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C. DARWIN TO DR. TRITTEN.

Yesterday (and the previous days) I had some most interesting work in examining the marks left by extinct glaciers. I assure you, an extinct volcano could hardly leave more evident traces of its activity and vast powers.

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I found one with the lateral moraine quite perfect, which Dr. Buckland did not see. Pray if you have any communication with Dr. Buckland give him my warmest thanks for having guided me, through the published abstract of his memoir, to scenes, and made me understand them, which have given me more delight than I almost remember to have experienced since I first saw an extinct crater. The valley about here and the site of the inn at which I am now writing must once have been covered by at least 800 or 1,000 feet in thickness of solid ice! Eleven years ago I spent a whole day in the valley where yesterday everything but the ice of the glaciers was palpably clear to me, and I then saw nothing but plain water and bare rock. These glaciers have been grand agencies. I am the more pleased with what I have seen in North Wales, as it convinces me that my view of the distribution of the boulders on the South American plains, as effected by floating ice, is correct. I am also more convinced that the valleys of Glen Roy and the neighboring parts of Scotland have been occupied by arms of the sea, and very likely (for in that point I cannot, of course, doubt Agassiz and Buckland) by glaciers also.

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FROM CHARLES DARWIN.

DOWN, FARNBOROUGH, KENT,

June 15 [1850, probably].

MY DEAR SIR,—I have seldom been more deeply gratified than by receiving your most kind present of "Lake Superior." I had heard of it, and had much wished to read it, but I confess it was the very great honor of having in my possession a work with your autograph, as a presentation copy, that has given me such lively and sincere pleasure. I cordially thank you for it. I have begun to read it with uncommon interest, which I see will increase as I go on.

The Cirripedia, which you and Dr. Gould were so good as to send me, have proved of great service to me. The sessile species from Massachusetts consist of five species. . . . Of the genus Balanus, on the shores of Britain, we have one species (B. perforata Bruguière), which you have not in the United States, in the same way as you exclusively

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have B. eburneus. All the above species attain a somewhat larger average size on the shores of the United States than on those of Britain, but the specimens from the glacial beds of Uddevalla, Scotland, and Canada, are larger even than those of the United States.

Once again allow me to thank you with cordiality for the pleasure you have given me.

Believe me, with the highest respect, your truly obliged,

C. DARWIN.