io6 PROBLEMS OF EVOLUTION 



are in Eocene times, the first of the periods into which the Tertiary 

 is subdivided. With the Pliocene there is another advance. 

 There are the cave lion, the cave bear, the Irish Elk (Megaceros 

 hibernicus), and there is Man, All these advances have been 

 made by not very large stages, and each step in every group has 

 necessitated a levelling up in others, or extinction or retirement 

 to some sequestered corner. 



Back- Aldabra Island which lies north-west from Madagascar is one 

 " ers jj e of the quiet backwaters of life, unaffected by the onward sweep 

 of the main stream, and there the gigantic land-tortoise (Testudo 

 elephantina) has found refuge. Australia, for all its size, has 

 not been the scene of the fierce competition that has taken place 

 on continents, *and in it, as in a museum, have been preserved 

 very ancient Marsupials. How great the stress of the struggle 

 has been on continents is shown by the fact that the hippo- 

 potamus is the only mammal that survives to represent the fauna 

 of the Pliocene period. All the rest have been swept away or, 

 when the standard of life has risen and an age of higher pressure 

 has begun, have proved equal to the call upon them, and have 

 adapted themselves in structure and habit to the new order of 

 things. 



Plants Side by side with the development of animal forms has gone 

 on an upward movement in plant life. First, in the time of the 

 primary rocks, there are tree ferns and gigantic plants allied to 

 club mosses. With the secondary rocks come in conifers. Not 

 till the cretaceous deposits which mark the concluding phase of 

 the secondary period do we find deciduous trees, whose first 

 appearance, therefore, coincides with that of the Pterodactyls, 

 animal and vegetable life advancing together to higher planes. 

 The connection cannot be considered fanciful, for on plants, 

 directly or indirectly, animals depend for their food. The 

 deciduous trees belong to the higher orders of the phanerogams 

 (flowering plants), the characteristics of which are cross-fertilisa- 

 tion, rapid growth and variety of adaptation. Before their 

 advance ferns and club mosses have retreated to dark or hungry 

 corners. The lion's share of the sunlight and the soil is for the 

 modern enterprising phanerogams. 



