44 BRITISH PHYSICIANS. purpose, seemeth to me remarkable in chief, and doth give a clear testimony of the excessive multitude ; which is, that this island, as you ap- proach it, shineth with a white glazing, and the cliffs resemble mountains of the purest chalk, though the native complexion of the stone be obscure and black " That which thus discoloureth the island, is a white crust, which is friable, and of the very same consistence, complexion, and nature with the egg- shell f; so that all parts of the island are plastered over with this hard tegument, and crumbhng or friable crust or shell. The bottom of the island, which the tide washeth every day, retaining still its natural colour, clearly showeth that that fucus, or sophisticated whiteness, proceeds from the birds. None of these birds are citizens of the place, but foreigners all, and resort thither for convenient laying, and there they continue some weeks, as in an inn, till they and their young ones be all hi a condition to fly away together. But that white rough cast is so solid, firm, and thick, that you would think it were the genuine and natural sub- stance of the soil," &c. Soon after his return from Scotland, the anato- mical skill of Harvey was employed, by the king's command, in the dissection of that extraordinary
- The Bass Rock is principally composed of clink-stone, and be-
longs to the secondary trap rocks of the Wernerian. f According to chemists, egg-shells are composed of carbonate of lime and phosphate of lime, cemented by animal matter; and Vauquelin asserts, that the excreted matter, alluded to by Harvey, consists also of the same substances, together with the addition of a small quantity of silica. Assuredly, Harvey did not know this j but his natural sagacity made him suspect their identity.
