INTRODUCTION, 5 
As the latter is still subsiding, there is accordingly evidence 
of a still further extension of the land in this direction at 
an earlier date. Wallace therefore concludes that Australia 
must be regarded as an ancient continent of the Secondary 
or early part of the Tertiary period, which is now gradually 
decreasing in size, this diminution being indicated by the 
gradual subsidence of New Caledonia and certain other South 
Pacific islands. 
Till quite recently it was likewise believed that there were 
no traces of Australian types of Marsupials in the Tertiary 
rocks of the New World. Of late years, however, there have 
been discovered in Patagonia a number of remains of large 
carnivorous Marsupials with teeth and jaws of the same 
general type as those of the Tasmanian Thylacine, and 
apparently belonging to the same group. If this eventually 
_ prove to be true, it would seem to point to there having 
been some kind of land connection between Australia and 
South America long after the period when the former country 
- was completely sundered from the rest of the Old World; 
| and it is noteworthy that there are certain other lines ot 
| evidence pointing to the same conclusion. Be this, however, 
_ as it may, it is certain that the Australian Marsupials, having 
| been isolated for countless ages from the rest of the world, 
| and thus not exposed to the competition of the higher types 
| of Mammalian life, have flourished and developed to an extent 
which they could not possibly have reached in any other part 
| of the world under existing conditions. Even there, how- 
| ever, their present state of development is nothing to what it 
| was during the Pleistocene or latest geological epoch, since 
| we find at that period evidence of the existence of giant 
| Kangaroos and Wombats (to say nothing of certain extinct 
forms which have left no living kindred), by the side of which 
| the largest existing species would appear almost dwarfs. ‘The 
