Note 3 — Chapter VI · TRACHYTE AND BASALT.—DISTRIBUTION OF VOLCANIC ISLES.

I have taken the specific gravities of the simple minerals from Von Kobell, one of the latest and best authorities, and of the rocks from various authorities. Obsidian, according to Phillips, is 2·35; and Jameson says it never exceeds 2·4; but a specimen from Ascension, weighed by myself, was 2·42.