HUTTON, JAMES (b. Edinburgh, Scotland, 3 June 1726; d. Edinburgh, 26 March 1797), geology, agriculture, physical sciences, philosophy.

    (1795). In this edition the 1788 theory is restated with no essential change in the first chapter of volume I. The remainder of the two volumes deals principally with the supporting proofs and illustrations. Only two of the four parts promised on the title page were published in 1795. Hutton left an unfinished manuscript containing six chapters totaling 267 pages, evidently intended for inclusion in an additional volume of the Theory. These chapters, published as volume III in 1899, are of considerable interest, for they contain accounts of several of his later geological journeys. A study of the three volumes reveals the remarkable extent of Hutton's geological knowledge, the thoroughness of his investigations, and the acuteness of his observations.

The methods Hutton had employed in forming his theory were essentially the same as those employed by modern field geologists. He examined many different types of rocks, paying attention to their structural relations one to another; and he considered in detail the mineralogical and chemical composition of individual rocks. He also studied intensively the physical processes now operating on the earth's surface. In addition he examined British, European, and American literature to find support for his conclusions.

The method he employed in formulating his theory was, as he claimed, based on the principles of natural philosophy. Some of his conclusions can be described as speculative, and others were based on misinterpreted evidence, but these elements in the theory do not destroy its validity as a whole. It could be argued that Hutton's theory incorporated ideas that he had gained from other authors. This question is difficult to answer, for although he had read extensively, he seldom if ever quotes the work of another author in a manner that suggests he had made use of his ideas. More often, references are made either to correct a particular author, or to confirm Hutton's own conclusions. His originality lies in the use he made of facts and ideas, not in their sources.

The most important advance in geological science embodied in Hutton's theory was his demonstration that the process of sedimentation is cyclical in operation, a principle now accepted as axiomatic. Hutton's cycle involved the gradual degradation of the land surface by erosion; the transport of eroded matter to the sea, there to be deposited as sediments; and the consolidation of the sediments on the sea bottom, followed by their elevation to form new land surfaces, which in turn were subject to erosion. Hutton showed that this cyclic process must have been repeated an indeterminate number of times in the past, and because he could find no evidence to suggest that it might cease, he assumed that it would continue indefinitely.

In constructing his theory Hutton had used as a working hypothesis the assumption, based on his own observations, that the geological evidence provided by surface rocks provided both a key to the past and an indication of the probable future course of events. His theory formulated for the first time the general principle that some fifty years later came to be known as uniformitarianism.

In the fields of physical geology and geomorphology Hutton's views were strikingly modern. His knowledge of the processes of erosion and the agents that activate these processes, particularly river action, was thorough. His imaginative reasoning led to one remarkable conclusion about the possible action of glaciers in Switzerland. He had read in H. B. de Saussure's Voyages dans les Alpes (Neuchâtel, 1779) a description of scattered boulders of granite, often of immense size, which rested on limestone in the Saleve area, and had obviously been transported there from a distant source. De Saussure believed that their presence could not be accounted for by river action, and he suggested that they had been brought there by a vast debacle or general flood. Although he had not visited Switzerland, Hutton proposed a solution much nearer the truth. He suggested that in the past, when the height of the Alps had been very much greater, “immense valleys of ice sliding down in all directions towards the lower country, and carrying large blocks of granite to a great distance” (Theory, II [1795], 218), had transported these erratic blocks; and that in the course of time the upper parts of the mountains that had carried these glaciers had been removed by erosion. The true explanation, that the distribution of erratics of this sort had been effected by great ice sheets covering much of Europe, was not put forward until some forty years later.

Hutton also made contributions, second only in importance to his main theory, in the field of igneous geology. He was much impressed by the worldwide distribution of volcanic activity, and by the new discoveries that in some areas there occurred lavas that must have been erupted in prehistoric times. He made a detailed study of the numerous outcrops of igneous rocks in or near Edinburgh (some almost on his own doorstep), and of others in various parts of Scotland. He distinguished two types, lavas and intrusions, including among the latter both flat sheets and dykes, and he established for the first time the existence of a new class of rocks, the intrusive igneous rocks. He concluded that all igneous rocks originated in what he called the “mineral region,” a subcrustal zone of undefined depth in which heat of sufficient intensity to melt rocks prevailed.

Hutton also established the igneous origin of granite,