Note 2 — Chapter VI · TRACHYTE AND BASALT.—DISTRIBUTION OF VOLCANIC ISLES.
Reading edition
In a mass of molten iron, it is found (Edinburgh New Philosophical Journal, vol. xxiv, p. 66) that the substances, which have a closer affinity for oxygen than iron has, rise from the interior of the mass to the surface. But a similar cause can hardly apply to the separation of the crystals of these lava-streams. The cooling of the surface of lava seems, in some cases, to have affected its composition; for Dufrenoy (“Mém. pour servir,” tome iv, p. 271) found that the interior parts of a stream near Naples contained two-thirds of a mineral which was acted on by acids, whilst the surface consisted chiefly of a mineral unattackable by acids.