298 SOILS. 



ter case is that of Europe, where the prevailing westerly winds, 

 warmed by the Gulf Stream, temper the climate as far east as 

 the borders of Russia, and northward to Norway; while to 

 southward the warm waters of the Mediterranean and Black 

 seas temper both heat and cold in Spain, southern France, 

 Italy and the Mediterranean border generally. But to east- 

 ward, in Russia and Siberia, the climate becomes " conti- 

 nental ' to an extreme degree, with very cold winters and 

 very hot summers. The same is true of interior North Amer- 

 ica, wherever the continental divide cuts off the tempering in- 

 fluence of the westerly winds ; Montana, the Dakotas and the 

 Great Plains states generally being examples. The climate of 

 the Mississippi valley, as stated before, is tempered by the 

 winds blowing from the Gulf of Mexico, but with occasional 

 irruptions of the continental climate (sometimes reaching as 

 far east as the South Atlantic coast) in the forms of cold 

 " blizzards," from which the coast climates of the Pacific and 

 of western Europe are practically free. The Atlantic coast 

 of North America (including the coast of the Gulf of Mexico), 

 moreover, not unfrequently suffers from the violent cyclonic 

 storms that originate in the Antilles and follow more or less 

 the direction of the Gulf Stream. 



Islands, differing from continents mainly in their extent, 

 and having a relatively large proportion of coast, naturally 

 have climates controlled essentially by the surrounding ocean. 

 The insular or oceanic climates are therefore, as a rule, more 

 temperate and even than are those of the nearest mainland. 

 It is often said that the climate of western Europe is " in- 

 sular " ; and owing to its position under the lee of the Gulf 

 Stream, this is eminently true of Great Britain. 



Subtropic Arid Belts. Where the surface features of the 

 land in relation to the ocean and prevailing winds do not in- 

 terpose special obstacles, we find to poleward of both tropics 

 a climatic belt of greater or less width, in which the annual, 

 or at least the summer rainfall is too small to maintain annual 

 herbaceous vegetation throughout the season, even when the 

 temperature is favorable. These two " arid " belts are best 

 defined in Africa, where the northern one is represented by 

 the Sahara desert, lower Egypt and Arabia, while the south- 

 ern one is exemplified in the Kalahari desert, to northward of 



