ths of 2,500 fathoms and upwards, which
renders it very improbable that there has ever been here a continuous land
surface, at all events during the Tertiary or Secondary periods of geology.

It is most interesting and satisfactory to find that this conclusion,
arrived at solely by a study of the form of the sea-bottom and the general
principle of oceanic permanence, is fully supported by the evidence of the
organic productions of the several islands; because it gives us confidence
in those principles, and helps to supply us with a practical demonstration
of them. We find that the entire group contains just that amount of Indian
forms which could well have passed from island to island; that many of
these forms are slightly modified species, indicating that the migration
occurred during late Tertiary times, while others are distinct genera,
indicating a more ancient connection; but in no one case do we find animals
which necessitate an actual land-connection, while the numerous Indian
types of mammalia, reptiles, birds, and insects, which must certainly have
passed over had there been such an actual land-connection, are totally
wanting. The one fact which has been supposed to require such a
connection--the distribution of the lemurs--can be far more naturally
explained by a general dispersion of the group from Europe, where we know
it existed in Eocene times; and such an explanation applies equally to the
affinity of the Insectivora of Madagascar and Cuba; the snakes
(Herpetodryas, &c.) of Madagascar and America; and the lizards
(Cryptoblepharus) of Mauritius and Australia. To suppose, in all these
cases, and in many others, a direct land-connection, is really absurd,
because {448} we have the evidence afforded by geology of wide differences
of distribution directly we pass beyond the most recent deposits; and when
we go back to Mesozoic--and still more to Palaeozoic--times, the majority
of the groups of animals and plants appear to have had a world-wide range.
A large number of our European Miocene genera of vertebrates were also
Indian or African, or even American; the South American Tertiary fauna
contained many European types; while many Mesozoic reptiles and mollusca
ranged from Europe and North America to Australia and New Zealand.

By very good evidence (the occurrence of wide areas of marine deposits of
Eocene age), geologists have established the fact that Africa was cut off
from Europe and Asia by an arm of the