142 MIOCENE CLIMATE. 



the past. We have already shown (vol. ii. p. 92) that most of 

 the species of Mollusca of the Helvetian sea belong to the fauna 

 of the Mediterranean, and that many tropical but no exclusively 

 northern types occur among them ; and thus the Middle Miocene 

 fauna acquires a more southern aspect than that of the Medi- 

 terranean. Thus of the 147 Mollusca of the Helvetian stage 

 which are still found living, 20 (or about 14 per cent.) are at 

 present exclusively inhabitants of the tropics ; 38 species (or 

 26 per cent.) occur on the coasts of England, but almost all of 

 them are species which also live in the Lusitanian and Medi- 

 terranean zones, and therefore are not to be regarded as northern 

 forms; 120 species (or about 82 per cent.) still inhabit the 

 Mediterranean. Of the extinct species the majority represent 

 Mediterranean types, but many are connected with tropical 

 forms. It is consequently not in the latitude of Switzerland, 

 but in that of the Mediterranean that we meet with most of the 

 species of Mollusca agreeing with the species of the Swiss 

 Miocene ; and indeed, owing to the intermixture of tropical 

 forms, the majority rather belong to the southern than to the 

 northern coast of the Mediterranean. The same temperature 

 which now prevails in the North-African or Madeiran sea must 

 therefore have characterized the fourth stage of the Swiss Mio- 

 cene, immediately preceding the CEningian stage. 



We see, therefore, that the inhabitants of the land and of the 

 sea concur in giving the Swiss Miocene country a subtropical 

 character. This is not deduced from a few plants or animals, 

 but from an abundant fauna and flora, which lays before us an 

 entire series of the most multifarious phenomena, such as can 

 only be explained by the occurrence of such a climate. 



The same natural character is manifest in the Miocene flora 

 and fauna, not only of Switzerland, but of the whole of Central 

 Europe * ; the north of Europe, however, had a colder climate. 

 There was consequently even then a diminution of temperature 

 towards the north, but certainly in a much less degree than at 

 the present day. We see this even in the flora of the most 

 northern parts of Germany. In Samland (the old amber- 



* Prof. Heer has demonstrated this in his l Kecherches sur le Climat et la 

 V<%e"tation du pays Tertiaire.' 0. Gaudin's translation, pp. 66 et seqq. 



