DISTRIBUTION OF ARCTIC PLANTS. 347 



Norway many forms occur which are derived from the 

 British seas, and are even found as far south as the 

 Mediterranean. These serve greatly to swell the lists. 

 In fact the facies of the flora of Labrador is sub-arctic 

 and by no means purely arctic, as is that of Greenland. 

 Explained in this way the flora of Greenland seems to 

 us no more anomalous than its colder climate and re- 

 moteness from sub-arctic lands, isolated as it ever has 

 been by deep seas and powerful oceanic currents of dif- 

 ferent temperatures, which, we must believe, served 

 from very early times as barriers against the comming- 

 ling of more temperate forms of life with purely circum- 

 polar species. 



There is, in our view, no reason to believe that the 

 glacial period, as some writers have suggested, has 

 shifted from the eastern to the western hemisphere, or 

 vice versd ; for the same causes which brought on the 

 cold period were evidently common to the arctic and 

 sub-arctic regions throughout their whole extent, though 

 governed greatly by the present distribution of the iso- 

 thermal lines. That the drift deposits were laid down 

 contemporaneously on both sides of the Atlantic, seems 

 proved by' such facts as this : that Leda arctica (Z. port- 

 landicd), more than any other shell characteristic of the 

 drift deposits of the northern portions of America and 

 Europe, has become alike extinct both in Scandinavia 

 and its equivalent, Labrador, Canada, and New Eng- 

 land. 



The break in the glacial beds — which by Sars* (in 

 which he closely follows D'Archiac) are divided into an 



* Ora de i Norge forekommende fossile Dyrelevninger fra Quartaerperioden, 

 etc.; af M. Sars, Christiania, 1865. 



