characterised in Tierra del Fuego, is progressing rapidly.
(499/6. "On the Distribution of the Erratic Boulders and on the
Contemporaneous Unstratified Deposits of South America," "Trans. Geol.
Soc." Volume VI., page 415, 1842.)

I much like the term post-Pliocene, and will use it in my present paper
several times.

P.S.--I should have thought that the most obvious objection to the marine-
beach theory for Glen Roy would be the limited extension of the shelves.
Though certainly this is not a valid one, after an intermediate one, only
half a mile in length, and nowhere else appearing, even in the valley of
Glen Roy itself, has been shown to exist.

LETTER 500. TO C. LYELL.
1842.

I had some talk with Murchison, who has been on a flying visit into Wales,
and he can see no traces of glaciers, but only of the trickling of water
and of the roots of the heath. It is enough to make an extraneous man
think Geology from beginning to end a work of imagination, and not founded
on observation. Lonsdale, I observe, pays Buckland and myself the
compliment of thinking Murchison not seeing as worth nothing; but I confess
I am astonished, so glaringly clear after two or three days did the
evidence appear to me. Have you seen last "New Edin. Phil. Journ.", it is
ice and glaciers almost from beginning to end. (500/1. "The Edinburgh New
Philosophical Journal," Volume XXXIII. (April-October), 1842, contains
papers by Sir G.S. Mackenzie, Prof. H.G. Brown, Jean de Charpentier,
Roderick Murchison, Louis Agassiz, all dealing with glaciers or ice; also
letters to the Editor relating to Prof. Forbes' account of his recent
observations on Glaciers, and a paper by Charles Darwin entitled "Notes on
the Effects produced by the Ancient Glaciers of Carnarvonshire, and on the
Boulders transported by Floating Ice.") Agassiz says he saw (and has laid
down) the two lowest terraces of Glen Roy in the valley of the Spean,
opposite mouth of Glen Roy itself, where no one else has seen them. (500/2.
"The Glacial Theory and its Recent Progress," by Louis Agassiz, loc. cit.,
page 216. Agassiz describes the parallel terraces on the flanks of Glen
Roy and Glen Spean (page 236), and expresses himself convinced "that the
Glacial theory alone satisfies all the exigencies of the phenomenon" of the
parallel roads.) I carefully examined that spot, owing to the sheep tracks
[being] nearly but not quite parallel to the terrace. So much, again, for
difference of observation. I do not pretend to say who is right.

LETTER 501. TO J.D. HOOKER.
Down, October 12th, 1849.

I was heartily glad to get your last letter; but on my life your thanks for
my very few and very dull letters quite scalded me. I have been very
indolent and selfish in not having oftener written to you and kept my ears
open for news which would have interested you; but I have not forgotten
you. Two days after receiving your letter, there was a short leading
notice about you in the "Gardeners' Chronicle" (501/1. The "Gardeners'
Chronicle," 1849, page 628.); in which it is said you have discovered a
noble crimson rose and thirty rhododendrons. I must heartily congratulate
you on these discoveries, which will interest the public; and I have no
doubt that you will have made plenty of most interesting botanical
observations. This last letter shall be put with all your others, which
are now safe together. I am very glad that you have got minute details
about the terraces in the valleys: your description sounds curiously like
the terraces in the Cordillera of Chili; these latter, however, are single
in each valley; but you will hereafter see a description of these terraces
in my "Geology of S. America." (501/2. "Geological Observations," pages
10 et passim.) At the end of your letter you speak about giving up
Geology, but you must not think of it; I am sure your observations will be
very interesting. Your account of the great dam in the Yangma valley is
most curious, and quite full; I find that I did not at all understand its
wonderful structure in your former letter. Your notion of glaciers pushing
detritus into deep fiords (and ice floating fragments on their channels),
is in many respects new to me; but I cannot help believing your dam is a
lateral moraine: I can hardly persuade myself that the remains of floating
ice action, at a period so immensely remote as when the Himalaya stood at a
low level in the sea, would now be distinguishable. (501/3. Hooker's
"Himalayan Journals," Volume II., page 121, 1854. In describing certain
deposits in the Lachoong valley, Hooker writes: "Glaciers might have
forced immense beds of gravel into positions that would dam up lakes
between the ice and the flanks of the valley" (page 121). In a footnote he
adds: "We are still very ignorant of many details of ice action, and
especially of the origin of many enormous deposits which are not true
moraines." Such deposits are referred to as occurring in the Yangma
valley.) Your not having found scored boulders and solid rocks is an
objection both to glaciers and floating ice; for it is certain that both
produce such. I believe no rocks escape scoring, polishing and
mammillation in the Alps, though some lose it easily when exposed. Are you
familiar with appearance of ice-action? If I understand rightly, you
object to the great dam having been produced by a glacier, owing to the
dryness of the lateral valley and general infrequency of glaciers in
Himalaya; but pray observe that we may fairly (from what we see in Europe)
assume that the climate was formerly colder in India, and when the land
stood at a lower height more snow might have fallen. Oddly enough, I am
now inclined to believe that I saw a gigantic moraine crossing a valley,
and formerly causing a lake above it in one of the great valleys (Valle del
Yeso) of the Cordillera: it is a mountain of detritus, which has puzzled
me. If you have any further opportunities, do look for scores on steep
faces of rock; and here and there remove turf or matted parts to have a
look. Again I beg, do not give up Geology:--I wish you had Agassiz's work
and plates on Glaciers. (501/4. "Etudes sur les Glaciers." L. Agassiz,
Neuchatel, 1840.) I am extremely sorry that the Rajah, ill luck to him,
has prevented your crossing to Thibet; but you seem to have seen most
interesting country: one is astonished to hear of Fuegian climate in
India. I heard from the Sabines that you were thinking of giving up
Borneo; I hope that this report may prove true.