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

    a rock hitherto classed as primeval and believed by geologists of the Wernerian school to have been deposited from water. His study of granite affords an instructive example of Hutton's acute powers of observation and reasoning and the fact that, in general, he did not reach conclusions without sound evidence to support them.

In his 1788 paper he mentioned that some of the rocks of the earth's crust are not stratified, in particular granite. He reserved judgment on the question of the origin of granite but claimed that if one species of granite could be shown to have existed in a state of fusion, then this conclusion could be extended to other varieties of the same rock. He described a particular, and quite abnormal, type of granite from Portsoy, in northeast Scotland, a specimen of which had been sent to him. He had not seen the outcrop but had been informed that it graded into granite of normal type.

This specimen (see Figure 1), illustrated in his 1788 paper, is clearly an example of the variety known as graphic granite, owing to a superficial resemblance to oriental writing evident when the rock is broken in a particular direction, perpendicular to the long axis of the contained quartz crystals which are embedded in a groundmass of feldspar. The quartz crystals then appear skeletal in form, with reentrant angles. Hutton concluded “it is not possible to conceive any other way in which these two substances, quartz and feld-spar, could thus be concreted, except by congelation [cooling] from a fluid state, in which they had been mixed” (“Theory” [1788], p. 256). That is to say the rock had cooled from a fused melt. This was a sound conclusion, for there is nothing in the appearance of the rock to suggest a sedimentary origin.

FIGURE 1. The specimen of graphic granite which led Hutton to conclude that granite is igneous in origin (Transactions of the Royal Society of Edinburgh, 1 [1788], plate II).

In a later paper, read to the Royal Society of Edinburgh in 1790, Hutton indicated that he had previously reserved judgment on the granite question as a whole, because he had not then decided whether granite

... was to be considered as a body which had been originally stratified by the collection of different [that is, sedimentary] materials, and afterwards consolidated by the fusion of these materials; or whether it were not rather a body transfused from the subterraneous regions, and made to break and invade the strata in the manner of our whinstone or trapp [“Observations on Granite,” in Transactions of the Royal Society of Edinburgh, 3 (1794), 77-78].

Hutton knew of the existence of foliated granite gneisses in Scotland, and he had read that such rocks were known to de Saussure in Switzerland, who had distinguished them from massive unfoliated granite. Hutton therefore suspended judgment until he had examined the margin of an outcrop of massive granite. This he did in the autumn of 1785 when visiting the duke of Atholl's estate at Glen Tilt, Perthshire. There Hutton found “the most perfect evidence, that granite had been made to break the Alpine strata, and invade that country in a fluid state. This corresponded perfectly with the conclusion which I had drawn from the singular specimen of the Portsoy granite” (ibid., 79-80). Hutton made journeys into other parts of Scotland where he obtained further confirmation of his conclusion. The school of geologists who accepted Hutton's ideas about the origin of igneous rocks came to be known as “plutonists,” a name first used by Kirwan.

While the thoroughness of Hutton's investigations and the ingenuity of his arguments are evident, some of his deductions and conclusions were unjustified. This was especially true in his discussions of the causes that he suggested were responsible for the consolidation and elevation of the strata. Here he was breaking new ground and attempting to solve problems that for the most part were insoluble at that time. He must have realized that if his theory was to be accepted, these problems could not be ignored. The solutions he reached were unduly influenced by the powers he attributed to the hot “mineral region” that he believed existed below both the continents and the oceans, powers for which he could produce little convincing evidence, although a source of heat was certainly present.

In discussing consolidation, although he did not consider seriously the possibility that compaction might have resulted from the pressure exerted by a thick mass of sediments, he did suggest that pressure could have driven the water out of porous rocks. Some