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. 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. It continued to be a grief to Agassiz that Humboldt, the oldest of all his scientific friends, and the one whose opinion he most reverenced, still remained incredulous. Humboldt's letters show that Agassiz did not willingly renounce the hope of making him a convert. Agassiz's own letters to Humboldt are missing from this time onward. Overwhelmed with occupation, and more at his ease in his relations with the older scientific men, he had ceased to make the rough drafts in which his earlier correspondence is recorded. HUMBOLDT TO AGASSIZ. BERLIN, March 2, 1842.