Note 13 — Chapter III · ASCENSION.

Dr. Daubeny (on Volcanoes, p. 180) seems to have been led to believe that certain trachytic formations of Ischia and of the Puy de Dôme, which closely resemble these of Ascension, were of sedimentary origin, chiefly from the frequent presence in them “of scoriform portions, different in colour from the matrix.” Dr. Daubeny adds, that on the other hand, Brocchi, and other eminent geologists, have considered these beds as earthy varieties of trachyte; he considers the subject deserving of further attention.