Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/45

 Rh once been in a fluid, or even a nebular state, from the presence of intense heat, the passage of the first consolidated portions of this fluid, or nebulous matter, to a solid state may have been produced by the radiation of, heat from its surface into space; the gradual abstraction of such heat would allow the particles of matter to approximate and crystallize; and the first result of this crystal ligation might have been the formation of a shell or crust, composed of oxidated metals and metalloids, constituting various rocks of the granitic series, around an incandescent nucleus, of melted matter, heavier than granite; such as forms the more weighty substance of basalt and compact lava.

It is now unnecessary to dwell on controversies which have prevailed during the last half century, respecting the origin of this large and important class of unstratified crystalline rocks, which the common consent of nearly all modern geologists and chemists refers to the action of fire. The agency of central heat, and the admission of water to the metalloid bases of the earths and alkalis, offer two causes which, taken singly or conjointly, seem to explain the production and state of the mineral ingredients of these rocks; and to account for many of the grand mechanical movements that have affected the crust of the globe. The gradations are innumerable, wlflch connect the infinite varieties of granite, syenite, porphyry, greenstone, and basalt with the trachytic porphyries and lavas that are at this day ejected by volcanos. Although there still remain some difficulties to be explained, there is little doubt that the fluid condition in which all unstratified crystalline rocks originally existed, was owing to the solvent power of heat;