Up to
the end of the time when the chalk deposits of Surrey, Kent, and Sussex
were laid down, indeed, there is no evidence of the existence anywhere
in the world of any mammals differing in type from those which now
inhabit Australia. In other words, so far as regards mammalian life, the
whole of the world had then already reached pretty nearly the same point
of evolution that poor Australia still sticks at.
About the beginning of the tertiary period, however, just after the
chalk was all deposited, and just before the comparatively modern clays
and sandstones of the London basin began to be laid down, an arm of the
sea broke up the connection which once subsisted between Australia and
the rest of the world, probably by a land bridge, _via_ Java, Sumatra,
the Malay peninsula, and Asia generally. 'But how do you know,' asks the
candid inquirer, 'that such a connection ever existed at all?' Simply
thus, most laudable investigator--because there are large land mammals
in Australia. Now, large land mammals do not swim across a broad ocean.
There are none in New Zealand, none in the Azores, none in Fiji, none in
Tahiti, none in Madeira, none in Teneriffe--none, in short, in any
oceanic island which never at any time formed part of a great continent.
How could there be, indeed? The mammals must necessarily have got there
from somewhere; and whenever we find islands like Britain, or Japan, or
Newfoundland, or Sicily, possessing large and abundant indigenous
quadrupeds, of the same general type as adjacent continents, we see at
once that the island must formerly have been a mere peninsula, like
Italy or Nova Scotia at the present day.
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