Combination of Geological and Biological Work 375 



period of fifteen years of Darwin's life during which geological studies 

 were his principal occupation. Henceforth, though his interest in 

 geological questions remained ever keen, biological problems engaged 

 more and more of his attention to the partial exclusion of geology. 



The eight years from October, 1846, to October, 1854, were 

 mainly devoted to the preparation of his two important monographs 

 on the recent and fossil Cirripedia. Apart from the value of his 

 description of the fossil forms, this work of Darwin's had an im- 

 portant influence on the progress of geological science. Up to that 

 time a practice had prevailed for the student of a particular 

 geological formation to take up the description of the plant and 

 animal remains in it often without having anything more than a 

 rudimentary knowledge of the living forms corresponding to them. 

 Darwin in his monograph gave a very admirable illustration of the 

 enormous advantage to be gained alike for biology and geology 

 by undertaking the study of the living and fossil forms of a natural 

 group of organisms in connection with one another. Of the advantage 

 of these eight years of work to Darwin himself, in preparing for the 

 great task lying before him, Huxley has expressed a very strong 

 opinion indeed 1 . 



But during these eight years of "species work," Darwin found 

 opportunities for not a few excursions into the field of geology. He 

 occasionally attended the Geological Society, and, as we have already 

 seen, read several papers there during this period. His friend, 

 Dr Hooker, then acting as botanist to the Geological Survey, was 

 engaged in studying the Carboniferous flora, and many discussions 

 on Palaeozoic plants and on the origin of coal took place at this 

 period. On this last subject he felt the deepest interest and told 

 Hooker, " I shall never rest easy in Down churchyard without the 

 problem be solved by some one before I die 2 ." 



As at all times, conversations and letters with Lyell on every 

 branch of geological science continued with unabated vigour, and in 

 spite of the absorbing character of the work on the Cirripedes, time 

 was found for all. In 1849 his friend Herschel induced him to supply 

 a chapter of forty pages on Geology to the Admiralty Manual of 

 Scientific Enquiry which he was editing. This is Darwin's single 

 contribution to books of an " educational " kind. It is remarkable 

 for its clearness and simplicity and attention to minute details. It 

 may be read by the student of Darwin's life with much interest, for 

 the directions he gives to an explorer are without doubt those which 

 he, as a self-taught geologist, proved to be serviceable during his life 

 on the Beagle. 



On the completion of the Cirripede volumes, in 1854, Darwin was 



1 L. L. n. pp. 24748. 2 M. L. I. pp. 63, 64. 



