ScHARFF — On the Origin of the European Fauna. 467 



Europe shows, not ouly that it died out owing to the conditions in the 

 North European Ocean becoming unfavourable to its existence (no 

 doubt, owing to the sea growing more salt), but that the commu- 

 nication between the two seas ceased to exist, preventing further 

 migration. 



We can show clearly then, as pointed out before, tbat a land 

 passage was opened up between the shores of the receding Northern 

 Sea and those of the Ponto- Caspian, enabling the Siberian fauna to 

 enter Europe. 



On the accompanying map 6 are shown the probable geographical 

 conditions of Europe at this time. The land-surface, which separated 

 the Ponto-Caspian from the North European Sea, formed the bridge, 

 by means of which the Siberian migrants crossed over to Europe. 

 Long before this event took place, it had been a land- surface, but the 

 sea, as we have learned, had broken through it in several places, thus 

 forming an impassable barrier to the Siberian fauna. As the Northern 

 Sea retired during Intergiacial times, the bridge became passable again. 



The origin of this land-surface has long been a source of many 

 elaborate geological speculations. It occupies a vast region in Southern 

 Russia between the Carpathian Mountains and the Ural, and has a 

 world-wide fame, being known as the Black Earth of Russia, or 

 " Tchornosjem." Murchison (59) believed it to be a marine silt, 

 derived from the black Jurassic shale of Northern Russia. More 

 recently, after a careful chemical analysis, Mr. Ruprecht (73) demon- 

 strated that this black earth had been produced chiefly by the 

 decomposition of tufts of grass, no roots of trees or of bushes having 

 been found in it. "We may assume, therefore, that this tract of land, 

 over which the Siberian fauna wandered, consisted of a vast prairie. 

 On their arrival in the more central parts of Europe, the Siberian 

 Mammals spread into Austria, Hungary, and Northern Italy, through- 

 out the greater part of Germany and Prance, and into England (see 

 map, p. 448). They scarcely touched any part of Southern Europe, 

 and their progress in France was apparently arrested by the Garonne, 

 as no typical Siberian foims are found fossil south of that river in the 

 Pyrenees or in Spain. Of course, more recently the Siberian survivors 

 in Europe have spread not oialy into Southern Italy and Spain, but 

 also throughout Great Britain and Scandinavia. But, as previously 

 stated (p. 448), none of them entered Ireland, and I have given this as 

 one of my reasons for the belief that this country became separated 

 from England about the time when the Porest-bed was laid down, and 

 has never been since joined to it. 



