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.

Charles Darwin

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