Distribution of Rivers. 59 



This law of the deposition of moisture, then, necessarily 

 regulates the existence of rivers, so that as a general rule 

 the number and size of these decrease from the equator to 

 the poles. 



Where local circumstances tend to increase or diminish 

 the fall of rain, we there find a corresponding effect produced 

 on the rivers. Thus the Torneo, a considerable stream in 

 North Lapland, though ranking but as a fifth or sixth rate 

 river, derives its origin in a very high latitude, about the 

 parallel of 69° north, and is perhaps the largest stream on 

 the earth's surface, to be found within this range of latitude. 

 It owes its origin to the unusual quantity of rain which falls 

 along the range of the Scandinavian Alps, and this unusual 

 deposition of moisture appears to be due to the influence of 

 the warm Gulf Stream which flows northwards along the 

 western base of the Norwegian mountains ; the annual fall 

 of rain here being on an average 82 inches. 



But besides this primary cause, which naturally arises from 

 the thermal condition of the earth's surface, there are secon- 

 dary and concurrent arrangements which mainly regulate 

 the existing distribution and diffusion of rivers, and these 

 arrangements will be found in the position of the principal 

 watersheds. 



In the continents of Asia and Europe there are two great 

 leading watersheds, — one, which may be called the northern, 

 extends from east to west in about the parallel of 50° to 55°. 

 In Asia, it consists of the high table-lands formed by the 

 Aldan, Altai, and Ural ranges of mountains. All the rivers 

 which flow north into the Arctic Ocean have their origins in 

 this great table land, as the Obi, Yenesei, Lena, Amoor, and 

 I others. A marked peculiarity in these rivers is, that their 

 tributaries take their rise in much the same parallel of lati- 

 i tude as the originals ; and that, as they flow northward 

 I through a comparatively rainless district, they are joined by 

 no affluents of any importance or permanency. This is very 

 different from the tropical rivers, — the Amazon, the Missis- 

 sippi, — and even the Danube, in a sub-tropical locality, which 

 continue to be supplied by ample tributaries onward to their 



