ual mutations, and that during the course of
known geological time the continents and great oceans had again and
again changed places with each other. Sir Charles Lyell, in the last
edition of his _Principles of Geology_ (1872), said: "Continents,
therefore, although permanent for whole geological epochs, shift their
positions entirely in the course of ages;" and this may be said to have
been the orthodox opinion down to the very recent period when, by means
of deep-sea soundings, the nature of the ocean bottom was made known.
The first person to throw doubt on this view appears to have been the
veteran American geologist, Professor Dana. In 1849, in the Report of
Wilke's Exploring Expedition, he adduced the argument against a former
continent in the Pacific during the Tertiary period, from the absence of
all native quadrupeds. In 1856, in articles in the _American Journal_,
he discussed the development of the American continent, and argued for
its general permanence; and in his _Manual of Geology_ in 1863 and later
editions, the same views were more fully enforced and were latterly
applied to all continents. Darwin, in his _Journal of Researches_,
published in 1845, called attention to the fact that all the small
islands far from land in the Pacific, Indian, and Atlantic Oceans are
either of coralline or volcanic formation. He excepted, however, the
Seychelles and St. Paul's rocks; but the former have since been shown to
be no exception, as they consist entirely of coral rock; and although
Darwin himself spent a few hours on St. Paul's rocks on his outward
voyage in the _Beagle_, and believed he had found some portions of them
to be of a "cherty," and others of a "felspathic" nature, this also has
been shown to be erroneous, and the careful examination of the rocks by
the Abbe Renard clearly proves them to be wholly of volcanic
origin.[163] We have, therefore, at the present time, absolutely no
exception whatever to the remarkable fact that all the oceanic islands
of the globe are either of volcanic or coral formation; and there is,
further, good reason to believe that those of the latter class in every
case rest upon a volcanic foundation.

In his _Origin of Species_, Darwin further showed that no true oceanic
island had any native mammals or batrachia when first discovered, this
fact constituting the test of the class to which an island belongs;
whence he argued that none of them had ever been connected with
continen