Volume Ii Part 18 (1/2)
If I had written your Address (515/1. Address delivered by Lord Avebury as President of the British a.s.sociation at York in 1881. Dr. Hicks is mentioned as having cla.s.sed 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 x.x.xVII., 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 cla.s.s 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 pa.s.sage 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. a.s.soc. 1881, page 22): ”Prof. Ramsay divides lakes into three cla.s.ses: (1) Those which are due to irregular acc.u.mulations 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 cla.s.s 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 Shrops.h.i.+re 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 sh.e.l.ls. 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 grat.i.tude.”
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 G.o.d 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 d.i.c.k (517/4. ”Trans.
R. Soc. Edinb.” Volume IX., page 1, 1823.), in which the writers concluded that the roads were the sh.o.r.e-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 Aga.s.siz and Buckland (517/6. ”Edinb. New Phil. Journal,”
Volume x.x.xIII., 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. Aga.s.siz 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 sh.o.r.e-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 Aga.s.siz-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 d.i.c.k and of the glacial theory of Aga.s.siz, 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 sh.o.r.es 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 princ.i.p.al 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 b.u.t.tress-like acc.u.mulations of stratified s.h.i.+ngle 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.