More Letters of Charles Darwin Volume II
by
Charles Darwin
Part 4 out of 14
remembers that he once maintained before the British Association that the
chalk was all deposited at once.
With respect to the insects of Chili, I knew only from Bates that the
species of Carabus showed no special affinity to northern species; from the
great difference of climate and vegetation I should not have expected that
many insects would have shown such affinity. It is more remarkable that
the birds on the broad and lofty Cordillera of Tropical S. America show no
affinity with European species. The little power of diffusion with birds
has often struck me as a most singular fact--even more singular than the
great power of diffusion with plants. Remember that we hope to see you in
the autumn.
P.S.--There is a capital paper in the September number of "Annals and
Magazine," translated from Pictet and Humbert, on Fossil Fish of Lebanon,
but you will, I daresay, have received the original. (507/2. "Recent
Researches on the Fossil Fishes of Mount Lebanon," "Ann. Mag. Nat. Hist."
Volume XVIII., page 237, 1866.) It is capital in relation to modification
of species; I would not wish for more confirmatory facts, though there is
no direct allusion to the modification of species. Hooker, by the way,
gave an admirable lecture at Nottingham; I read it in MS., or rather, heard
it. I am glad it will be published, for it was capital. (507/3. Sir
Joseph Hooker delivered a lecture at the Nottingham meeting of the British
Association (1866) on "Insular Floras," published in the "Gardeners'
Chronicle," 1867. See Letters 366-377, etc.)
Sunday morning.
P.S.--I have just received a letter from Asa Gray with the following
passage, so that, according to this, I am the chief cause of Agassiz's
absurd views:--
"Agassiz is back (I have not seen him), and he went at once down to the
National Academy of Sciences, from which I sedulously keep away, and, I
hear, proved to them that the Glacial period covered the whole continent of
America with unbroken ice, and closed with a significant gesture and the
remark: 'So here is the end of the Darwin theory.' How do you like that?
"I said last winter that Agassiz was bent on covering the whole continent
with ice, and that the motive of the discovery he was sure to make was to
make sure that there should be no coming down of any terrestrial life from
Tertiary or post-Tertiary period to ours. You cannot deny that he has done
his work effectually in a truly imperial way."
LETTER 508. TO C. LYELL.
Down, July 14th, 1868.
Mr. Agassiz's book has been read aloud to me, and I am wonderfully
perplexed what to think about his precise statements of the existence of
glaciers in the Ceara Mountains, and about the drift formation near Rio.
(508/1. "Sur la Geologie de l'Amazone," by MM. Agassiz and Continho,
"Bull. Soc. Geol. France," Volume XXV., page 685, 1868. See also "A
Journey in Brazil," by Professor and Mrs. Louis Agassiz, Boston, 1868.)
There is a sad want of details. Thus he never mentions whether any of the
blocks are angular, nor whether the embedded rounded boulders, which cannot
all be disintegrated, are scored. Yet how can so experienced an observer
as A. be deceived about lateral and terminal moraines? If there really
were glaciers in the Ceara Mountains, it seems to me one of the most
important facts in the history of the inorganic and organic world ever
observed. Whether true or not, it will be widely believed, and until
finally decided will greatly interfere with future progress on many points.
I have made these remarks in the hope that you will coincide. If so, do
you think it would be possible to persuade some known man, such as Ramsay,
or, what would be far better, some two men, to go out for a summer trip,
which would be in many respects delightful, for the sole object of
observing these phenomena in the Ceara Mountains, and if possible also near
Rio? I would gladly put my name down for 50 pounds in aid of the expense
of travelling. Do turn this over in your mind. I am so very sorry not to
have seen you this summer, but for the last three weeks I have been good
for nothing, and have had to stop almost all work. I hope we may meet in
the autumn.
LETTER 509. TO JAMES CROLL.
Down, November 24th, 1868.
I have read with the greatest interest the last paper which you have kindly
sent me. (509/1. Croll discussed the power of icebergs as grinding and
striating agents in the latter part of a paper ("On Geological Time, and
the probable Dates of the Glacial and the Upper Miocene Period") published
in the "Philosophical Magazine," Volume XXXV., page 363, 1868, Volume
XXXVI., pages 141, 362, 1868. His conclusion was that the advocates of the
Iceberg theory had formed "too extravagant notions regarding the potency of
floating ice as a striating agent.") If we are to admit that all the
scored rocks throughout the more level parts of the United States result
from true glacier action, it is a most wonderful conclusion, and you
certainly make out a very strong case; so I suppose I must give up one more
cherished belief. But my object in writing is to trespass on your kindness
and ask a question, which I daresay I could answer for myself by reading
more carefully, as I hope hereafter to do, all your papers; but I shall
feel much more confidence in a brief reply from you. Am I right in
supposing that you believe that the glacial periods have always occurred
alternately in the northern and southern hemispheres, so that the erratic
deposits which I have described in the southern parts of America, and the
glacial work in New Zealand, could not have been simultaneous with our
Glacial period? From the glacial deposits occurring all round the northern
hemisphere, and from such deposits appearing in S. America to be as recent
as in the north, and lastly, from there being some evidence of the former
lower descent of glaciers all along the Cordilleras, I inferred that the
whole world was at this period cooler. It did not appear to me justifiable
without distinct evidence to suppose that the N. and S. glacial deposits
belonged to distinct epochs, though it would have been an immense relief to
my mind if I could have assumed that this had been the case. Secondly, do
you believe that during the Glacial period in one hemisphere the opposite
hemisphere actually becomes warmer, or does it merely retain the same
temperature as before? I do not ask these questions out of mere curiosity;
but I have to prepare a new edition of my "Origin of Species," and am
anxious to say a few words on this subject on your authority. I hope that
you will excuse my troubling you.
LETTER 510. TO J. CROLL.
Down, January 31st, 1869.
To-morrow I will return registered your book, which I have kept so long. I
am most sincerely obliged for its loan, and especially for the MS., without
which I should have been afraid of making mistakes. If you require it, the
MS. shall be returned. Your results have been of more use to me than, I
think, any other set of papers which I can remember. Sir C. Lyell, who is
staying here, is very unwilling to admit the greater warmth of the S.
hemisphere during the Glacial period in the N.; but, as I have told him,
this conclusion which you have arrived at from physical considerations,
explains so well whole classes of facts in distribution, that I must
joyfully accept it; indeed, I go so far as to think that your conclusion is
strengthened by the facts in distribution. Your discussion on the flowing
of the great ice-cap southward is most interesting. I suppose that you
have read Mr. Moseley's recent discussion on the force of gravity being
quite insufficient to account for the downward movement of glaciers (510/1.
Canon Henry Moseley, "On the Mechanical Impossibility of the Descent of
Glaciers by their Weight only." "Proc. R. Soc." Volume XVII., page 202,
1869; "Phil. Mag." Volume XXXVII., page 229, 1869.): if he is right, do
you not think that the unknown force may make more intelligible the
extension of the great northern ice-cap? Notwithstanding your excellent
remarks on the work which can be effected within the million years (510/2.
In his paper "On Geological Time, and the probable Date of the Glacial and
the Upper Miocene Period" ("Phil. Mag." Volume XXXV., page 363, 1868),
Croll endeavours to convey to the mind some idea of what a million years
really is: "Take a narrow strip of paper, an inch broad or more, and 83
feet 4 inches in length, and stretch it along the wall of a large hall, or
round the walls of an apartment somewhat over 20 feet square. Recall to
memory the days of your boyhood, so as to get some adequate conception of
what a period of a hundred years is. Then mark off from one of the ends of
the strip one-tenth of an inch. The one-tenth of an inch will then
represent a hundred years, and the entire length of the strip a million of
years" (loc. cit., page 375).), I am greatly troubled at the short duration
of the world according to Sir W. Thomson (510/3. In a paper communicated
to the Royal Society of Edinburgh, Lord Kelvin (then Sir William Thomson)
stated his belief that the age of our planet must be more than twenty
millions of years, but not more than four hundred millions of years
("Trans. R. Soc. Edinb." Volume XXIII., page 157, 1861, "On the Secular
Cooling of the Earth."). This subject has been recently dealt with by Sir
Archibald Geikie in his address as President of the Geological Section of
the British Association, 1899 ("Brit. Assoc. Report," Dover Meeting, 1899,
page 718).), for I require for my theoretical views a very long period
BEFORE the Cambrian formation. If it would not trouble you, I should like
to hear what you think of Lyell's remark on the magnetic force which comes
from the sun to the earth: might not this penetrate the crust of the earth
and then be converted into heat? This would give a somewhat longer time
during which the crust might have been solid; and this is the argument on
which Sir W. Thomson seems chiefly to rest. You seem to argue chiefly on
the expenditure of energy of all kinds by the sun, and in this respect
Lyell's remark would have no bearing.
My new edition of the "Origin" (510/4. Fifth edition, May, 1869.) will be
published, I suppose, in about two months, and for the chance of your
liking to have a copy I will send one.
P.S.--I wish that you would turn your astronomical knowledge to the
consideration whether the form of the globe does not become periodically
slightly changed, so as to account for the many repeated ups and downs of
the surface in all parts of the world. I have always thought that some
cosmical cause would some day be discovered.
LETTER 511. TO C. LYELL.
Down, July 12th [1872].
I have been glad to see the enclosed and return it. It seems to me very
cool in Agassiz to doubt the recent upheaval of Patagonia, without having
visited any part; and he entirely misrepresents me in saying that I infer
upheaval from the form of the land, as I trusted entirely to shells
embedded and on the surface. It is simply monstrous to suppose that the
terraces stretching on a dead level for leagues along the coast, and miles
in breadth, and covered with beds of stratified gravel, 10 to 30 feet in
thickness, are due to subaerial denudation.
As for the pond of salt-water twice or thrice the density of sea-water, and
nearly dry, containing sea-shells in the same relative proportions as on
the adjoining coast, it almost passes my belief. Could there have been a
lively midshipman on board, who in the morning stocked the pool from the
adjoining coast?
As for glaciation, I will not venture to express any opinion, for when in
S. America I knew nothing about glaciers, and perhaps attributed much to
icebergs which ought to be attributed to glaciers. On the other hand,
Agassiz seems to me mad about glaciers, and apparently never thinks of
drift ice.
I did see one clear case of former great extension of a glacier in T. del
Fuego.
LETTER 512. TO J. GEIKIE.
(512/1. The following letter was in reply to a request from Prof. James
Geikie for permission to publish Mr. Darwin's views, communicated in a
previous letter (November 1876), on the vertical position of stones in
gravelly drift near Southampton. Prof. Geikie wrote (July 15th, 1880):
"You may remember that you attributed the peculiar position of those stones
to differential movements in the drift itself arising from the slow melting
of beds of frozen snow interstratified into the gravels...I have found this
explanation of great service even in Scotland, and from what I have seen of
the drift-gravels in various parts of southern England and northern France,
I am inclined to think that it has a wide application.")
Down, July 19th, 1880.
Your letter has pleased me very much, and I truly feel it an honour that
anything which I wrote on the drift, etc., should have been of the least
use or interest to you. Pray make any use of my letter (512/2. Professor
James Geikie quotes the letter in "Prehistoric Europe," London, 1881 (page
141). Practically the whole of it is given in the "Life and Letters,"
III., page 213.): I forget whether it was written carefully or clearly, so
pray touch up any passages that you may think fit to quote.
All that I have seen since near Southampton and elsewhere has strengthened
my notion. Here I live on a chalk platform gently sloping down from the
edge of the escarptment to the south (512/3. Id est, sloping down from the
escarpment which is to the south.) (which is about 800 feet in height) to
beneath the Tertiary beds to the north. The (512/4. From here to the end
of the paragraph is quoted by Prof. Geikie, loc. cit., page 142.) beds of
the large and broad valleys (and only of these) are covered with an immense
mass of closely packed broken and angular flints; in which mass the skull
of the musk-ox [musk-sheep] and woolly elephant have been found. This
great accumulation of unworn flints must therefore have been made when the
climate was cold, and I believe it can be accounted for by the larger
valleys having been filled up to a great depth during a large part of the
year with drifted frozen snow, over which rubbish from the upper parts of
the platforms was washed by the summer rains, sometimes along one line and
sometimes along another, or in channels cut through the snow all along the
main course of the broad valleys.
I suppose that I formerly mentioned to you the frequent upright position of
elongated flints in the red clayey residue over the chalk, which residue
gradually subsides into the troughs and pipes corroded in the solid chalk.
This letter is very untidy, but I am tired.
P.S. Several palaeolithic celts have recently been found in the great
angular gravel-bed near Southampton in several places.
LETTER 513. TO D. MACKINTOSH.
Down, November 13th, 1880.
Your discovery is a very interesting one, and I congratulate you on it.
(513/1. "On the Precise Mode of Accumulation and Derivation of the Moel-
Tryfan Shelly Deposits; on the Discovery of Similar High-level Deposits
along the Eastern Slopes of the Welsh Mountains; and on the Existence of
Drift-Zones, showing probable Variations in the Rate of Submergence." By
D. Mackintosh, "Quart. Journ. Geol. Soc." Volume XXXVII., pages 351-69,
1881. [Read April 27th, 1881.]) I failed to find shells on Moel Tryfan,
but was interested by finding ("Philosoph. Mag." 3rd series, Volume XXI.,
page 184) shattered rocks (513/2. In reviewing the work by previous
writers on the Moel-Tryfan deposits, Mackintosh refers to Darwin's "very
suggestive description of the Moel-Tryfan deposits...Under the drift he saw
that the surface of the slate, TO A DEPTH OF SEVERAL FEET, HAD BEEN
SHATTERED AND CONTORTED IN A VERY PECULIAR MANNER." The contortion of the
slate, which Mackintosh regarded as "the most interesting of the Moel-
Tryfan phenomena," had not previously been regarded as "sufficiently
striking to arrest attention" by any geologist except Darwin. The
Pleistocene gravel and sand containing marine shells on Moel-Tryfan, about
five miles south-east of Caernarvon, have been the subject of considerable
controversy. By some geologists the drift deposits have been regarded as
evidence of a great submergence in post-Pliocene times, while others have
explained their occurrence at a height of 1300 feet by assuming that the
gravel and sand had been thrust uphill by an advancing ice-sheet. (See
H.B. Woodward, "Geology of England and Wales," Edition II., 1887, pages
491, 492.) Darwin attributed the shattering and contorting of the slates
below the drift to "icebergs grating over the surface.") and far-distant
rounded boulders, which I attributed to the violent impact of icebergs or
coast-ice. I can offer no opinion on whether the more recent changes of
level in England were or were not accompanied by earthquakes. It does not
seem to me a correct expression (which you use probably from haste in your
note) to speak of elevations or depressions as caused by earthquakes: I
suppose that every one admits that an earthquake is merely the vibration
from the fractured crust when it yields to an upward or downward force. I
must confess that of late years I have often begun to suspect (especially
when I think of the step-like plains of Patagonia, the heights of which
were measured by me) that many of the changes of level in the land are due
to changes of level in the sea. (513/3. This view is an agreement with
the theory recently put forward by Suess in his "Antlitz der Erde" (Prag
and Leipzig, 1885). Suess believes that "the local invasions and
transgressions of the continental areas by the sea" are due to "secular
movements of the hydrosphere itself." (See J. Geikie, F.R.S., Presidential
Address before Section E at the Edinburgh Meeting of the British
Association, "Annual Report," page 794.) I suppose that there can be no
doubt that when there was much ice piled up in the Arctic regions the sea
would be attracted to them, and the land on the temperate regions would
thus appear to have risen. There would also be some lowering of the sea by
evaporation and the fixing of the water as ice near the Pole.
I shall read your paper with much interest when published.
LETTER 514. TO J. GEIKIE.
Down, December 13th, 1880.
You must allow me the pleasure of thanking you for the great interest with
which I have read your "Prehistoric Europe." (514/1. "Prehistoric Europe:
a Geological Sketch," London, 1881.) Nothing has struck me more than the
accumulated evidence of interglacial periods, and assuredly the
establishment of such periods is of paramount importance for understanding
all the later changes of the earth's surface. Reading your book has
brought vividly before my mind the state of knowledge, or rather ignorance,
half a century ago, when all superficial matter was classed as diluvium,
and not considered worthy of the attention of a geologist. If you can
spare the time (though I ask out of mere idle curiosity) I should like to
hear what you think of Mr. Mackintosh's paper, illustrated by a little map
with lines showing the courses or sources of the erratic boulders over the
midland counties of England. (514/2. "Results of a Systematic Survey, in
1878, of the Directions and Limits of Dispersion, Mode of Occurrence, and
Relation to Drift-Deposits of the Erratic Blocks or Boulders of the West of
England and East of Wales, including a Revision of Many Years' Previous
Observations," D. Mackintosh, "Quart. Journ. Geol. Soc." Volume XXXV., page
425, 1879.) It is a little suspicious their ending rather abruptly near
Wolverhampton, yet I must think that they were transported by floating ice.
Fifty years ago I knew Shropshire well, and cannot remember anything like
till, but abundance of gravel and sand beds, with recent marine shells. A
great boulder (514/3. Mackintosh alludes (loc. cit., page 442) to felstone
boulders around Ashley Heath, the highest ground between the Pennine and
Welsh Hills north of the Wrekin; also to a boulder on the summit of the
eminence (774 feet above sea-level), "probably the same as that noticed
many years ago by Mr. Darwin." In a later paper, "On the Correlation of
the Drift-Deposits of the North-West of England with those of the Midland
and Eastern Counties" ("Quart. Journ. Geol. Soc." Volume XXXVI., page 178,
1880) Mackintosh mentions a letter received from Darwin, "who was the first
to elucidate the boulder-transporting agency of floating ice," containing
an account of the great Ashley Heath boulder, which he was the first to
discover and expose,...so as to find that the block rested on fragments of
New Red Sandstone, one of which was split into two and deeply scored...The
facts mentioned in the letter from Mr. Darwin would seem to show that the
boulder must have fallen through water from floating ice with a force
sufficient to split the underlying lump of sandstone, but not sufficient to
crush it.") which I had undermined on the summit of Ashley Heath, 720 (?)
feet above the sea, rested on clean blocks of the underlying red sandstone.
I was also greatly interested by your long discussion on the Loss (514/4.
For an account of the Loss of German geologists--"a fine-grained, more or
less homogeneous, consistent, non-plastic loam, consisting of an intimate
admixture of clay and carbonate of lime," see J. Geikie, loc. cit., page
144 et seq.); but I do not feel satisfied that all has been made out about
it. I saw much brick-earth near Southampton in some manner connected with
the angular gravel, but had not strength enough to make out relations. It
might be worth your while to bear in mind the possibility of fine sediment
washed over and interstratified with thick beds of frozen snow, and
therefore ultimately dropped irrespective of the present contour of the
country.
I remember as a boy that it was said that the floods of the Severn were
more muddy when the floods were caused by melting snow than from the
heaviest rains; but why this should be I cannot see.
Another subject has interested me much--viz. the sliding and travelling of
angular debris. Ever since seeing the "streams of stones" at the Falkland
Islands (514/5. "Geological Observations on South America" (1846), page 19
et seq.), I have felt uneasy in my mind on this subject. I wish Mr. Kerr's
notion could be fully elucidated about frozen snow. Some one ought to
observe the movements of the fields of snow which supply the glaciers in
Switzerland.
Yours is a grand book, and I thank you heartily for the instruction and
pleasure which it has given me.
For heaven's sake forgive the untidiness of this whole note.
LETTER 515. TO JOHN LUBBOCK [Lord Avebury].
Down, November 6th, 1881.
If I had written your Address (515/1. Address delivered by Lord Avebury as
President of the British Association at York in 1881. Dr. Hicks is
mentioned as having classed the pre-Cambrian strata in "four great groups
of immense thickness and implying a great lapse of time" and giving no
evidence of life. Hicks' third formation was named by him the Arvonian
("Quart. Journ. Geol. Soc." Volume XXXVII., 1881, Proc., page 55.) (but
this requires a fearful stretch of imagination on my part) I should not
alter what I had said about Hicks. You have the support of the President
[of the] Geological Society (515/2. Robert Etheridge.), and I think that
Hicks is more likely to be right than X. The latter seems to me to belong
to the class of objectors general. If Hicks should be hereafter proved to
be wrong about this third formation, it would signify very little to you.
I forget whether you go as far as to support Ramsay about lakes as large as
the Italian ones: if so, I would myself modify the passage a little, for
these great lakes have always made me tremble for Ramsay, yet some of the
American geologists support him about the still larger N. American lakes.
I have always believed in the main in Ramsay's views from the date of
publication, and argued the point with Lyell, and am convinced that it is a
very interesting step in Geology, and that you were quite right to allude
to it. (515/3. "Glacial Origin of Lakes in Switzerland, Black Forest,
etc." ("Quart. Journ. Geol. Soc." Volume XVIII., pages 185-204, 1862).
Sir John Lubbock (Lord Avebury) gives a brief statement of Ramsay's views
concerning the origin of lakes (Presidential Address, Brit. Assoc. 1881,
page 22): "Prof. Ramsay divides lakes into three classes: (1) Those which
are due to irregular accumulations of drift, and which are generally quite
shallow; (2) those which are formed by moraines; and (3) those which occupy
true basins scooped by glaciers out of the solid rocks. To the latter
class belong, in his opinion, most of the great Swiss and Italian
lakes...Professor Ramsay's theory seems, therefore, to account for a large
number of interesting facts." Sir Archibald Geikie has given a good
summary of Ramsay's theory in his "Memoir of Sir Andrew Crombie Ramsay,"
page 361, London, 1895.)
LETTER 516. TO D. MACKINTOSH.
Down, February 28th, 1882.
I have read professor Geikie's essay, and it certainly appears to me that
he underrated the importance of floating ice. (516/1. "The Intercrossing
of Erratics in Glacial Deposits," by James Geikie, "Scottish Naturalist,"
1881.) Memory extending back for half a century is worth a little, but I
can remember nothing in Shropshire like till or ground moraine, yet I can
distinctly remember the appearance of many sand and gravel beds--in some of
which I found marine shells. I think it would be well worth your while to
insist (but perhaps you have done so) on the absence of till, if absent in
the Western Counties, where you find many erratic boulders.
I was pleased to read the last sentence in Geikie's essay about the value
of your work. (516/2. The concluding paragraph reads as follows: "I
cannot conclude this paper without expressing my admiration for the long-
continued and successful labours of the well-known geologist whose views I
have been controverting. Although I entered my protest against his iceberg
hypothesis, and have freely criticised his theoretical opinions, I most
willingly admit that the results of his unwearied devotion to the study of
those interesting phenomena with which he is so familiar have laid all his
fellow-workers under a debt of gratitude." Mr. Darwin used to speak with
admiration of Mackintosh's work, carried on as it was under considerable
difficulties.)
With respect to the main purport of your note, I hardly know what to say.
Though no evidence worth anything has as yet, in my opinion, been advanced
in favour of a living being, being developed from inorganic matter, yet I
cannot avoid believing the possibility of this will be proved some day in
accordance with the law of continuity. I remember the time, above fifty
years ago, when it was said that no substance found in a living plant or
animal could be produced without the aid of vital forces. As far as
external form is concerned, Eozoon shows how difficult it is to distinguish
between organised and inorganised bodies. If it is ever found that life
can originate on this world, the vital phenomena will come under some
general law of nature. Whether the existence of a conscious God can be
proved from the existence of the so-called laws of nature (i.e., fixed
sequence of events) is a perplexing subject, on which I have often thought,
but cannot see my way clearly. If you have not read W. Graham's "Creed of
Science," (516/3. "The Creed of Science: Religious, Moral, and Social,"
London, 1881.), it would, I think, interest you, and he supports the view
which you are inclined to uphold.
2.IX.III. THE PARALLEL ROADS OF GLEN ROY, 1841-1880.
(517/1. In the bare hilly country of Lochaber, in the Scotch Highlands,
the slopes of the mountains overlooking the vale of Glen Roy are marked by
narrow terraces or parallel roads, which sweep round the shoulders of the
hills with "undeviating horizontality." These roads are described by Sir
Archibald Geikie as having long been "a subject of wonderment and legendary
story among the Highlanders, and for so many years a source of sore
perplexity among men of science." (517/2. "The Scenery of Scotland,"
1887, page 266.) In Glen Roy itself there are three distinct shelves or
terraces, and the mountain sides of the valley of the Spean and other glens
bear traces of these horizontal "roads."
The first important papers dealing with the origin of this striking
physical feature were those of MacCulloch (517/3. "Trans. Geol. Soc."
Volume IV., page 314, 1817.) and Sir Thomas Lauder Dick (517/4. "Trans. R.
Soc. Edinb." Volume IX., page 1, 1823.), in which the writers concluded
that the roads were the shore-lines of lakes which once filled the Lochaber
valleys. Towards the end of June 1838 Mr. Darwin devoted "eight good days"
(517/5. "Life and Letters," I., page 290.) to the examination of the
Lochaber district, and in the following year he communicated a paper to the
Royal Society of London, in which he attributed their origin to the action
of the sea, and regarded them as old sea beaches which had been raised to
their present level by a gradual elevation of the Lochaber district.
In 1840 Louis Agassiz and Buckland (517/6. "Edinb. New Phil. Journal,"
Volume XXXIII., page 236, 1842.) proposed the glacier-ice theory; they
described the valleys as having been filled with lakes dammed back by
glaciers which formed bars across the valleys of Glen Roy, Glen Spean, and
the other glens in which the hill-sides bear traces of old lake-margins.
Agassiz wrote in 1842: "When I visited the parallel roads of Glen Roy with
Dr. Buckland we were convinced that the glacial theory alone satisfied all
the exigencies of the phenomenon." (517/7. Ibid., page 236.)
Mr. David Milne (afterwards Milne-Home) (517/8. "Trans. R. Soc. Edinb."
Volume XVI., page 395, 1847.) in 1847 upheld the view that the ledges
represent the shore-lines of lakes which were imprisoned in the valleys by
dams of detrital material left in the glens during a submergence of 3,000
feet, at the close of the Glacial period. Chambers, in his "Ancient Sea
Margins" (1848), expressed himself in agreement with Mr. Darwin's marine
theory. The Agassiz-Buckland theory was supported by Mr. Jamieson (517/9.
"Quart. Journ. Geol. Soc." Volume XIX., page 235, 1863.), who brought
forward additional evidence in favour of the glacial barriers. Sir Charles
Lyell at first (517/10. "Elements of Geology," Edition II., 1841.)
accepted the explanation given by Mr. Darwin, but afterwards (517/11.
"Antiquity of Man," 1863, pages 252 et seq.) came to the conclusion that
the terrace-lines represent the beaches of glacial lakes. In a paper
published in 1878 (517/12. "Phil. Trans. R. Soc." 1879, page 663.), Prof.
Prestwich stated his acceptance of the lake theory of MacCulloch and Sir T.
Lauder Dick and of the glacial theory of Agassiz, but differed from these
authors in respect of the age of the lakes and the manner of formation of
the roads.
The view that has now gained general acceptance is that the parallel roads
of Glen Roy represent the shores of a lake "that came into being with the
growth of the glaciers and vanished as these melted away." (517/13. Sir
Archibald Geikie, loc. cit., page 269.)
Mr. Darwin became a convert to the glacier theory after the publication of
Mr. Jamieson's paper. He speaks of his own paper as "a great failure"; he
argued in favour of sea action as the cause of the terraces "because no
other explanation was possible under our then state of knowledge."
Convinced of his mistake, Darwin looked upon his error as "a good lesson
never to trust in science to the principle of exclusion." (517/14. "Life
and Letters," I., page 69.)
LETTER 517. TO C. LYELL.
[March 9th, 1841.]
I have just received your note. It is the greatest pleasure to me to write
or talk Geology with you...
I think I have thought over the whole case without prejudice, and remain
firmly convinced they [the parallel roads] are marine beaches. My
principal reason for doing so is what I have urged in my paper (517/15.
"Observations on the Parallel Roads of Glen Roy, and of other parts of
Lochaber in Scotland, with an attempt to prove that they are of Marine
Origin." "Phil. Trans. R. Soc." 1839, page 39.), the buttress-like
accumulations of stratified shingle on sides of valley, especially those
just below the lowest shelf in Spean Valley.
2nd. I can hardly conceive the extension of the glaciers in front of the
valley of Kilfinnin, where I found a new road--where the sides of Great
Glen are not very lofty.
3rd. The flat watersheds which I describe in places where there are no
roads, as well as those connected with "roads." These remain unexplained.
I might continue to add many other such reasons, all of which, however, I
daresay would appear trifling to any one who had not visited the district.
With respect to equable elevation, it cannot be a valid objection to any
one who thinks of Scandinavia or the Pampas. With respect to the glacier
theory, the greatest objection appears to me the following, though possibly
not a sound one. The water has beyond doubt remained very long at the
levels of each shelf--this is unequivocally shown by the depth of the notch
or beach formed in many places in the hard mica-slate, and the large
accumulations or buttresses of well-rounded pebbles at certain spots on the
level of old beaches. (The time must have been immense, if formed by lakes
without tides.) During the existence of the lakes their drainage must have
been at the head of the valleys, and has given the flat appearance of the
watersheds. All this is very clear for four of the shelves (viz., upper
and lower in Glen Roy, the 800-foot one in Glen Spean, and the one in
Kilfinnin), and explains the coincidence of "roads" with the watersheds
more simply than my view, and as simply as the common lake theory. But how
was the Glen Roy lake drained when the water stood at level of the middle
"road"? It must (for there is no other exit whatever) have been drained
over the glacier. Now this shelf is full as narrow in a vertical line and
as deeply worn horizontally into the mountain side and with a large
accumulation of shingle (I can give cases) as the other shelves. We must,
therefore, on the glacier theory, suppose that the surface of the ice
remained at exactly the same level, not being worn down by the running
water, or the glacier moved by its own movement during the very long period
absolutely necessary for a quiet lake to form such a beach as this shelf
presents in its whole course. I do not know whether I have explained
myself clearly. I should like to know what you think of this difficulty.
I shall much like to talk over the Jura case with you. I am tired, so
goodbye.
LETTER 518. TO L. HORNER.
Down [1846].
(518/1. It was agreed at the British Association meeting held at
Southampton in 1846 "That application be made to Her Majesty's Government
to direct that during the progress of the Ordnance Trigonometrical Surveys
in the North of Scotland, the so-called Parallel Roads of Glen Roy and the
adjoining country be accurately surveyed, with the view of determining
whether they are truly parallel and horizontal, the intervening distances,
and their elevations above the present sea-level" ("British Association
Report," 1846, page xix). The survey was undertaken by the Government
Ordnance Survey Office under Col. Sir Henry James, who published the
results in 1874 ("Notes on the Parallel Roads of Glen Roy"); the map on
which the details are given is sheet 63 (one-inch scale).)
In following your suggestion in drawing out something about Glen Roy for
the Geological Committee, I have been completely puzzled how to do it. I
have written down what I should say if I had to meet the head of the Survey
and wished to persuade him to undertake the task; but as I have written it,
it is too long, ill expressed, seems as if it came from nobody and was
going to nobody, and therefore I send it to you in despair, and beg you to
turn the subject in your mind. I feel a conviction if it goes through the
Geological part of Ordnance Survey it will be swamped, and as it is a case
for mere accurate measurements it might, I think without offence, go to the
head of the real Surveyors.
If Agassiz or Buckland are on the Committee they will sneer at the whole
thing and declare the beaches are those of a glacier-lake, than which I am
sure I could convince you that there never was a more futile theory.
I look forward to Southampton (518/2. The British Association meeting
(1846).) with much interest, and hope to hear to-morrow that the lodgings
are secured to us. You cannot think how thoroughly I enjoyed our
geological talks, and the pleasure of seeing Mrs. Horner and yourself here.
(518/3. This letter is published in the privately printed "Memoir of
Leonard Horner," II., page 103.)
[Here follows Darwin's Memorandum.]
The Parallel Roads of Glen Roy, in Scotland, have been the object of
repeated examination, but they have never hitherto been levelled with
sufficient accuracy. Sir T. Lauder Dick (518/4. "On the Parallel Roads of
Lochaber" (with map and plates), by Sir Thomas Lauder Dick, "Trans. R. Soc.
Edinb." Volume IX., page 1, 1823.) procured the assistance of an engineer
for this purpose, but owing to the want of a true ground-plan it was
impossible to ascertain their exact curvature, which, as far as could be
estimated, appeared equal to that of the surface of the sea. Considering
how very rarely the sea has left narrow and well-defined marks of its
action at any considerable height on the land, and more especially
considering the remarkable observations by M. Bravais (518/5. "On the
Lines of Ancient Level of the Sea in Finmark," by M. A. Bravais, translated
from "Voyages de la Commission Scientifique du Nord, etc."; "Quart. Journ.
Geol. Soc." Volume I., page 534, 1845.) on the ancient sea-beaches of
Scandinavia, showing the they are not strictly parallel to each other, and
that the movement has been greater nearer the mountains than on the coast,
it appears highly desirable that the roads of Glen Roy should be examined
with the utmost care during the execution of the Ordnance Survey of
Scotland. The best instruments and the most accurate measurements being
necessary for this end almost precludes the hope of its being ever
undertaken by private individuals; but by the means at the disposal of the
Ordnance, measurements would be easily made even more accurate than those
of M. Bravais. It would be desirable to take two lines of the greatest
possible length in the district, and at nearly right angles to each other,
and to level from the beach at one extremity to that at the other, so that
it might be ascertained whether the curvature does exactly correspond with
that of the globe, or, if not, what is the direction of the line of
greatest elevation. Much attention would be requisite in fixing on either
the upper or lower edge of the ancient beaches as the standard of
measurement, and in rendering this line conspicuous. The heights of the
three roads, one above the other and above the level of the sea, ought to
be accurately ascertained. Mr. Darwin observed one short beach-line north
of Glen Roy, and he has indicated, on the authority of Sir David Brewster,
others in the valley of the Spey. If these could be accurately connected,
by careful measurements of their absolute heights or by levelling, with
those of Glen Roy, it would make a most valuable addition to our knowledge
on this subject. Although the observations here specified would probably
be laborious, yet, considering how rarely such evidence is afforded in any
quarter of the world, it cannot be doubted that one of the most important
problems in Geology--namely, the exact manner in which the crust of the
earth rises in mass--would be much elucidated, and a great service done to
geological science.
LETTER 519. R. CHAMBERS TO D. MILNE-HOME.
St. Andrews, September 7th, 1847.
I have had a letter to-day from Mr. Charles Darwin, beseeching me to obtain
for him a copy of your paper on Glen Roy. (519/1. No doubt Mr. Milne's
paper "On the Parallel Roads of Lochaber," "Trans. R. Soc. Edinb." Volume
XVI., page 395, 1849. [Read March 1st and April 5th, 1847.]) I am sure
you will have pleasure in sending him one; his address is "Down,
Farnborough, Kent." I have again read over your paper carefully, and feel
assured that the careful collection and statement of facts which are found
in it must redound to your credit with all candid persons. The suspicions,
however, which I obtained some time ago as to land-straits and heights of
country being connected with sea-margins and their ordinary memorials still
possesses me, and I am looking forward to some means of further testing the
Glen Roy mystery. If my suspicion turn out true, I shall at once be
regretful on your account, and shall feel it as a great check and
admonition to myself not to be too confident about anything in science till
it has been proved over and over again. The ground hereabouts is now
getting clear of the crops; perhaps when I am in town a few days hence we
may be able to make some appointment for an examination of the beaches of
the district, my list of which has been greatly enlarged during the last
two months.
LETTER 520. TO R. CHAMBERS.
September 11th, 1847.
I hope you will read the first part of my paper before you go [to Glen
Roy], and attend to the manner in which the lines end in Glen Collarig. I
wish Mr. Milne had read it more carefully. He misunderstands me in several
respects, but [I] suppose it is my own fault, for my paper is most
tediously written. Mr. Milne fights me very pleasantly, and I plead guilty
to his rebuke about "demonstration." (520/1. See Letter 521, note.) I do
not know what you think; but Mr. Milne will think me as obstinate as a pig
when I say that I think any barriers of detritus at the mouth of Glen Roy,
Collarig and Glaster more utterly impossible than words can express. I
abide by all that I have written on that head. Conceive such a mass of
detritus having been removed, without great projections being left on each
side, in the very close proximity to every little delta preserved on the
lines of the shelves, even on the shelf 4, which now crosses with uniform
breadth the spot where the barrier stood, with the shelves dying gradually
out, etc. To my mind it is monstrous. Oddly enough, Mr. Milne's
description of the mouth of Loch Treig (I do not believe that valley has
been well examined in its upper end) leaves hardly a doubt that a glacier
descended from it, and, if the roads were formed by a lake of any kind, I
believe it must have been an ice-lake. I have given in detail to Lyell my
several reasons for not thinking ice-lakes probable (520/2. Mr. Darwin
gives some arguments against the glacier theory in the letter (517) to Sir
Charles Lyell; but the letter alluded to is no doubt the one written to
Lyell on "Wednesday, 8th" (Letter 522), in which the reasons are fully
stated.); but to my mind they are incomparably more probable than detritus
of rock-barriers. Have you ever attended to glacier action? After having
seen N. Wales, I can no more doubt the former existence of gigantic
glaciers than I can the sun in the heaven. I could distinguish in N. Wales
to a certain extent icebergs from glacier action (Lyell has shown that
icebergs at the present day score rocks), and I suspect that in Lochaber
the two actions are united, and that the scored rock on the watersheds,
when tideways, were rubbed and bumped by half-stranded icebergs. You will,
no doubt, attend to Glen Glaster. Mr. Milne, I think, does not mention
whether shelf 4 enters it, which I should like to know, and especially he
does not state whether rocks worn on their upper faces are found on the
whole 212 [feet] vertical course of this Glen down to near L. Loggan, or
whether only in the upper part; nor does he state whether these rocks are
scored, or polished, or moutonnees, or whether there are any "perched"
boulders there or elsewhere. I suspect it would be difficult to
distinguish between a river-bed and tidal channel. Mr. Milne's description
of the Pass of Mukkul, expanding to a width of several hundred yards 21
feet deep in the shoalest part, and with a worn islet in the middle, sounds
to me much more like a tidal channel than a river-bed. There must have
been, on the latter view, plenty of fresh water in those days. With
respect to the coincidence of the shelves with the now watersheds, Mr.
Milne only gives half of my explanation. Please read page 65 of my paper.
(520/3. "Observations on the Parallel Roads of Glen Roy, and of other
Parts of Lochaber in Scotland, with an Attempt to Prove that they are of
Marine Origin." "Phil. Trans. R. Soc." 1839, page 39. [Read February 7th,
1839.]) I allude only to the head of Glen Roy and Kilfinnin as silted up.
I did not know Mukkul Pass; and Glen Roy was so much covered up that I did
not search it well, as I was not able to walk very well. It has been an
old conjectural belief of mine that a rising surface becomes stationary,
not suddenly, but by the movement becoming very slow. Now, this would
greatly aid the tidal currents cutting down the passes between the
mountains just before, and to the level of, the stationary periods. The
currents in the fiords in T. del Fuego in a narrow crooked part are often
most violent; in other parts they seem to silt up.
Shall you do any levelling? I believe all the levelling has been [done] in
Glen Roy, nearly parallel to the Great Glen of Scotland. For inequalities
of elevation, the valley of the Spean, at right angles to the apparent axes
of elevation, would be the one to examine. If you go to the head of Glen
Roy, attend to the apparent shelf above the highest one in Glen Roy, lying
on the south side of Loch Spey, and therefore beyond the watershed of Glen
Roy. It would be a crucial case. I was too unwell on that day to examine
it carefully, and I had no levelling instruments. Do these fragments
coincide in level with Glen Gluoy shelf?
MacCulloch talks of one in Glen Turret above the shelf. I could not see
it. These would be important discoveries. But I will write no more, and
pray your forgiveness for this long, ill-written outpouring. I am very
glad you keep to your subject of the terraces. I have lately observed that
you have one great authority (C. Prevost), [not] that authority signifies a
[farthing?] on your side respecting your heretical and damnable doctrine of
the ocean falling. You see I am orthodox to the burning pitch.
LETTER 521. TO D. MILNE-HOME.
Down, [September] 20th, [1847].
I am much obliged by your note. I returned from London on Saturday, and I
found then your memoir (521/1. "On the Parallel Roads of Lochaber, with
Remarks on the Change of Relative Levels of Sea and Land in Scotland, and
on the Detrital Deposits in that Country," "Trans. R. Soc. Edinb." Volume
XVI., page 395, 1849. [Read March 1st and April 5th, 1847.]), which I had
not then received, owing to the porter having been out when I last sent to
the Geological Society. I have read your paper with the greatest interest,
and have been much struck with the novelty and importance of many of your
facts. I beg to thank you for the courteous manner in which you combat me,
and I plead quite guilty to your rebuke about demonstration. (521/2. Mr.
Milne quotes a passage from Mr. Darwin's paper ("Phil. Trans. R. Soc."
1839, page 56), in which the latter speaks of the marine origin of the
parallel roads of Lochaber as appearing to him as having been demonstrated.
Mr. Milne adds: "I regret that Mr. Darwin should have expressed himself in
these very decided and confident terms, especially as his survey was
incomplete; for I venture to think that it can be satisfactorily
established that the parallel roads of Lochaber were formed by fresh-water
lakes" (Milne, loc. cit., page 400).) You have misunderstood my paper on a
few points, but I do not doubt that is owing to its being badly and
tediously written. You will, I fear, think me very obstinate when I say
that I am not in the least convinced about the barriers (521/3. Mr. Milne
believed that the lower parts of the valleys were filled with detritus,
which constituted barriers and thus dammed up the waters into lakes.):
they remain to me as improbable as ever. But the oddest result of your
paper on me (and I assure you, as far as I know myself, it is not
perversity) is that I am very much staggered in favour of the ice-lake
theory of Agassiz and Buckland (521/4. Agassiz and Buckland believed that
the lakes which formed the "roads" were confined by glaciers or moraines.
See "The Glacial Theory and its Recent Progress," by Louis Agassiz, "Edinb.
New Phil. Journ." Volume XXXIII., page 217, 1842 (with map).): until I
read your important discovery of the outlet in Glen Glaster I never thought
this theory at all tenable. (521/5. Mr. Milne discovered that the middle
shelf of Glen Roy, which Mr. Darwin stated was "not on a level with any
watershed" (Darwin, loc. cit., page 43), exactly coincided with a watershed
at the head of Glen Glaster (Milne, loc. cit., page 398).) Now it appears
to me that a very good case can be made in its favour. I am not, however,
as yet a believer in the ice-lake theory, but I tremble for the result. I
have had a good deal of talk with Mr. Lyell on the subject, and from his
advice I am going to send a letter to the "Scotsman," in which I give
briefly my present impression (though there is not space to argue with you
on such points as I think I could argue), and indicate what points strike
me as requiring further investigation with respect, chiefly, to the ice-
lake theory, so that you will not care about it...
P.S.--Some facts mentioned in my "Geology of S. America," page 24 (521/6.
The creeks which penetrate the western shores of Tierra del Fuego are
described as "almost invariably much shallower close to the open sea at
their mouths than inland...This shoalness of the sea-channels near their
entrances probably results from the quantity of sediment formed by the wear
and tear of the outer rocks exposed to the full force of the open sea. I
have no doubt that many lakes--for instance, in Scotland--which are very
deep within, and are separated from the sea apparently only by a tract of
detritus, were originally sea-channels, with banks of this nature near
their mouths, which have since been upheaved" ("Geol. Obs. S. America,"
page 24, footnote.), with regard to the shoaling of the deep fiords of T.
del Fuego near their mouths, and which I have remarked would tend, with a
little elevation, to convert such fiords into lakes with a great mound-like
barrier of detritus at their mouths, might, possibly, have been of use to
you with regard to the lakes of Glen Roy.
LETTER 522. TO C. LYELL.
Down, Wednesday, 8th.
Many thanks for your paper. (522/1. "On the Ancient Glaciers of
Forfarshire." "Proc. Geol. Soc." Volume III., page 337, 1840.) I do
admire your zeal on a subject on which you are not immediately at work. I
will give my opinion as briefly as I can, and I have endeavoured my best to
be honest. Poor Mrs. Lyell will have, I foresee, a long letter to read
aloud, but I will try to write better than usual. Imprimis, it is
provoking that Mr. Milne (522/2. "On the Parallel Roads of Lochaber, etc."
"Trans. R. Soc. Edinb." Volume XVI., page 395, 1849. [Read March 1st and
April 5th, 1847.]) has read my paper (522/3. "Observations on the Parallel
Roads of Glen Roy, etc." "Phil. Trans. R. Soc." 1839, page 39. [Read
February 7th, 1839.].) with little attention, for he makes me say several
things which I do not believe--as, that the water sunk suddenly! (page 10),
that the Valley of Glen Roy, page 13, and Spean was filled up with detritus
to level of the lower shelf, against which there is, I conceive, good
evidence, etc., but I suppose it is the consequence of my paper being most
tediously written. He gives me a just snub for talking of demonstration,
and he fights me in a very pleasant manner. Now for business. I utterly
disbelieve in the barriers (522/4. See note, Letter 521.) for his lakes,
and think he has left that point exactly where it was in the time of
MacCulloch (522/5. "On the Parallel Roads of Glen Roy." "Geol. Trans."
Volume IV., page 314, 1817 (with several maps and sections).) and Dick.
(522/6. "On the Parallel Roads of Lochaber." "Trans. R. Soc. Edinb."
Volume IX., page 1, 1823.) Indeed, in showing that there is a passage at
Glen Glaster at the level of the intermediate shelf, he makes the
difficulty to my mind greater. (522/7. See Letter 521, note.) When I
think of the gradual manner in which the two upper terraces die out at Glen
Collarig and at the mouth of Glen Roy, the smooth rounded form of the hills
there, and the lower shelf retaining its usual width where the immense
barrier stood, I can deliberately repeat "that more convincing proofs of
the non-existence of the imaginary Loch Roy could scarcely have been
invented with full play given to the imagination," etc.: but I do not
adhere to this remark with such strength when applied to the glacier-lake
theory. Oddly, I was never at all staggered by this theory until now,
having read Mr. Milne's argument against it. I now can hardly doubt that a
great glacier did emerge from Loch Treig, and this by the ice itself (not
moraine) might have blocked up the three outlets from Glen Roy. I do not,
however, yet believe in the glacier theory, for reasons which I will
presently give.
There are three chief hostile considerations in Mr. Milne's paper. First,
the Glen [shelf?], not coinciding in height with the upper one [outlet?],
from observations giving 12 feet, 15 feet, 29 feet, 23 feet: if the latter
are correct the terrace must be quite independent, and the case is hostile;
but Mr. Milne shows that there is one in Glen Roy 14 feet below the upper
one, and a second one again (which I observed) beneath this, and then we
come to the proper second shelf. Hence there is no great improbability in
an independent shelf having been found in Glen Gluoy.
This leads me to Mr. Milne's second class of facts (obvious to every one),
namely the non-extension of the three shelves beyond Glen Roy; but I abide
by what I have written on that point, and repeat that if in Glen Roy, where
circumstances have been so favourable for the preservation or formation of
the terraces, a terrace could be formed quite plain for three-quarters of a
mile with hardly a trace elsewhere, we cannot argue, from the non-existence
of shelves, that water did not stand at the same levels in other valleys.
Feeling absolutely convinced that there was no barrier of detritus at the
mouth of Glen Roy, and pretty well convinced that there was none of ice,
the manner in which the terraces die out when entering Glen Spean, which
must have been a tideway, shows on what small circumstances the formation
of these shelves depended. With respect to the non-existence of shelves in
other parts of Scotland, Mr. Milne shows that many others do exist, and
their heights above the sea have not yet been carefully measured, nor have
even those of Glen Roy, which I suspect are all 100 feet too high.
Moreover, according to Bravais (522/8. "On the Lines of Ancient Level of
the Sea in Finmark." By A. Bravais, Member of the Scientific Commission of
the North. "Quart. Journ. Geol. Soc." Volume I., page 534, 1845 (a
translation).), we must not feel sure that either the absolute height or
the intermediate heights between the terraces would be at all the same at
distant points. In levelling the terraces in Lochaber, all, I believe,
have been taken in Glen Roy, nearly N. and S. There should be levels taken
at right angles to this line and to the Great Glen of Scotland or chief
line of elevation.
Thirdly, the nature of the outlets from the supposed lakes. This appears
to me the best and newest part of the paper. If Sir James Clark would like
to attend to any particular points, direct his attention to this:
especially to follow Glen Glaster from Glen Roy to L. Laggan. Mr. Milne
describes this as an old and great river-course with a fall of 212 feet.
He states that the rocks are smooth on upper face and rough on lower, but
he does not mention whether this character prevails throughout the whole
212 vertical feet--a most important consideration; nor does he state
whether these rocks are polished or scratched, as might have happened even
to a considerable depth beneath the water (Mem. great icebergs in narrow
fiords of T. del Fuego (522/9. In the "Voyage of the 'Beagle'" a
description is given of the falling of great masses of ice from the icy
cliffs of the glaciers with a crash that "reverberates like the broadside
of a man-of-war, through the lonely channels" which intersect the
coast-line of Tierra del Fuego. Loc. cit., page 246.)) by the action of
icebergs, for that icebergs transported boulders on to terraces, I have no
doubt. Mr. Milne's description of the outlets of his lake sound to me more
like tidal channels, nor does he give any arguments how such are to be
distinguished from old river-courses. I cannot believe in the body of
fresh water which must, on the lake theory, have flowed out of them. At
the Pass of Mukkul he states that the outlet is 70 feet wide and the rocky
bottom 21 feet below the level of the shelf, and that the gorge expands to
the eastwards into a broad channel of several hundred yards in width,
divided in the middle by what has formerly been a rocky islet, against
which the waters of this large river had chafed in issuing from the pass.
We know the size of the river at the present day which would flow out
through this pass, and it seems to me (and in the other given cases) to be
as inadequate; the whole seems to me far easier explained by a tideway than
by a formerly more humid climate.
With respect to the very remarkable coincidence between the shelves and the
outlets (rendered more remarkable by Mr. Milne's discovery of the outlet to
the intermediate shelf at Glen Glaster (522/10. See Letter 521, note.)),
Mr. Milne gives only half of my explanation; he alludes to (and disputes)
the smoothing and silting-up action, which I still believe in. I state:
If we consider what must take place during the gradual rise of a group of
islands, we shall have the currents endeavouring to cut down and deepen
some shallow parts in the channels as they are successively brought near
the surface, but tending from the opposition of tides to choke up others
with littoral deposits. During a long interval of rest, from the length of
time allowed to the above processes, the tendency would often prove
effective, both in forming, by accumulation of matter, isthmuses, and in
keeping open channels. Hence such isthmuses and channels just kept open
would oftener be formed at the level which the waters held at the interval
of rest, than at any other (page 65). I look at the Pass of Mukkul (21
feet deep, Milne) as a channel just kept open, and the head of Glen Roy
(where there is a great bay silted up) and of Kilfinnin (at both which
places there are level-topped mounds of detritus above the level of the
terraces) as instances of channels filled up at the stationary levels. I
have long thought it a probable conjecture that when a rising surface
becomes stationary it becomes so, not at once, but by the movements first
becoming very slow; this would greatly favour the cutting down many gaps in
the mountains to the level of the stationary periods.
GLACIER THEORY.
If a glacialist admitted that the sea, before the formation of the
terraces, covered the country (which would account for land-straits above
level of terraces), and that the land gradually emerged, and if he supposed
his lakes were banked by ice alone, he would make out, in my opinion, the
best case against the marine origin of the terraces. From the scattered
boulders and till, you and I must look at it as certain that the sea did
cover the whole country, and I abide quite by my arguments from the
buttresses, etc., that water of some kind receded slowly from the valleys
of Lochaber (I presume Mr. Milne admits this). Now, I do not believe in
the ice-lake theory, from the following weak but accumulating reasons:
because, 1st, the receding water must have been that of a lake in Glen
Spean, and of the sea in the other valleys of Scotland, where I saw similar
buttresses at many levels; 2nd, because the outlets of the supposed lakes
as already stated seem, from Mr. Milne's statements, too much worn and too
large; 3rd, when the lake stood at the three-quarters of a mile shelf the
water from it must have flowed over ice itself for a very long time, and
kept at the same exact level: certainly this shelf required a long time
for its formation; 4th, I cannot believe a glacier would have blocked up
the short, very wide valley of Kilfinnin, the Great Glen of Scotland also
being very low there; 5th, the country at some places where Mr. Milne has
described terraces is not mountainous, and the number of ice-lakes appears
to me very improbable; 6th, I do not believe any lake could scoop the rocks
so much as they are at the entrance to Loch Treig or cut them off at the
head of Upper Glen Roy; 7th, the very gradual dying away of the terraces at
the mouth of Glen Roy does not look like a barrier of any kind; 8th, I
should have expected great terminal moraines across the mouth of Glen Roy,
Glen Collarig, and Glaster, at least at the bottom of the valleys. Such, I
feel pretty sure, do not exist.
I fear I must have wearied you with the length of this letter, which I have
not had time to arrange properly. I could argue at great length against
Mr. Milne's theory of barriers of detritus, though I could help him in one
way--viz., by the soundings which occur at the entrances of the deepest
fiords in T. del Fuego. I do not think he gives the smallest satisfaction
with respect to the successive and comparatively sudden breakage of his
many lakes.
Well, I enjoyed my trip to Glen Roy very much, but it was time thrown away.
I heartily wish you would go there; it should be some one who knows glacier
and iceberg action, and sea action well. I wish the Queen would command
you. I had intended being in London to-morrow, but one of my principal
plagues will, I believe, stop me; if I do I will assuredly call on you. I
have not yet read Mr. Milne on Elevation (522/11. "On a Remarkable
Oscillation of the Sea, observed at Various Places on the Coasts of Great
Britain in the First Week of July, 1843." "Trans. R. Soc. Edinb." Volume
XV., page 609, 1844.), so will keep his paper for a day or two.
P.S.--As you cannot want this letter, I wish you would return it to me, as
it will serve as a memorandum for me. Possibly I shall write to Mr.
Chambers, though I do not know whether he will care about what I think on
the subject. This letter is too long and ill-written for Sir J. Clark.
LETTER 523. TO LADY LYELL.
[October 4th, 1847.]
I enclose a letter from Chambers, which has pleased me very much (which
please return), but I cannot feel quite so sure as he does. If the
Lochaber and Tweed roads really turn out exactly on a level, the sea theory
is proved. What a magnificent proof of equality of elevation, which does
not surprise me much; but I fear I see cause of doubt, for as far as I
remember there are numerous terraces, near Galashiels, with small intervals
of height, so that the coincidence of height might be cooked. Chambers
does not seem aware of one very striking coincidence, viz., that I made by
careful measurement my Kilfinnin terrace 1202 feet above sea, and now Glen
Gluoy is 1203 feet, according to the recent more careful measurements.
Even Agassiz (523/1. "On the Glacial Theory," by Louis Agassiz, "Edinb.
New Phil. Journ." Volume XXXIII., page 217, 1842. The parallel terraces
are dealt with by Agassiz, pages 236 et seq.) would be puzzled to block up
Glen Gluoy and Kilfinnin by the same glacier, and then, moreover, the lake
would have two outlets. With respect to the middle terrace of Glen Roy--
seen by Chambers in the Spean (figured by Agassiz, and seen by myself but
not noticed, as I thought it might have been a sheep track)--it might yet
have been formed on the ice-lake theory by two independent glaciers going
across the Spean, but it is very improbable that two such immense ones
should not have been united into one. Chambers, unfortunately, does not
seem to have visited the head of the Spey, and I have written to propose
joining funds and sending some young surveyor there. If my letter is
published in the "Scotsman," how Buckland (523/2. Professor Buckland may
be described as joint author, with Agassiz, of the Glacier theory.), as I
have foreseen, will crow over me: he will tell me he always knew that I
was wrong, but now I shall have rather ridiculously to say, "but I am all
right again."
I have been a good deal interested in Miller (523/3. Hugh Miller's "First
Impressions of England and its People," London, 1847.), but I find it not
quick reading, and Emma has hardly begun it yet. I rather wish the scenic
descriptions were shorter, and that there was a little less geologic
eloquence.
Lyell's picture now hangs over my chimneypiece, and uncommonly glad I am to
have it, and thank you for it.
LETTER 524. TO C. LYELL.
Down, September 6th [1861].
I think the enclosed is worth your reading. I am smashed to atoms about
Glen Roy. My paper was one long gigantic blunder from beginning to end.
Eheu! Eheu! (524/1. See "Life and Letters," I., pages 68, 69, also pages
290, 291.)
LETTER 525. TO C. LYELL.
Down, September 22nd [1861].
I have read Mr. Jamieson's last letter, like the former ones, with very
great interest. (525/1. Mr. Jamieson visited Glen Roy in August 1861 and
in July 1862. His paper "On the Parallel Roads of Glen Roy, and their
Place in the History of the Glacial Period," was published in the
"Quarterly Journal of the Geological Society" in 1863, Volume XIX., page
235. His latest contribution to this subject was published in the
"Quarterly Journal," Volume XLVIII., page 5, 1892.) What a problem you
have in hand! It beats manufacturing new species all to bits. It would be
a great personal consolation to me if Mr. J. can admit the sloping Spean
terrace to be marine, and would remove one of my greatest difficulties--
viz. the vast contrast of Welsh and Lochaber valleys. But then, as far as
I dare trust my observations, the sloping terraces ran far up the Roy
valley, so as to reach not far below the lower shelf. If the sloping
fringes are marine and the shelves lacustrine, all I can say is that nature
has laid a shameful trap to catch an unwary wretch. I suppose that I have
underrated the power of lakes in producing pebbles; this, I think, ought to
be well looked to. I was much struck in Wales on carefully comparing the
glacial scratches under a lake (formed by a moraine and which must have
existed since the Glacial epoch) and above water, and I could perceive NO
difference. I believe I saw many such beds of good pebbles on level of
lower shelf, which at the time I could not believe could have been found on
shores of lake. The land-straits and little cliffs above them, to which I
referred, were quite above the highest shelf; they may be of much more
ancient date than the shelves. Some terrace-like fringes at head of the
Spey strike me as very suspicious. Mr. J. refers to absence of pebbles at
considerable heights: he must remember that every storm, every deer, every
hare which runs tends to roll pebbles down hill, and not one ever goes up
again. I may mention that I particularly alluded to this on S. Ventanao
(525/2. "Geolog. Obs. on South America," page 79. "On the flanks of the
mountains, at a height of 300 or 400 feet above the plain, there were a few
small patches of conglomerate and breccia, firmly cemented by ferruginous
matter to the abrupt and battered face of the quartz--traces being thus
exhibited of ancient sea-action.") in N. Patagonia, a great isolated rugged
quartz-mountain 3,000 feet high, and I could find not one pebble except on
one very small spot, where a ferruginous spring had firmly cemented a few
to the face of mountain. If the Lochaber lakes had been formed by an ice-
period posterior to the (marine?) sloping terraces in the Spean, would not
Mr. J. have noticed gigantic moraines across the valley opposite the
opening of Lake Treig? I go so far as not to like making the elevation of
the land in Wales and Scotland considerably different with respect to the
ice-period, and still more do I dislike it with respect to E. and W.
Scotland. But I may be prejudiced by having been so long accustomed to the
plains of Patagonia. But the equality of level (barring denudation) of
even the Secondary formations in Britain, after so many ups and downs,
always impresses my mind, that, except when the crust-cracks and mountains
are formed, movements of elevation and subsidence are generally very
equable.
But it is folly my scribbling thus. You have a grand problem, and heaven
help you and Mr. Jamieson through it. It is out of my line nowadays, and
above and beyond me.
LETTER 526. TO J.D. HOOKER.
Down, September 28th [1861].
It is, I believe, true that Glen Roy shelves (I remember your Indian
letter) were formed by glacial lakes. I persuaded Mr. Jamieson, an
excellent observer, to go and observe them; and this is his result. There
are some great difficulties to be explained, but I presume this will
ultimately be proved the truth...
LETTER 527. TO C. LYELL.
Down, October 1st [1861].
Thank you for the most interesting correspondence. What a wonderful case
that of Bedford. (527/1. No doubt this refers to the discovery of flint
implements in the Valley of the Ouse, near Bedford, in 1861 (see Lyell's
"Antiquity of Man," pages 163 et seq., 1863.) I thought the problem
sufficiently perplexing before, but now it beats anything I ever heard of.
Far from being able to give any hypothesis for any part, I cannot get the
facts into my mind. What a capital observer and reasoner Mr. Jamieson is.
The only way that I can reconcile my memory of Lochaber with the state of
the Welsh valleys is by imagining a great barrier, formed by a terminal
moraine, at the mouth of the Spean, which the river had to cut slowly
through, as it drained the lowest lake after the Glacial period. This
would, I can suppose, account for the sloping terraces along the Spean. I
further presume that sharp transverse moraines would not be formed under
the waters of the lake, where the glacier came out of L. Treig and abutted
against the opposite side of the valley. A nice mess I made of Glen Roy!
I have no spare copy of my Welsh paper (527/2. "Notes on the Effects
produced by the Ancient Glaciers of Caernarvonshire, and on the Boulders
transported by Floating Ice," "Edinb. New Phil. Journ." Volume XXXIII.,
page 352, 1842.); it would do you no good to lend it. I suppose I thought
that there must have been floating ice on Moel Tryfan. I think it cannot
be disputed that the last event in N. Wales was land-glaciers. I could not
decide where the action of land-glaciers ceased and marine glacial action
commenced at the mouths of the valleys.
What a wonderful case the Bedford case. Does not the N. American view of
warmer or more equable period, after great Glacial period, become much more
probable in Europe?
But I am very poorly to-day, and very stupid, and hate everybody and
everything. One lives only to make blunders. I am going to write a little
book for Murray on Orchids (527/3. "On the Various Contrivances by which
Orchids are Fertilised by Insects," London, 1862.), and to-day I hate them
worse than everything. So farewell, in a sweet frame of mind.
LETTER 528. TO C. LYELL.
Down, October 14th [1861].
I return Jamieson's capital letter. I have no comments, except to say that
he has removed all my difficulties, and that now and for evermore I give up
and abominate Glen Roy and all its belongings. It certainly is a splendid
case, and wonderful monument of the old Ice-period. You ought to give a
woodcut. How many have blundered over those horrid shelves!
That was a capital paper by Jamieson in the last "Geol. Journal." (528/1.
"On the Drift and Rolled Gravel of the North of Scotland," "Quart. Journ.
Geol. Soc." Volume XVI., page 347, 1860.) I was never before fully
convinced of the land glacialisation of Scotland before, though Chambers
tried hard to convince me.
I must say I differ rather about Ramsay's paper; perhaps he pushes it too
far. (528/2. "On the Glacial Origin of Certain Lakes, etc." "Quart.
Journ. Geol. Soc." Volume XVIII., page 185. See Letter 503.) It struck me
the more from remembering some years ago marvelling what could be the
meaning of such a multitude of lakes in Friesland and other northern
districts. Ramsay wrote to me, and I suggested that he ought to compare
mountainous tropical regions with northern regions. I could not remember
many lakes in any mountainous tropical country. When Tyndall talks of
every valley in Switzerland being formed by glaciers, he seems to forget
there are valleys in the tropics; and it is monstrous, in my opinion, the
accounting for the Glacial period in the Alps by greater height of
mountains, and their lessened height, if I understand, by glacial erosion.
"Ne sutor ultra crepidam," I think, applies in this case to him. I am hard
at work on "Variation under Domestication." (528/3. Published 1868.)
P.S.--I am rather overwhelmed with letters at present, and it has just
occurred to me that perhaps you will forward my note to Mr. Jamieson; as it
will show that I entirely yield. I do believe every word in my Glen Roy
paper is false.
LETTER 529. TO C. LYELL.
Down, October 20th [1861].
Notwithstanding the orchids, I have been very glad to see Jamieson's
letter; no doubt, as he says, certainty will soon be reached.
With respect to the minor points of Glen Roy, I cannot feel easy with a
mere barrier of ice; there is so much sloping, stratified detritus in the
valleys. I remember that you somewhere have stated that a running stream
soon cuts deeply into a glacier. I have been hunting up all old references
and pamphlets, etc., on shelves in Scotland, and will send them off to Mr.
J., as they possibly may be of use to him if he continues the subject. The
Eildon Hills ought to be specially examined. Amongst MS. I came across a
very old letter from me to you, in which I say: "If a glacialist admitted
that the sea, before the formation of the shelves, covered the country
(which would account for the land-straits above the level of the shelves),
and if he admitted that the land gradually emerged, and if he supposed that
his lakes were banked up by ice alone, he would make out, in my opinion,
the best case against the marine origin of the shelves." (529/1. See
Letter 522.) This seems very much what you and Mr. J. have come to.
The whole glacial theory is really a magnificent subject.
LETTER 530. TO C. LYELL.
Down, April 1st [1862].
I am not quite sure that I understand your difficulty, so I must give what
seems to me the explanation of the glacial lake theory at some little
length. You know that there is a rocky outlet at the level of all the
shelves. Please look at my map. (530/1. The map accompanying Mr.
Darwin's paper in the "Phil. Trans. R. Soc." 1839.) I suppose whole valley
of Glen Spean filled with ice; then water would escape from an outlet at
Loch Spey, and the highest shelf would be first formed. Secondly, ice
began to retreat, and water will flow for short time over its surface; but
as soon as it retreated from behind the hill marked Craig Dhu, where the
outlet on level of second shelf was discovered by Milne (530/2. See note,
Letter 521.), the water would flow from it and the second shelf would be
formed. This supposes that a vast barrier of ice still remains under Ben
Nevis, along all the lower part of the Spean. Lastly, I suppose the ice
disappeared everywhere along L. Loggan, L. Treig, and Glen Spean, except
close under Ben Nevis, where it still formed a barrier, the water flowing
out at level of lowest shelf by the Pass of Mukkul at head of L. Loggan.
This seems to me to account for everything. It presupposes that the
shelves were formed towards the close of the Glacial period. I come up to
London to read on Thursday a short paper at the Linnean Society. Shall I
call on Friday morning at 9.30 and sit half an hour with you? Pray have no
scruple to send a line to Queen Anne Street to say "No" if it will take
anything out of you. If I do not hear, I will come.
LETTER 531. TO J. PRESTWICH.
Down, January 3rd, 1880.
You are perfectly right. (531/1. Prof. Prestwich's paper on Glen Roy was
published in the "Phil. Trans. R. Soc." for 1879, page 663.) As soon as I
read Mr. Jamieson's article on the parallel roads, I gave up the ghost with
more sighs and groans than on almost any other occasion in my life.
2.IX.IV. CORAL REEFS, FOSSIL AND RECENT, 1841-1881.
LETTER 532. TO C. LYELL.
Shrewsbury, Tuesday, 6th [July, 1841].
Your letter was forwarded me here. I was the more glad to receive it, as I
never dreamed of your being able to find time to write, now that you must
be so very busy; and I had nothing to tell you about myself, else I should
have written. I am pleased to hear how extensive and successful a trip you
appear to have made. You must have worked hard, and got your Silurian
subject well in your head, to have profited by so short an excursion. How
I should have enjoyed to have followed you about the coral-limestone. I
once was close to Wenlock (532/1. The Wenlock limestone (Silurian)
contains an abundance of corals. "The rock seems indeed to have been
formed in part by massive sheets and bunches of coral" (Geikie, "Text-book
of Geology," 1882, page 678.), something such as you describe, and made a
rough drawing, I remember, of the masses of coral. But the degree in which
the whole mass was regularly stratified, and the quantity of mud, made me
think that the reefs could never have been like those in the Pacific, but
that they most resembled those on the east coast of Africa, which seem
(from charts and descriptions) to confine extensive flats and mangrove
swamps with mud, or like some imperfect ones about the West India Islands,
within the reefs of which there are large swamps. All the reefs I have
myself seen could be associated only with nearly pure calcareous rocks. I
have received a description of a reef lying some way off the coast near
Belize (terra firma), where a thick bed of mud seems to have invaded and
covered a coral reef, leaving but very few islets yet free from it. But I
can give you no precise information without my notes (even if then) on
these heads...
Bermuda differs much from any other island I am acquainted with. At first
sight of a chart it resembles an atoll; but it differs from this structure
essentially in the gently shelving bottom of the sea all round to some
distance; in the absence of the defined circular reefs, and, as a
consequence, of the defined central pool or lagoon; and lastly, in the
height of the land. Bermuda seems to be an irregular, circular, flat bank,
encrusted with knolls and reefs of coral, with land formed on one side.
This land seems once to have been more extensive, as on some parts of the
bank farthest removed from the island there are little pinnacles of rock of
the same nature as that of the high larger islands. I cannot pretend to
form any precise notion how the foundation of so anomalous an island has
been produced, but its whole history must be very different from that of
the atolls of the Indian and Pacific oceans--though, as I have said, at
first glance of the charts there is a considerable resemblance.
LETTER 533. TO C. LYELL.
[1842.]
Considering the probability of subsidence in the middle of the great oceans
being very slow; considering in how many spaces, both large ones and small
ones (within areas favourable to the growth of corals), reefs are absent,
which shows that their presence is determined by peculiar conditions;
considering the possible chance of subsidence being more rapid than the
upward growth of the reefs; considering that reefs not very rarely perish
(as I cannot doubt) on part, or round the whole, of some encircled islands
and atolls: considering these things, I admit as very improbable that the
polypifers should continue living on and above the same reef during a
subsidence of very many thousand feet; and therefore that they should form
masses of enormous thickness, say at most above 5,000 feet. (533/1.
"...As we know that some inorganic causes are highly injurious to the
growth of coral, it cannot be expected that during the round of change to
which earth, air, and water are exposed, the reef-building polypifers
should keep alive for perpetuity in any one place; and still less can this
be expected during the progressive subsidences...to which by our theory
these reefs and islands have been subjected, and are liable" ("The
Structure and Distribution of Coral Reefs," page 107: London, 1842).)
This admission, I believe, is in no way fatal to the theory, though it is
so to certain few passages in my book.
In the areas where the large groups of atolls stand, and where likewise a
few scattered atolls stand between such groups, I always imagined that
there must have been great tracts of land, and that on such large tracts
there must have been mountains of immense altitudes. But not, it appears
to me, that one is only justified in supposing that groups of islands stood
there. There are (as I believe) many considerable islands and groups of
islands (Galapagos Islands, Great Britain, Falkland Islands, Marianas, and,
I believe, Viti groups), and likewise the majority of single scattered
islands, all of which a subsidence between 4,000 and 5,000 feet would
entirely submerge or would leave only one or two summits above water, and
hence they would produce either groups of nothing but atolls, or of atolls
with one or two encircled islands. I am far from wishing to say that the
islands of the great oceans have not subsided, or may not continue to
subside, any number of feet, but if the average duration (from all causes
of destruction) of reefs on the same spot is limited, then after this limit
has elapsed the reefs would perish, and if the subsidence continued they
would be carried down; and if the group consisted only of atolls, only open
ocean would be left; if it consisted partly or wholly of encircled islands,
these would be left naked and reefless, but should the area again become
favourable for growth of reefs, new barrier-reefs might be formed round
them. As an illustration of this notion of a certain average duration of
reefs on the same spot, compared with the average rate of subsidence, we
may take the case of Tahiti, an island of 7,000 feet high. Now here the
present barrier-reefs would never be continued upwards into an atoll,
although, should the subsidence continue at a period long after the death
of the present reefs, new ones might be formed high up round its sides and
ultimately over it. The case resolves itself into: what is the ordinary
height of groups of islands, of the size of existing groups of atolls
(excepting as many of the highest islands as there now ordinarily occur
encircling barrier-reefs in the existing groups of atolls)? and likewise
what is the height of the single scattered islands standing between such
groups of islands? Subsidence sufficient to bury all these islands (with
the exception of as many of the highest as there are encircled islands in
the present groups of atolls) my theory absolutely requires, but no more.
To say what amount of subsidence would be required for this end, one ought
to know the height of all existing islands, both single ones and those in
groups, on the face of the globe--and, indeed, of half a dozen worlds like
ours. The reefs may be of much greater [thickness] than that just
sufficient on an average to bury groups of islands; and the probability of
the thickness being greater seems to resolve itself into the average rate
of subsidence allowing upward growth, and average duration of reefs on the
same spot. Who will say what this rate and what this duration is? but till
both are known, we cannot, I think, tell whether we ought to look for
upraised coral formations (putting on one side denudation) above the
unknown limit, say between 3,000 and 5,000 feet, necessary to submerge
groups of common islands. How wretchedly involved do these speculations
become.
LETTER 534. TO E. VON MOJSISOVICS.
Down, January 29th, 1879.
I thank you cordially for the continuation of your fine work on the
Tyrolese Dolomites (534/1. "Dolomitriffe Sudtirols und Venetiens": Wien,
1878.), with its striking engravings and the maps, which are quite
wonderful from the amount of labour which they exhibit, and its extreme
difficulty. I well remember more than forty years ago examining a section
of Silurian limestone containing many corals, and thinking to myself that
it would be for ever impossible to discover whether the ancient corals had
formed atolls or barrier reefs; so you may well believe that your work will
interest me greatly as soon as I can find time to read it. I am much
obliged for your photograph, and from its appearance rejoice to see that
much more good work may be expected from you.
I enclose my own photograph, in case you should like to possess a copy.
LETTER 535. TO A. AGASSIZ.
(535/1. Part of this letter is published in "Life and Letters," III.,
pages 183, 184.)
Down, May 5th, 1881.
It was very good of you to write to me from Tortugas, as I always feel much
interested in hearing what you are about, and in reading your many
discoveries. It is a surprising fact that the peninsula of Florida should
have remained at the same level for the immense period requisite for the
accumulation of so vast a pile of debris. (535/2. Alexander Agassiz
published a paper on "The Tortugas and Florida Reefs" in the "Mem. Amer.
Acad. Arts and Sci." XI., page 107, 1885. See also his "Three Cruises of
the 'Blake,'" Volume I., 1888.)
You will have seen Mr. Murray's views on the formation of atolls and
barrier reefs. (535/3. "On the Structure and Origin of Coral Reefs and
Islands," "Proc. R. Soc. Edin." Volume X., page 505, 1880. Prof. Bonney
has given a summary of Sir John Murray's views in Appendix II. of the third
edition of Darwin's "Coral Reefs," 1889.) Before publishing my book, I
thought long over the same view, but only as far as ordinary marine
organisms are concerned, for at that time little was known of the multitude
of minute oceanic organisms. I rejected this view, as from the few
dredgings made in the 'Beagle' in the S. Temperate regions, I concluded
that shells, the smaller corals, etc., etc., decayed and were dissolved
when not protected by the deposition of sediment; and sediment could not
accumulate in the open ocean. Certainly shells, etc., were in several
cases completely rotten, and crumbled into mud between my fingers; but you
will know well whether this is in any degree common. I have expressly said
that a bank at the proper depth would give rise to an atoll, which could
not be distinguished from one formed during subsidence. I can, however,
hardly believe, in the former presence of as many banks (there having been
no subsidence) as there are atolls in the great oceans, within a reasonable
depth, on which minute oceanic organisms could have accumulated to the
thickness of many hundred feet. I think that it has been shown that the
oscillations from great waves extend down to a considerable depth, and if
so the oscillating water would tend to lift up (according to an old
doctrine propounded by Playfair) minute particles lying at the bottom, and
allow them to be slowly drifted away from the submarine bank by the
slightest current. Lastly, I cannot understand Mr. Murray, who admits that
small calcareous organisms are dissolved by the carbonic acid in the water
at great depths, and that coral reefs, etc., etc., are likewise dissolved
near the surface, but that this does not occur at intermediate depths,
where he believes that the minute oceanic calcareous organisms accumulate
until the bank reaches within the reef-building depth. But I suppose that
I must have misunderstood him.
Pray forgive me for troubling you at such a length, but it has occurred to
me that you might be disposed to give, after your wide experience, your
judgment. If I am wrong, the sooner I am knocked on the head and
annihilated so much the better. It still seems to me a marvellous thing
that there should not have been much and long-continued subsidence in the
beds of the great oceans. I wish that some doubly rich millionaire would
take it into his head to have borings made in some of the Pacific and
Indian atolls, and bring home cores for slicing from a depth of 500 or 600
feet. (535/4. In 1891 a Committee of the British Association was formed
for the investigation of an atoll by means of boring. The Royal Society
took up the scheme, and an expedition was sent to Funafuti, with Prof.
Sollas as leader. Another expedition left Sydney in 1897 under the
direction of Prof. Edgeworth David, and a deeper boring was made. The
Reports will be published in the "Philosophical Transactions," and will
contain Prof. David's notes upon the boring and the island generally, Dr.
Hinde's description of the microscopic structure of the cores and other
examinations of them, carried on at the Royal College of Science, South
Kensington. The boring reached a depth of 1114 feet; the cores were found
to consist entirely of reef-forming corals in situ and in fragments, with
foraminifera and calcareous algae; at the bottom there were no traces of
any other kind of rock. It seems, therefore, to us, that unless it can be
proved that reef-building corals began their work at depths of at least 180
fathoms--far below that hitherto assigned--the result gives the strongest
support to Darwin's theory of subsidence; the test which Darwin wished to
be applied has been fairly tried, and the verdict is entirely in his
favour.)
2.IX.V. CLEAVAGE AND FOLIATION, 1846-1856.
LETTER 536. TO D. SHARPE.
(536/1. The following eight letters were written at a time when the
subjects of cleavage and foliation were already occupying the minds of
several geologists, including Sharpe, Sorby, Rogers, Haughton, Phillips,
and Tyndall. The paper by Sharpe referred to was published in 1847
("Quart. Journ. Geol. Soc." Volume III.), and his ideas were amplified in
two later papers (ibid., Volume V., 1849, and "Phil. Trans." 1852).
Darwin's own views, based on his observations during the "Beagle"
expedition, had appeared in Chapter XIII. of "South America" (1846) and in
the "Manual of Scientific Enquiry" (1849), but are perhaps nowhere so
clearly expressed as in this correspondence. His most important
contribution to the question was in establishing the fact that foliation is
often a part of the same process as cleavage, and is in nowise necessarily
connected with planes of stratification. Herein he was opposed to Lyell
and the other geologists of the day, but time has made good his position.
The postscript to Letter 542 is especially interesting. We are indebted to
Mr. Harker, of St. John's College, for this note.)
Down, August 23rd [1846?].
I must just send one line to thank you for your note, and to say how
heartily glad I am that you stick to the cleavage and foliation question.
Nothing will ever convince me that it is not a noble subject of
investigation, which will lead some day to great views. I think it quite
extraordinary how little the subject seems to interest British geologists.
You will, I think live to see the importance of your paper recognised.
(536/2. Probably the paper "On Slaty Cleavage." "Quart. Journ. Geol.
Soc." Volume III., page 74, 1847.) I had always thought that Studer was
one of the few geologists who had taken a correct and enlarged view on the
subject.
LETTER 537. TO D. SHARPE.
Down [November 1846].
I have been much interested with your letter, and am delighted that you
have thought my few remarks worth attention. My observations on foliation
are more deserving confidence than those on cleavage; for during my first
year in clay-slate countries, I was quite unaware of there being any
marked difference between cleavage and stratification; I well remember my
astonishment at coming to the conclusion that they were totally different
actions, and my delight at subsequently reading Sedgwick's views (537/1.
"Remarks on the Structure of Large Mineral Masses, and especially on the
Chemical Changes produced in the Aggregation of Stratified Rocks during
different periods after their Deposition." "Trans. Geol. Soc." Volume
III., page 461, 1835. In the section of this paper dealing with cleavage
(page 469) Prof. Sedgwick lays stress on the fact that "the cleavage is in
no instance parallel to the true beds."); hence at that time I was only
just getting out of a mist with respect to cleavage-laminae dipping inwards
on mountain flanks. I have certainly often observed it--so often that I
thought myself justified in propounding it as usual. I might perhaps have
been in some degree prejudiced by Von Buch's remarks, for which in those
days I had a somewhat greater deference than I now have. The Mount at M.
Video (page 146 of my book (537/2. "Geol. Obs. S. America." page 146. The
mount is described as consisting of hornblendic slate; "the laminae of the
slate on the north and south side near the summit dip inwards.")) is
certainly an instance of the cleavage-laminae of a hornblendic schist
dipping inwards on both sides, for I examined this hill carefully with
compass in hand and notebook. I entirely admit, however, that a conclusion
drawn from striking a rough balance in one's mind is worth nothing compared
with the evidence drawn from one continuous line of section. I read
Studer's paper carefully, and drew the conclusion stated from it; but I may
very likely be in an error. I only state that I have frequently seen
cleavage-laminae dipping inwards on mountain sides; that I cannot give up,
but I daresay a general extension of the rule (as might justly be inferred
from the manner of my statement) would be quite erroneous. Von Buch's
statement is in his "Travels in Norway" (537/3. "Travels through Norway
and Lapland during the years 1806-8": London, 1813.); I have unfortunately
lost the reference, and it is a high crime, I confess, even to refer to an
opinion without a precise reference. If you never read these travels they
might be worth skimming, chiefly as an amusement; and if you like and will
send me a line by the general post of Monday or Tuesday, I will either send
it up with Hopkins on Wednesday, or bring it myself to the Geological
Society. I am very glad you are going to read Hopkins (537/4. "Researches
in Physical Geology," by W. Hopkins. "Phil. Trans. R. Soc." 1839, page
381; ibid, 1842, page 43, etc.); his views appear to me eminently worth
well comprehending; false views and language appear to me to be almost
universally held by geologists on the formation of fissures, dikes and
mountain chains. If you would have the patience, I should be glad if you
would read in my "Volcanic Islands" from page 65, or even pages 54 to 72--
viz., on the lamination of volcanic rocks; I may add that I sent the series
of specimens there described to Professor Forbes of Edinburgh, and he
thought they bore out my views.
There is a short extract from Prof. Rogers (537/5. "On Cleavage of Slate-
strata." "Edinburgh New Phil. Journ." Volume XLI., page 422, 1846.) in the
last "Edinburgh New Phil. Journal," well worth your attention, on the
cleavage of the Appalachian chain, and which seems far more uniform in the
direction of dip than in any case which I have met with; the Rogers
doctrine of the ridge being thrown up by great waves I believe is
monstrous; but the manner in which the ridges have been thrown over (as if
by a lateral force acting on one side on a higher level than on the other)
is very curious, and he now states that the cleavage is parallel to the
axis-planes of these thrown-over ridges. Your case of the limestone beds
to my mind is the greatest difficulty on any mechanical doctrine; though I
did not expect ever to find actual displacement, as seems to be proved by
your shell evidence. I am extremely glad you have taken up this most
interesting subject in such a philosophical spirit; I have no doubt you
will do much in it; Sedgwick let a fine opportunity slip away. I hope you
will get out another section like that in your letter; these are the real
things wanted.
LETTER 538. TO D. SHARPE.
Down, [January 1847].
I am very much obliged for the MS., which I return. I do not quite
understand from your note whether you have struck out all on this point in
your paper: I much hope not; if you have, allow me to urge on you to
append a note, briefly stating the facts, and that you omitted them in your
paper from the observations not being finished.
I am strongly tempted to suspect that the cleavage planes will be proved by
you to have slided a little over each other, and to have been planes of
incipient tearing, to use Forbes' expression in ice; it will in that case
be beautifully analogical with my laminated lavas, and these in composition
are intimately connected with the metamorphic schists.
The beds without cleavage between those with cleavage do not weigh quite so
heavily on me as on you. You remember, of course, Sedgwick's facts of
limestone, and mine of sandstone, breaking in the line of cleavage,
transversely to the planes of deposition. If you look at cleavage as I do,
as the result of chemical action or crystalline forces, super-induced in
certain places by their mechanical state of tension, then it is not
surprising that some rocks should yield more or less readily to the
crystalline forces.
I think I shall write to Prof. Forbes (538/1. Prof. D. Forbes.) of
Edinburgh, with whom I corresponded on my laminated volcanic rocks, to call
his early attention to your paper.
LETTER 539. TO D. SHARPE.
Down, October 16th [1851].
I am very much obliged to you for telling me the results of your foliaceous
tour, and I am glad you are drawing up an account for the Royal Society.
(539/1. "On the Arrangement of the Foliation and Cleavage of the Rocks of
the North of Scotland." "Phil. Trans. R. Soc." 1852, page 445, with Plates
XXIII. and XXIV.) I hope you will have a good illustration or map of the
waving line of junction of the slate and schist with uniformly directed
cleavage and foliation. It strikes me as crucial. I remember longing for
an opportunity to observe this point. All that I say is that when slate
and the metamorphic schists occur in the same neighbourhood, the cleavage
and foliation are uniform: of this I have seen many cases, but I have
never observed slate overlying mica-slate. I have, however, observed many
cases of glossy clay-slate included within mica-schist and gneiss. All
your other observations on the order, etc., seem very interesting. From
conversations with Lyell, etc., I recommend you to describe in a little
detail the nature of the metamorphic schists; especially whether there are
quasi-substrata of different varieties of mica-slate or gneiss, etc.; and
whether you traced such quasi beds into the cleavage slate. I have not the
least doubt of such facts occurring, from what I have seen (and described
at M. Video) of portions of fine chloritic schists being entangled in the
midst of a gneiss district. Have you had any opportunity of tracing a bed
of marble? This, I think, from reasons given at page 166 of my "S.
America," would be very interesting. (539/2. "I have never had an
opportunity of tracing, for any distance, along the line both of strike
and dip, the so-called beds in the metamorphic schists, but I strongly
suspect that they would not be found to extend, with the same character,
very far in the line either of their dip or strike. Hence I am led to
believe that most of the so-called beds are of the nature of complex folia,
and have not been separately deposited. Of course, this view cannot be
extended to THICK masses included in the metamorphic series, which are of
totally different composition from the adjoining schists, and which are
far-extended, as is sometimes the case with quartz and marble; these must
generally be of the nature of true strata" ("Geological Observations," page
166).) A suspicion has sometimes occurred to me (I remember more
especially when tracing the clay-slate at the Cape of Good Hope turning
into true gneiss) that possibly all the metamorphic schists necessarily
once existed as clay-slate, and that the foliation did not arise or take
its direction in the metamorphic schists, but resulted simply from the pre-
existing cleavage. The so-called beds in the metamorphic schists, so
unlike common cleavage laminae, seems the best, or at least one argument
against such a suspicion. Yet I think it is a point deserving your notice.
Have you thought at all over Rogers' Law, as he reiterates it, of cleavage
being parallel to his axes-planes of elevation?
If you know beforehand, will you tell me when your paper is read, for the
chance of my being able to attend? I very seldom leave home, as I find
perfect quietude suits my health best.
(PLATE: CHARLES DARWIN, Cir. 1854. Maull & Fox, photo. Walker &
Cockerell, ph. sc.)
LETTER 540. TO C. LYELL.
Down, January 10th, 1855.
I received your letter yesterday, but was unable to answer it, as I had to
go out at once on business of importance. I am very glad that you are
reconsidering the subject of foliation; I have just read over what I have
written on the subject, and admire it very much, and abide by it all.
(540/1. "Geological Observations on South America," Chapter VI., 1846.)
You will not readily believe how closely I attended to the subject, and in
how many and wide areas I verified my remarks. I see I have put pretty
strongly the mechanical view of origin; but I might even then, but was
afraid, have put my belief stronger. Unfortunately I have not D. Sharpe's
paper here to look over, but I think his chief points [are] (1) the
foliation forming great symmetrical curves, and (2) the proof from effects
of form of shell (540/2. This refers to the distortion of shells in
cleaved rocks.) of the mechanical action in cleaved rocks. The great
curvature would be, I think, a grand discovery of Sharpe's, but I confess
there is some want of minuteness in the statement of Sharpe which makes me
wish to see his facts confirmed. That the foliation and cleavage are parts
of curves I am quite prepared, from what I have seen, to believe; but the
simplicity and grandeur of Sharpe's curves rather stagger me. I feel
deeply convinced that when (and I and Sharpe have seen several most
striking and obvious examples) great neighbouring or alternating regions of
true metamorphic schists and clay-slate have their foliations and cleavage
parallel, there is no way of escaping the conclusion, that the layers of
pure quartz, feldspar, mica, chlorite, etc., etc., are due not to original
deposition, but to segregation; and this is I consider the point which I
have established. This is very odd, but I suspect that great metamorphic
areas are generally derived from the metamorphosis of clay-slate, and not
from alternating layers of ordinary sedimentary matter. I think you have
exactly put the chief difficulty in its strongest light--viz. what would be
the result of pure or nearly pure layers of very different mineralogical
composition being metamorphosed? I believe even such might be converted
into an ordinary varying mass of metamorphic schists. I am certain of the
correctness of my account of patches of chlorite schists enclosed in other
schist, and of enormous quartzose veins of segregation being absolutely
continuous and contemporaneous with the folia of quartz, and such, I think,
might be the result of the folia crossing a true stratum of quartz. I
think my description of the wonderful and beautiful laminated volcanic
rocks at Ascension would be worth your looking at. (540/3. "Geological
Observations on S. America," pages 166, 167; also "Geological Observations
on the Volcanic Islands," Chapter III. (Ascension), 1844.)
LETTER 541. TO C. LYELL.
Down, January 14th [1855].
We were yesterday and the day before house-hunting, so I could not answer
your letter. I hope we have succeeded in a house, after infinite trouble,
but am not sure, in York Place, Baker Street.
I do not doubt that I either read or heard from Sharpe about the Grampians;
otherwise from my own old suspicion I should not have inserted the passage
in the manual.
The laminated rocks at Ascension are described at page 54. (541/1.
"Volcanic Islands," page 54. "Singular laminated beds alternating with and
passing into obsidian.")
As far as my experience has gone, I should speak only of clay-slate being
associated with mica-slate, for when near the metamorphic schists I have
found stratification so gone that I should not dare to speak of them as
overlying them. With respect to the difficulty of beds of quartz and
marble, this has for years startled me, and I have longed (since I have
felt its force) to have some opportunity of testing this point, for without
you are sure that the beds of quartz dip, as well as strike, parallel to
the foliation, the case is only just like true strata of sandstone included
in clay-slate and striking parallel to the cleavage of the clay-slate, but
of course with different dip (excepting in those rare cases when cleavage
and stratification are parallel). Having this difficulty before my eyes, I
was much struck with MacCulloch's statement (page 166 of my "S. America")
about marble in the metamorphic series not forming true strata.
(FIGURE 6.)
Your expectation of the metamorphic schists sending veins into neighbouring
rocks is quite new to me; but I much doubt whether you have any right to
assume fluidity from almost any amount of molecular change. I have seen in
fine volcanic sandstone clear evidence of all the calcareous matter
travelling at least 4 1/2 feet in distance to concretions on either hand
(page 113 of "S. America") (541/2. "Some of these concretions (flattened
spherical concretions composed of hard calcareous sandstone, containing a
few shells, occurring in a bed of sandstone) were 4 feet in diameter, and
in a horizontal line 9 feet apart, showing that the calcareous matter must
have been drawn to the centres of attraction from a distance of four feet
and a half on both sides" ("Geological Observations on S. America," page
113).) I have not examined carefully, from not soon enough seeing all the
difficulties; but I believe, from what I have seen, that the folia in the
metamorphic schists (I do not here refer to the so-called beds) are not of
great length, but thin out, and are succeeded by others; and the notion I
have of the molecular movements is shown in the indistinct sketch herewith
sent [Figure 6]. The quartz of the strata might here move into the
position of the folia without much more movement of molecules than in the
formation of concretions. I further suspect in such cases as this, when
there is a great original abundance of quartz, that great branching
contemporaneous veins of segregation (as sometimes called) of quartz would
be formed. I can only thus understand the relation which exists between
the distorted foliation (not appearing due to injection) and the presence
of such great veins.
I believe some gneiss, as the gneiss-granite of Humboldt, has been as fluid
as granite, but I do not believe that this is usually the case, from the
frequent alternations of glossy clay and chlorite slates, which we cannot
suppose to have been melted.
I am far from wishing to doubt that true sedimentary strata have been
converted into metamorphic schists: all I can say is, that in the three or
four great regions, where I could ascertain the relations of the
metamorphic schists to the neighbouring cleaved rocks, it was impossible
(as it appeared to me) to admit that the foliation was due to aqueous
deposition. Now that you intend agitating the subject, it will soon be
cleared up.
LETTER 542. TO C. LYELL.
27, York Place, Baker Street [1855].
I have received your letter from Down, and I have been studying my S.
American book.
I ought to have stated [it] more clearly, but undoubtedly in W. Tierra del
Fuego, where clay-slate passes by alternation into a grand district of
mica-schist, and in the Chonos Islands and La Plata, where glossy slates
occur within the metamorphic schists, the foliation is parallel to the
cleavage--i.e. parallel in strike and dip; but here comes, I am sorry and
ashamed to say, a great hiatus in my reasoning. I have assumed that the
cleavage in these neighbouring or intercalated beds was (as in more distant
parts) distinct from stratification. If you choose to say that here the
cleavage was or might be parallel to true bedding, I cannot gainsay it, but
can only appeal to apparent similarity to the great areas of uniformity of
strike and high angle--all certainly unlike, as far as my experience goes,
to true stratification. I have long known how easily I overlook flaws in
my own reasoning, and this is a flagrant case. I have been amused to find,
for I had quite forgotten, how distinctly I give a suspicion (top of page
155) to the idea, before Sharpe, of cleavage (not foliation) being due to
the laminae forming parts of great curves. (542/1. "I suspect that the
varying and opposite dips (of the cleavage-planes) may possibly be
accounted for by the cleavage-laminae...being parts of large abrupt curves,
with their summits cut off and worn down" ("Geological Observations on S.
America," page 155). I well remember the fine section at the end of a
region where the cleavage (certainly cleavage) had been most uniform in
strike and most variable in dip.
I made with really great care (and in MS. in detail) observations on a case
which I believe is new, and bears on your view of metamorphosis (page 149,
at bottom). (Ibid., page 149.)
(FIGURE 7.)
In a clay-slate porphyry region, where certain thin sedimentary layers of
tuff had by self-attraction shortened themselves into little curling
pieces, and then again into crystals of feldspar of large size, and which
consequently were all strictly parallel, the series was perfect and
beautiful. Apparently also the rounded grains of quartz had in other parts
aggregated themselves into crystalline nodules of quartz. [Figure 7.]
I have not been able to get Sorby yet, but shall not probably have anything
to write on it. I am delighted you have taken up the subject, even if I am
utterly floored.
P.S.--I have a presentiment it will turn out that when clay-slate has been
metamorphosed the foliation in the resultant schist has been due generally
(if not, as I think, always) to the cleavage, and this to a certain degree
will "save my bacon" (please look at my saving clause, page 167) (542/2.
"As in some cases it appears that where a fissile rock has been exposed to
partial metamorphic action (for instance, from the irruption of granite)
the foliation has supervened on the already existing cleavage-planes; so,
perhaps in some instances, the foliation of a rock may have been determined
by the original planes of deposition or of oblique current laminae. I
have, however, myself never seen such a case, and I must maintain that in
most extensive metamorphic areas the foliation is the extreme result of
that process, of which cleavage is the first effect" (Ibid., page 167).),
but [with] other rocks than that, stratification has been the ruling agent,
the strike, but not the dip, being in such cases parallel to any adjoining
clay-slate. If this be so, pre-existing planes of division, we must
suppose on my view of the cause, determining the lines of crystallisation
and segregation, and not planes of division produced for the first time
during the act of crystallisation, as in volcanic rocks. If this should
ever be proved, I shall not look back with utter shame at my work.
LETTER 543. TO J.D. HOOKER.
Down, September 8th [1856].
I got your letter of the 1st this morning, and a real good man you have
been to write. Of all the things I ever heard, Mrs. Hooker's pedestrian
feats beat them. My brother is quite right in his comparison of "as strong
as a woman," as a type of strength. Your letter, after what you have seen
in the Himalayas, etc., gives me a wonderful idea of the beauty of the
Alps. How I wish I was one-half or one-quarter as strong as Mrs. Hooker:
but that is a vain hope. You must have had some very interesting work with
glaciers, etc. When will the glacier structure and motion ever be settled!
When reading Tyndall's paper it seemed to me that movement in the particles
must come into play in his own doctrine of pressure; for he expressly
states that if there be pressure on all sides, there is no lamination. I
suppose I cannot have understood him, for I should have inferred from this
that there must have been movement parallel to planes of pressure. (543/1.
Prof. Tyndall had published papers "On Glaciers," and "On some Physical
Properties of Ice" ("Proc. R. Inst." 1854-58) before the date of this
letter. In 1856 he wrote a paper entitled "Observations on 'The Theory of
the Origin of Slaty Cleavage,' by H.C. Sorby." "Phil. Mag." XII., 1856,
page 129.)
Sorby read a paper to the Brit. Assoc., and he comes to the conclusion that
gneiss, etc., may be metamorphosed cleavage or strata; and I think he
admits much chemical segregation along the planes of division. (543/2.
"On the Microscopical Structure of Mica-schist:" "Brit. Ass. Rep." 1856,
page 78. See also Letters 540-542.) I quite subscribe to this view, and
should have been sorry to have been so utterly wrong, as I should have been
if foliation was identical with stratification.
I have been nowhere and seen no one, and really have no news of any kind to
tell you. I have been working away as usual, floating plants in salt water
inter alia, and confound them, they all sink pretty soon, but at very
different rates. Working hard at pigeons, etc., etc. By the way, I have
been astonished at the differences in the skeletons of domestic rabbits. I
showed some of the points to Waterhouse, and asked him whether he could
pretend that they were not as great as between species, and he answered,
"They are a great deal more." How very odd that no zoologist should ever
have thought it worth while to look to the real structure of varieties...
2.IX.VI. AGE OF THE WORLD, 1868-1877.
LETTER 544. TO J. CROLL.
Down, September 19th, 1868.
I hope that you will allow me to thank you for sending me your papers in
the "Phil. Magazine." (544/1. Croll published several papers in the
"Philosophical Magazine" between 1864 and the date of this letter (1868).)
I have never, I think, in my life been so deeply interested by any
geological discussion. I now first begin to see what a million means, and
I feel quite ashamed of myself at the silly way in which I have spoken of
millions of years. I was formerly a great believer in the power of the sea
in denudation, and this was perhaps natural, as most of my geological work
was done near sea-coasts and on islands. But it is a consolation to me to
reflect that as soon as I read Mr. Whitaker's paper (544/2. "On Subaerial
Denudation," and "On Cliffs and Escarpments of the Chalk and Lower Tertiary
Beds," "Geol. Mag." Volume IV., page 447, 1867.) on the escarpments of
England, and Ramsay (544/3. "Quart. Journ. Geol. Soc." Volume XVIII., page
185, 1862. "On the Glacial Origin of certain Lakes in Switzerland, the
Black Forest, Great Britain, Sweden, North America, and elsewhere.') and
Jukes' papers (544/4. "Quart. Journ. Geol. Soc." Volume XVIII., page 378,
1862. "On the Mode of Formation of some River-Valleys in the South of
Ireland."), I gave up in my own mind the case; but I never fully realised
the truth until reading your papers just received. How often I have
speculated in vain on the origin of the valleys in the chalk platform round
this place, but now all is clear. I thank you cordially for having cleared
so much mist from before my eyes.
LETTER 545. TO T. MELLARD READE.
Down, February 9th, 1877.
I am much obliged for your kind note, and the present of your essay. I
have read it with great interest, and the results are certainly most
surprising. (545/1. Presidential Address delivered by T. Mellard Reade
before the Liverpool Geological Society ("Proc. Liverpool Geol. Soc."
Volume III., pt. iii., page 211, 1877). See also "Examination of a
Calculation of the Age of the Earth, based upon the hypothesis of the
Permanence of Oceans and Continents." "Geol. Mag." Volume X., page 309,
1883.) It appears to me almost monstrous that Professor Tait should say
that the duration of the world has not exceeded ten million years. (545/2.
"Lecture on Some Recent Advances in Physical Science," by P.G. Tait,
London, 1876.) The argument which seems the most weighty in favour of the
belief that no great number of millions of years have elapsed since the
world was inhabited by living creatures is the rate at which the
temperature of the crust increases, and I wish that I could see this
argument answered.
LETTER 546. TO J. CROLL.
Down, August 9th, 1877.
I am much obliged for your essay, which I have read with the greatest
interest. With respect to the geological part, I have long wished to see
the evidence collected on the time required for denudation, and you have
done it admirably. (546/1. In a paper "On the Tidal Retardation Argument
for the Age of the Earth" ("Brit. Assoc. Report," 1876, page 88), Croll
reverts to the influence of subaerial denudation in altering the form of
the earth as an objection to the argument from tidal retardation. He had
previously dealt with this subject in "Climate and Time," Chapter XX.,
London, 1875.) I wish some one would in a like spirit compare the
thickness of sedimentary rocks with the quickest estimated rate of
deposition by a large river, and other such evidence. Your main argument
with respect to the sun seems to me very striking.
My son George desires me to thank you for his copy, and to say how much he
has been interested by it.
2.IX.VII. GEOLOGICAL ACTION OF EARTHWORMS, 1880-1882.
"My whole soul is absorbed with worms just at present." (From a letter to
Sir W. Thistleton-Dyer, November 26th, 1880.)
LETTER 547. TO T.H. FARRER (Lord Farrer).
(547/1. The five following letters, written shortly before and after the
publication of "The Formation of Vegetable Mould through the Action of
Worms," 1881, deal with questions connected with Mr. Darwin's work on the
habits and geological action of earthworms.)
Down, October 20th, 1880.
What a man you are to do thoroughly whatever you undertake to do! The
supply of specimens has been magnificent, and I have worked at them for a
day and a half. I find a very few well-rounded grains of brick in the
castings from over the gravel walk, and plenty over the hole in the field,
and over the Roman floor. (547/2. See "The Formation of Vegetable Mould,"
1881, pages 178 et seq. The Roman remains formed part of a villa
discovered at Abinger, Surrey. Excavations were carried out, under Lord
Farrer's direction, in a field adjoining the ground in which the Roman
villa was first found, and extended observations were made by Lord Farrer,
which led Mr. Darwin to conclude that a large part of the fine vegetable
mould covering the floor of the villa had been brought up from below by
worms.) You have done me the greatest possible service by making me more
cautious than I should otherwise have been--viz., by sending me the rubbish
from the road itself; in this rubbish I find very many particles, rounded
(I suppose) by having been crushed, angles knocked off, and somewhat rolled
about. But not a few of the particles may have passed through the bodies
of worms during the years since the road was laid down. I still think that
the fragments are ground in the gizzards of worms, which always contain
bits of stone; but I must try and get more evidence. I have to-day started
a pot with worms in very fine soil, with sharp fragments of hard tiles laid
on the surface, and hope to see in the course of time whether any of those
become rounded. I do not think that more specimens from Abinger would aid
me...
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