l82 EVOLUTION, GENETICS AND EUGENICS 



tion there is an extensive bank under i,ooo 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 Zoological Regions. 



THE DISTRIBUTION OF UARSOPIAT^' 

 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 AustraUan 

 marsupials. AU 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 OoUte 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 i88q). Used by special per- 

 mission of the publishers, The Macmillan Company. 



