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Rh on less novel ideas, also contained in the first volume of the Edinburgh 'Transactions,' was warmly attacked, especially by J. A. Deluc [q.v.], and led to a vigorous controversy. Hutton, after publishing his first sketch of the `Theory of the Earth,' visited several parts of Scotland, to test his views by crucial instances, one being the alternation of strata in close contact with granite in Glen Tilt, which he visited on the Duke of Athole's invitation in 1785 with his friend, John Clerk [q.v.] of Eldin. His exultation at finding his theory confirmed led his guides to think he must have discovered a vein of gold or silver. His observations on Glen Tilt were published in the third volume of the Edinburgh ‘Transactions.' In 1786 Galloway, in 1787 the Isle of Arran, in 1788 the Lammermuir Hills at St. Abb's Head, and the Isle of Man were visited, and all afforded proofs of the correctness of his views Hutton had also been busily pursuing other physical studies, and in 1792 published his 'Dissertations,' containing his papers on rain and climate, on phlogiston, and the laws of matter and motion. This was followed in 1794 by his ponderous 'Investigation of the Principles of Knowledge,' in 3 vols. 4to. His later years were occupied with the preparation of an elaborate work on 'The Elements of Agriculture,' which was never published. He died on 26 March 1797, in his seventy-first year. He was never married, but lived with three unmarried sisters, of whom only one, Isabella, survived him. She gave his collection of fossils to Dr. Black, who presented them to the Royal Society of Edinburgh. They cannot now be traced. Through his commercial connection with James Davie, Hutton died comparatively wealthy.

Hutton was slender, but active, thin-faced, with a high forehead, aquiline nose, keen and penetrating eyes, and a general expression of benevolence. His dress was very plain. His portrait was painted by Raeburn for John Davidson of Stewartfield. Upright, candid, humane, and a true friend, he was very cheerful in company, whether social or scientific, and was, like Adam Smith and Joseph Black, a leading member of the 'Oyster Club.' Playfair draws an interesting contrast (Biography of Hutton, pp.58,59) between Hutton and his friend Black, to whom, as well as to John Clerk of Eldin, he owed many valuable suggestions.

Hutton ranks as the first great British geologist, and the independent originator of the modern explanation of the phenomena of the earth's crust by means of changes still in progress. 'No powers,' he says, 'are to be employed that are not natural to the globe, no action to be admitted of except those of which we know the principle.' He first drew a marked line between geology and cosmogony. He early observed that a vast proportion of the present rocks are composed of materials afforded by the destruction of pre-existing materials. He realised that all the present rocks are decaying, and their materials being transported into the ocean; that new continents and tracts of land have been formed by elevation, often altered and consolidated by volcanic heat, and afterwards fractured and contorted; and that many masses of crystalline rocks are due to the injection of rocks among fractured strata in a molten state. His views on the excavation of valleys by denudation, after being largely ignored by Lyell, have been accepted and enforced by Ramsay, A. Geikie, and others. He may be considered as having originated the uniformitarian theory of geology (since modified by that of evolution). 'In the economy of the world,' he wrote, 'I can find no traces of a beginning, no prospect of an end.' The slowness of his; Theory of the Earth' to attract attention was due to its excessive condensation, its assumption of too great knowledge in the reader, its unexpected and abrupt transitions, and its occasional obscurity, which was by no means observable in Hutton's conversation. It was not till John Playfair published his classical 'Illustrations of the Huttonian Theory' (Edinburgh, 1802), that it received adequate attention.

Hutton's 'Theory of Rain' was a valuable contribution to science. He asserted that since the amount of moisture which the air can contain increases with the temperature, on the mixture of two masses of air of different temperatures part of the moisture must be condensed. He inferred that the rainfall in a locality is due to the humidity of the air and the intermingling of currents of air of different temperatures. Much of Hutton's physical work is obsolete, owing to his adoption of the phlogiston theory of heat and to his want of mathematical knowledge. His ‘Investigation of the Principles of Knowledge and of the Progress of Reason from Sense to Science,' occupying more than 2,200 quarto pages, is largely metaphysical, and has had little influence. He inclined to the Berkeleian view of the external world, arguing that there was no resemblance between our conception of the outer world and the reality, but maintaining that as our ideas of the external world are constant and consistent, our moral conduct is not affected by the difference. Hutton held that religion was evolved from barbarous cults, that monotheism was a revealed truth, that 