I SO HISTORY OF THE EUROPEAN FAUNA. 



sisted of a broad expanse of ocean on which floated 

 numerous icebergs, which originated from the Scan- 

 dinavian glaciers as they reached the sea. This was 

 a cold sea, whilst Western Scandinavia was washed 

 by the Gulf Stream (vide Fig. 12, p. 156). We 

 might look upon the boulder-clay which covers such 

 vast tracts of country in Northern Germany, Russia, 

 and Holland as deposits formed by this sea rather 

 than the ground-moraine of a huge Scandinavian 

 glacier. I shall refer to this subject again in the 

 next chapter ; meanwhile it may be remembered 

 that the boulder-clay of Northern Europe exactly 

 resembles in all important particulars the similar 

 accumulations met with in the British Islands. 

 They resemble one another also in the occasional 

 occurrence of sea-shells, the frequent appearance of 

 bedded deposits, and the often inexplicable course 

 taken by boulders from their source of origin. There 

 occurs often a singular mixture and an apparent 

 crossing of the paths of boulders in the boulder- 

 clay. Professor Bonney remarks (p. 280) that these 

 are less difficult to explain on the hypothesis of 

 distribution by floating ice than on that of transport 

 by land-ice, because, in the former case, though the 

 drift of winds and currents would be generally in one 

 direction, both might be varied at particular seasons. 

 So far as concerns the distribution and thickness of 

 the glacial deposits, he says there is not much 

 to choose between either hypothesis; but on that 

 of land-ice it is extremely difficult to explain the 



