More Letters of Charles Darwin Volume II

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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).)