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. The very fact that Australia incloses a large group of biggish quadrupeds, whose congeners once inhabited Europe and America, suffices in itself to prove beyond question that uninterrupted land communication must once have existed between Australia and those distant continents.