Sciences Naturelles, 1829, p. 173; abstract in Proc. Geol. Soc. i. 140). In the autumn he left his companions and turned southward towards Naples. The times were rough, with Tripoli pirates still scouring the Mediterranean; but he made successful expeditions into Sicily, mule-riding and walking, and the evidences of recent elevation of the land and recent mountain-building confirmed him in his faith in the efficiency of existing causes. He saw that the relative ages of the later deposits could be determined by the proportion of living to extinct molluscan species which they contained; and to this we owe his division of the tertiary strata into eocene, miocene, and pliocene, which has met with world-wide acceptance (Principles of Geology, iii. 1833; a revised sketch of the observations of this period occurs in the preface to the 3rd edition, 1834). In opposition to the invocation, by Buckland and others, of numerous universal deluges, Lyell's studies in these volcanic areas taught him how fossiliferous deposits might have been slowly raised above the sea. The first volume of his book was published by Murray in January 1830, and its title was a summary of his work: ‘Principles of Geology: being an attempt to explain the former changes of the earth's surface, by reference to causes now in action.’ The second and third volumes appeared in 1832 and 1833 respectively, and the whole work was reprinted in four smaller volumes in 1834. This edition was styled the third, since the first and second volumes of the original edition had been reissued prior to the publication of the third. The sale of the book was remarkable from the outset, and it underwent constant revision from the author, appearing in one volume in 1853, and in its final two-volume form in 1867–8. The twelfth edition was issued in 1875. The ‘Principles’ practically gave the death-blow to the catastrophic school of geologists. By its support of George Poulett Scrope [q. v.] in questions relating to volcanos, it led to the acceptance of moderate views, even in respect of the more paroxysmic forces of the globe.
It was only natural, when these principles met with rapid, though not unquestioning acceptance (see, for instance, Sedgwick, Proc. Geol. Soc. i. 302–6), that contemporaries and later critics should point out that they were merely a revival of older theories. Dr. Fitton, in a very friendly spirit, regretted (Edinb. Review, lxix. 411) that James Hutton's advocacy of the same views was inadequately noticed by Lyell; Lyell replied that Steno (1669), Hooke (1705), and Moro (1740) deserved as much credit as Hutton, and that his earlier chapters dealt equally with all (Life, ii. 47). The nature of the evidence that Lyell adduced from fossiliferous deposits distinguished his position from that of all his predecessors; palæontology had arisen as a science between the date of Hutton's ‘Theory of the Earth’ (1785) and that of the ‘Principles,’ and Lyell, who spared no pains in consulting the conchologists, used the new weapon with a master-hand (see Geikie, memoir in Nature, xii. 325). The frank and uncompromising appeal to existing causes, to uniformity of action during vast geological periods, has made the doctrine of uniformitarianism in geology seem to some critics opposed to that of evolution; writing, however, to Scrope in 1830, Lyell says: ‘It is not the beginning I look for, but proofs of a progressive state of existence in the globe, the probability of which is proved by the analogy of changes in organic life’ (Life, i. 270). He did great service in substituting his views of the gradual extinction of species and the continuous creation of new ones for the catastrophes which even entered into the theories of Hutton, and which were supposed to sweep off whole faunas at a time; but he opposed Lamarck's theory of transmutation of species, until Charles Darwin and Mr. A. Russel Wallace brought forward evidence which seemed adequate to account for the evolution of higher from lower forms.
In 1830 Lyell visited Bordeaux and the Pyrenees, and was busy consulting Deshayes in Paris as to the species of his Sicilian shells. In 1831 the Archbishop of Canterbury, and the other governors of King's College, London, appointed him professor of geology in that institution. He never seems to have had much inclination for this work; but he gave one course in May and June 1832, and another in the spring of 1833. The attendance at this second course was much diminished through the exclusion of ladies by the governors; in this matter, as on most educational questions, Lyell was in advance of the general opinions of his day. His geological lectures were to some extent concerned with the Mosaic cosmogony, as well as with questions of actual observation, a combination necessitated by the temper of the times. He also gave seven lectures at the Royal Institution in 1832.
At Bonn, on 12 July 1832, he married Miss Mary Horner, daughter of Leonard Horner, whose name and influence are conspicuous in the early work of the Geological Society. In Miss Horner he found a most devoted and accomplished wife, and, owing to his weakness of sight, many of his letters were subsequently written in her hand. The two travelled together frequently on the con-
