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Mr.Horner and Sir David Brewster have described ("Philosophical Transactions" 1836 page 65) a singular "artificial substance resembling shell." It is deposited in fine, transparent, highly polished, brown-coloured laminae, possessing peculiar optical properties, on the inside of a vessel, in which cloth, first prepared with glue and then with lime, is made to revolve rapidly in water.

It is much softer, more transparent, and contains more animal matter, than the natural incrustation at Ascension; but we here again see the strong tendency which carbonate of lime and animal matter evince to form a solid substance allied to shell.) We found on St.Paul's only two kinds of birds--the booby and the noddy.

The former is a species of gannet, and the latter a tern.
Both are of a tame and stupid disposition, and are so unaccustomed to visitors, that I could have killed any number of them with my geological hammer.

The booby lays her eggs on the bare rock; but the tern makes a very simple nest with seaweed.