EVIDENCES FROM GEOGRAPHIC DISTRIBUTION III 
tion there is an extensive bank under 1,000 fathoms, extending to and 
including Lord Howe’s Island, while north of this are other banks 
of the same depth, approaching towards a submarine extension of 
Queensland on the one hand, and New Caledonia on the other, and 
altogether suggestive of a land union with Australia at some very 
remote period. Now the peculiar relations of the New Zealand fauna 
and flora with those of Australia and of the tropical Pacific Islands to 
the northward indicate such a connection, probably during the Cre- 
taceous period; and here, again, we have the exceptional depth of the 
dividing sea and the form of the ocean bottom according well with the 
altogether exceptional isolation of New Zealand, an isolation which has 
been held by some naturalists to be great enough to justify its claim 
to be one of the primary Zoélogical Regions. 
THE DISTRIBUTION OF MARSUPIALS' 
A. R. WALLACE 
This singular and lowly organised type of mammals constitutes 
almost the sole representative of the class in Australia and New 
Guinea, while it is entirely unknown in Asia, Africa, or Europe. It 
reappears in America, where several species of opossums are found; 
and it was long thought necessary to postulate a direct southern con- 
nection of these distant countries, in order to account for this curious 
fact of distribution. When, however, we look to what is known of the 
geological history of the marsupials the difficulty vanishes. In the 
Upper Eocene deposits of Western Europe the remains of several 
animals closely allied to the American opossums have been found; 
and as, at this period, a very mild climate prevailed far up into the 
arctic regions, there is no difficulty in supposing that the ancestors of 
the group entered America from Europe or Northern Asia during early 
Tertiary times. 
But we must go much further back for the origin of the Australian 
marsupials. All the chief types of the higher mammalia were in 
existence in the Eocene, if not in the preceding Cretaceous period, 
and as we find none of these in Australia, that country must have been 
finally separated from the Asiatic continent during the Secondary or 
Mesozoic period. Now during that period, in the Upper and the 
Lower O@lite and in the still older Trias, the jaw-bones of numerous 
small mammalia have been found, forming eight distinct genera, which 
From A. R. Wallace, Darwinism (copyright 1889). Used by special per- 
mission of the publishers, The Macmillan Company. 
