Note 20 — Chapter III · ASCENSION.
Reading edition
In the section descriptive of St. Paul’s Rocks, I have described a glossy, pearly substance, which coats the rocks, and an allied stalactitical incrustation from Ascension, the crust of which resembles the enamel of teeth, but is hard enough to scratch plate-glass. Both these substances contain animal matter, and seem to have been derived from water in filtering through birds’ dung.