14 EARLY MAN IN BRITAIN. [CHAP. n. 



which took place in the Pleistocene age, 1 when the 

 Sahara Desert was covered by the sea, and a large part 

 of the Mediterranean area was dry land, or like that 

 now taking place in the Scandinavian peninsula, which is 

 being lifted up from the North Cape to Stockholm, and 

 depressed in the south, in Scania. 2 New conditions of 

 life were produced by these changes, so unfavourable for 

 the Secondary animals, that all the higher forms perished 

 that were unable to compete in the struggle for life 

 with the new invaders, whose presence marks the 

 Eocene period. The invasion of Europe by the placental 

 mammals is the great event which is the natural starting- 

 point for our enquiry into the ancient history of man, 

 since the conditions by which he was surrounded on his 

 arrival in Europe, form part of a continuous sequence of 

 changes, from that remote period down to the present 

 day. Each of these changes in life and geography will 

 be treated in outline in its due place in this work. 



The Eocene Classification. 



The Eocene period has been defined in the last 

 chapter as that in which the existing orders and families 

 of the placental mammalia appear for the first time. 

 The Eocene marsupials, however, are, as may be expected 

 from their class having appeared in the Secondary age, 

 in a far more advanced stage of evolution, being repre- 

 sented by a living genus, 3 the opossum, as well as by 



1 Chapter V. of this work ; Cave-hunting, 110. 



2 Lyell, Principles, 131. 



3 According to Gervais it belongs to an extinct genus Peratherium 

 (Zool. et Pal. Franc. , 4to). In this chapter, however, the views of Gaudry 

 are followed (Les Enchainements du Monde Animal}. 



