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.