_Rise of Geology and Conformism._—Modern geology has its rise in James Hutton (1726–1797) of Edinburgh, Scotland. In 1785 and 1795, Hutton published his Theory of the Earth, with Proofs and Illustrations. His “immortal theory” is his only work on geology. “Fortunately for Hutton’s fame and for the onward march of geology, the philosopher numbered among his friends the illustrious mathematician and natural philosopher, John Playfair (1748–1819), who had been closely associated with him in his later years, and was intimately conversant with his geological opinions.” In 1802, Playfair published his Illustrations of the Huttonian Theory of the Earth, of which Geikie says, “Of this great classic it is impossible to speak too highly,” as it is at the basis of all modern geology. One of Hutton’s fundamental doctrines is that the earth is internally hot and that in the past large masses of molten material, the granites, have been intruded into the crust. It was these igneous views that led to his followers being called the Plutonists. Another of his great doctrines was that “the ruins of an earlier world lie beneath the secondary strata,” and that they are separated by what is now known as unconformity. He clearly recognized a lost interval in the broken relation of the structures, and that the ruins, the detrital materials, of one world after another are superposed in the structure of the earth. Hutton also held that the deformation of once horizontally deposited strata was probably brought about at different periods by great convulsions that shook the very foundations of the earth. After a convulsion, there was a long time of erosion, represented by the unconformity. Geikie says, “The whole of the modern doctrine of earth sculpture is to be found in the Huttonian theory.” The Lyellian doctrine of metamorphism had its origin in Hutton, for he showed that invading igneous granite had altered, through its heat and expanding power, the originally waterlaid sediments, and that the schists of the Alps had been born of the sea like other stratified rocks. Hutton is the father of the Uniformitarian principle, for he “started with the grand conception that the past history of our globe must be explained by what can be seen to be happening now, or to have happened only recently. The dominant idea in his philosophy is that the present is the key to the past.” This principle has been impressed on all later geologists by Sir Charles Lyell, and is the chief cornerstone of modern geology.