51 THE PROBLEMS OF THE DEEP SEA n 



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 con- 

 ditions were developed, the northern plants were 

 able to maintain themselves only on the bleak 

 heights, on which southern forms could not com- 

 pete with them. And, in like manner, Forbes sug- 

 gested 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 wanner waters of the 

 shallows. Thus depth in the sea corresponded in 

 its effect upon distribution to height on the 

 land. 



The same idea is applied to the explanation of 

 a similar anomaly in the Fauna of the ^gean : 



" In the deepest of the regions of depth of the Mgea.n, the 

 representation of a Northern Fauna is maintained, partly by 

 identical and partly by representative forms. . . . The presence 

 of the latter is essentially due to the law (of representation of 

 parallels of latitude by zones of depth), whilst that of the 

 former species depended on their transmission from their parent 

 seas during a former epoch, and subsequent isolation. That 



