in Darwin's case, innumerable
interruptions from sickness and other causes, and the oft-deferred hope
of reaching the end of his task were not the only causes operating to
make the work irksome. The great project, which was destined to become
the crowning achievement of his life, was now gradually assuming more
definite shape, and absorbing more of his time and energies.

Nevertheless, during all this period, Darwin so far regarded his
geological pursuits as his PROPER "work," that attention to other
matters was always spoken of by him as "indulging in idleness." If at
the end of this period the world had sustained the great misfortune of
losing Darwin by death before the age of forty--and several times that
event seemed only too probable--he might have been remembered only as
a very able geologist of most advanced views, and a traveller who had
written a scientific narrative of more than ordinary excellence!

The completion of the "Geology of the 'Beagle'" and the preparation of
a revised narrative of the voyage mark the termination of that 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 important 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. ("L.L." II. pages 247-48.)

But during these eight years of "species work," Darwin found
opportunities for not a few excursions int