In the course of repeated visits to Corsica I have been much struck by the extraordinary erosion, not only of cliffs, but even more so of detached masses or boulders, from near sea-level to heights of 5,000 to 6,000 feet; and, having taken some photographs last January of specimens of the kind last referred to, I sent them to my friend Professor Bonney, who informed me that he had never met with any instances of erosion of such a peculiar and unusual character, and asked whether I could furnish him with a fragment of the rock.