My dear Lyell

Many thanks for sending me your most interesting correspondence.² What a capital man, Jamieson is! The letters came this morning & shall be forwarded tomorrow, which is the same as if posted by London Monday general post. I could not read them this morning for I was in middle of experiments on Dionæa, which could not be stopped.³

It is a grand subject you are discussing, & light must soon appear.— I wish I could help in the least, but I cannot. The absence of deltas on upper level of the Lochaber shelves seems to me quite sufficiently accounted for by small amount of land above the shelves on the lake or sea theory. Your argument of if submergence 1200 ft. in Perthshire since chief glacialisation, how about Glen Roy, is very striking.⁴ I have just been glancing at my Glen Roy paper;⁵ & there yet seem to me several points of very difficult explanation. (1) The levelled land-straits with terrace-like fringes above the level of the highest shelf. (2) the beds of pebbles on very gently inclined surface between Glen Turret & Glen Gluoy; & beds of pebbles on former islet (Meal Roy or Mealderry) at level of Lower shelf at the mouth of Glen Roy. When one sees what little power Glacial sea has to form pebbles, the case seems very odd in Glacial lake. (3) The fringe of detritus on sides of Spean & Roy valleys, about 60 ft thick all down the valley.; and buttresses of gravel on sides of Hills.— Is it possible that the river when it began to flow over the embankment of ice would cut its channel so slow & so drain the lake so slowly as to allow of all this great sloping accumulation? I remember perfectly well my surprise at vast contrast of state of valleys in N. Wales & Lochaber.⁶ But I suppose ice-lakes must be true cause.

What Jamieson says about climate not being icy if Scotland &c &c were all submerged 2000 or 3000 ft goes for nothing, when one thinks of Georgia in S. watery Hemisphere.—⁷ In former letter you speak of Scotland having been perhaps much loftier so as to account for great glaciers; this rubs against my notions, owing to the great extension & prevalence of Glacial phenomena. It always seems to me, until the contrary can be shown, to be safest to look at the great Glacial period as simultaneous.—

My dear Lyell | Yours most truly | C. Darwin

You quote Heer;⁸ I suppose that you know that Wollaston has overly bad opinion (all told me when at Torquay)⁹ of his Entomology & declares he is not to be at all trusted; & that Lowe says he has made great mistakes about Madeiran fossil plants.—¹⁰