THE PROBLEMS OF THE DEEP SEA. 4,59 



without bringing up a discovery. Even though the thing itself may 

 be neither " rich nor rare," the fact that it came from that depth, in 

 that particular latitude and longitude, will be a new fact in distribu- 

 tion, and, as such, have a certain importance. 



But it may be confidently assumed that the things brought up will 

 very frequently be zoological novelties ; or, better still, zoological an- 

 tiquities, which in the tranquil and little-changed depths of the ocean 

 have escaped the causes of destruction at work in the shallows, and 

 represent the predominant population of a past age. 



It has been seen that Audouin and Milne Edwards foresaw the gen- 

 eral influence of the study of distribution in depth upon the interpre- 

 tation of geological phenomena. Forbes connected the two orders of 

 inquiry still more closely ; and, in the thoughtful essay " On the Con- 

 nection between 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 sug- 

 gestion. 



In certain parts of the sea-bottom in the immediate vicinity of the 

 British Islands, as in the Clyde district, among the Hebrides, in the 

 Moray Firth, and in the German Ocean, there are depressed areoe, 

 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 differ 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 preceded the present, the 

 climate was much colder (whence the name of " glacial epoch " ap- 

 plied to it) ; and that the shells which are found fossil, or sub-fossil, in 

 deposits of that age are precisely such as are now to be met with only 

 in the Scandinavian or still more arctic regions. Undoubtedly, during 

 the glacial epoch, the general population of our seas had, universally, 

 the northern aspect which is now presented only by the " northern 

 outliers," just as the vegetation of the land, down to the sea-level, had 

 the northern character which is, at present, exhibited only by the 

 plants which live on the tops of our mountains. But, as the glacial 

 epoch passed away, and the present climatal conditions were developed, 

 the northern plants were able to maintain themselves only on the 

 bleak heights, on which southern forms could not compete with them. 

 And, in like manner, Forbes suggested that, after the glacial epoch, 

 the northern animals then inhabiting: the sea became restricted to the 

 deeps in which they could hold their own against invaders from the 

 south, better fitted than they to flourish in the warmer waters of the 



