THE EUROPEAN SEAS. 



281 



may the arrangement of existing depressions suggest 

 reasons for the forms and relative positions of those 

 older areas of depression which have become effaced, 

 but which will be next described. 



The north polar depression is occupied by the 

 Arctic Ocean. The regular form of this basin is 

 well shown in the accompanying map ; with the 

 north polar axis as its central point, its shores — 

 both of Asia and Europe — nearly coincide with a 

 circle drawn between 71° and 72° north latitude. 



This is the seat of one of our primary zoological 

 provinces, the source of so many forms which at a 

 definite time spread southerly ; the great relative 

 magnitude of this province is well seen in the ac- 

 companying map. 



Physical features having an east and west direc- 

 tion can be traced through other portions of the 

 northern hemisphere. There is a broad zone of 

 depression between the 34th and 47th parallels of 

 north latitude, extending from 10° west to 90° east 

 of the meridian of London \ along this are found, 

 in continuous series, the Mediterranean, the Black 

 Sea, the Caspian, the Aral Sea, and the lake system 

 of Central Asia. There are several minor areas of 

 depression running parallel or concentrically with 

 these lines, such as that of 59° north latitude, along 

 which lies the Gulf of Finland, and which is con- 

 tinued from Stockholm eastwards through the 

 Swedish lakes. The north coast of Spain, dependent 

 on the elevation of the Pyrenean range, runs due 



