II THE PROBLEMS OF THE DEEP SEA 53 



tion of geological phenomena. Forbes connected 

 the two orders of inquiry still more closely ; and 

 in the thoughtful essay " On the connection be- 

 tween the distribution of the existing Fauna and 

 Flora of the British Isles, and the geological 

 changes which have affected their area, especially 

 during the epoch of the Northern drift," to which 

 reference has already been made, he put forth a 

 most pregnant suggestion. 



In certain parts of the sea bottom in the imme- 

 diate vicinity of the British Islands, as in the 

 Clyde district, among the Hebrides, in the Moray 

 Firth, and in the German Ocean, there are de- 

 pressed areae, forming a kind of submarine valleys, 

 the centres of which are from 80 to 100 fathoms, 

 or more, deep. These depressions are inhabited 

 by assemblages of marine animals, which ditfer 

 from those found over the adjacent and shallower 

 region, and resemble those which are met with 

 much farther north, on the Norwegian coast. 

 Forbes called these Scandinavian detachments 

 " Northern outliers." 



How did these isolated patches of a northern 

 population get into these deep places ? To 

 explain the mystery, Forbes called to mind the 

 fact that, in the epoch which immediately pre- 

 ceded the present, the climate was much colder 

 (whence the name of " glacial epoch " applied to 

 it); and that the shells which are found fossil, or 

 sub-fossil, in deposits of that age are precisely such 



