Hutton's imagination, on the basis of what can be observed to-day, pictured the chemical and mechanical disintegration of the rocks; and saw ice-streams bearing huge granite boulders from the declivities of primitive and more gigantic Alps. He believed (as Desmarest) that rivulets and rivers have constructed, and are constructing, their own valley systems, and that the denudation ever in progress would be eventually fatal to the sustenance of plant and animal and man, if the earth were not a renewable organism, in which repair is correlative with waste.
All strata are sedimentary, consolidated at the bottom of the sea by the pressure of the water and by subterranean heat. How are strata raised from the ocean bed? By the same subterranean force that helped consolidate them. The power of heat for the expansion of bodies, is, says Hutton (possibly having in mind the steam engine), so far as we know, unlimited. We see liquid stone pouring from the crater of a lofty volcano and casting huge rocks into mid-air, and yet find it difficult to believe that Vesuvius and Etna themselves have been formed by volcanic action. The interior of the planet may be a fluid mass, melted, but unchanged by the action of heat. The volcanoes are spiracles or safety-valves, and are widely distributed on the surface of the earth.
Hutton believed that basalt, and the whinstones generally, are of igneous origin. Moreover, he put granite in the same category, and believed it had been injected, as also metalliferous veins, in liquid state into the stratified rocks. If his supposition were correct, then granite would be found sending out veins from its large masses to pierce the stratified rocks and to crop out where stratum meets stratum. His conjecture was corroborated at Glen Tilt (and in the island of Arran). Hutton was so elated at the verification of his view that the Scotch guides thought he had struck gold, or silver at the very least. In the bed of the river Tilt he could see at six points within half a mile powerful veins of red granite piercing the black micaceous schist and giving every indication of having been intruded from beneath, with great violence, into the earlier formation.
Hutton felt confirmed in his view that in nature there is wisdom, system, and consistency. Even the volcano and earthquake, instead of being accidents, or arbitrary manifestations of divine wrath, are part of the economy of nature, and the best clue we have to the stupendous force necessary to heave up the strata, inject veins of metals and igneous rocks, and insure a succession of habitable worlds.