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, indeed1. 
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*.” 
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 
1L, L. 1. pp. 247—48. 2M. L.1. pp. 63, 64. 
