Shall you do any levelling? I believe all the levelling has been [done] in Glen Roy, nearly parallel to the Great Glen of Scotland. For inequalities of elevation, the valley of the Spean, at right angles to the apparent axes of elevation, would be the one to examine. If you go to the head of Glen Roy, attend to the apparent shelf above the highest one in Glen Roy, lying on the south side of Loch Spey, and therefore beyond the watershed of Glen Roy. It would be a crucial case. I was too unwell on that day to examine it carefully, and I had no levelling instruments. Do these fragments coincide in level with Glen Gluoy shelf? MacCulloch talks of one in Glen Turret above the shelf. I could not see it. These would be important discoveries. But I will write no more, and pray your forgiveness for this long, ill-written outpouring. I am very glad you keep to your subject of the terraces. I have lately observed that you have one great authority (C. Prevost), [not] that authority signifies a [farthing?] on your side respecting your heretical and damnable doctrine of the ocean falling. You see I am orthodox to the burning pitch. LETTER 521. TO D. MILNE-HOME. Down, [September] 20th, [1847]. I am much obliged by your note. I returned from London on Saturday, and I found then your memoir (521/1. "On the Parallel Roads of Lochaber, with Remarks on the Change of Relative Levels of Sea and Land in Scotland, and on the Detrital Deposits in that Country," "Trans. R. Soc. Edinb." Volume XVI., page 395, 1849. [Read March 1st and April 5th, 1847.]), which I had not then received, owing to the porter having been out when I last sent to the Geological Society. I have read your paper with the greatest interest, and have been much struck with the novelty and importance of many of your facts. I beg to thank you for the courteous manner in which you combat me, and I plead quite guilty to your rebuke about demonstration. (521/2. Mr. Milne quotes a passage from Mr. Darwin's paper ("Phil. Trans. R. Soc." 1839, page 56), in which the latter speaks of the marine origin of the parallel roads of Lochaber as appearing to him as having been demonstrated. Mr. 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