Revieios — Scharff's Origin of the Euro]jean Fauna. 479 



in Central Russia, between the Northern Sea and the greatly enlarged 

 Caspian, ceased to exist in the Interglacial phase, owing to the 

 gradual withdrawal of the Arctic waters from Northern Europe. 

 A slight refrigeration of the Siberian climate was the consequence, 

 and the barrier which prevented egress to Europe being now- 

 removed, the Northern Asiatic fauna swarmed across the plains 

 of the newly-opened continent. 



" During all this time, Scandinavia remained connected in the 

 north with Greenland, and in the south and west with Scotland and 

 Ireland, but it had no direct communication with the continent, 

 being separated from it by the North European sea. England and 

 France were united throughout the Glacial period, but the connection 

 between the former and Ireland broke down during, or shortly after, 

 the deposition of the Forest-bed, so that none of the Siberian 

 migrants, which now poured into England from the Continent, 

 reached Ireland." (p. 496.) 



'•It seems to me that the theory of the marine origin of the 

 Boulder-clay offers the following simple explanation : — After the 

 Interglacial phase of the Glacial period had passed away, a renewed 

 transgression of the Arctic waters must have occurred, but the sea 

 did not again invade Central Russia. As Professor J. Geikie has 

 pointed out, the erratics included in the Upper Boulder-clay of 

 Northern Continental Eui'ope have travelled in a different direction 

 from those contained in the Lower. A change of current, therefore, 

 evidently took place owing to the fact that the Northern European 

 sea was not now connected with the Ponto-Caspian basin. ^ 



" A large number of erratics would therefore be brought by 

 Scandinavian icebergs stranding on the east coast of England, 

 which was gradually being submerged by the advancing marine 

 transgression. As the water rose, the local glaciers which had 

 begun to form on the mountains of the North of England and 

 Scotland, cast off icebergs which scattered detritus and boulders 

 over the plain." (p. 497.) 



" I think the marine theory would explain in a more satisfactory 

 manner than the terrestrial one, the fact of the erratics being 

 carried in a direction contrary to the natural flow of a glacier, 

 if we remember that probably a strong current existed from the 

 more or less closed North European sea to the open Atlantic. 

 The occurrence in almost all the English Boulder-clays of marine 

 shells tells strongly in favour of the view that these clays are 

 of marine origin. Moreover, they are found to contain Arctic 

 species, and these are mixed with southern forms as we approach 

 the land adjoining the Atlantic, where an almost purely Mediter- 

 ranean fauna had hitherto existed. Arctic forms of life now found 

 their way, not only into the Atlantic, but by the newly-opened 

 Straits of Gibraltar they entered the Mediterranean, and are 

 preserved to us in some remarkable deposits in Sicily." (j). 500.) 



" I think Mr. Praeger's conclusions as to the changes in the 



^ This, again, is of great importance in establishing the contemporaneousness of 

 the Upper Continental Boulder- clay with the whole of the British clays. 



