External Form, Structure, and Origin of Volcanic Mountains. — Cones and
Craters. — Hypothesis of “Elevation Craters” considered. — Trap Rocks.
— Name whence derived. — Minerals most abundant in Volcanic Rocks. —
Table of the Analysis of Minerals in the Volcanic and Hypogene Rocks. —
Similar Minerals in Meteorites. — Theory of Isomorphism. — Basaltic
Rocks. — Trachytic Rocks. — Special Forms of Structure. — The columnar
and globular Forms. — Trap Dikes and Veins. — Alteration of Rocks by
volcanic Dikes. — Conversion of Chalk into Marble. — Intrusion of Trap
between Strata. — Relation of trappean Rocks to the Products of active
Volcanoes.