CLIMATE. 45 



The particular latitudes of western coasts most affected by the dry- 

 ing westerly winds — those between 28° and 32° — are generally ex- 

 cessively arid, and sometimes true deserts. 1 



The desert of Atacama, between Chili and Peru, the semi-desert of 

 California, the desert of Sahara, and the arid plains of Australia lie in 

 these latitudes. The aridity on the North American coast is felt even 

 beyond Oregon, through half the year. The snowy peak of Mount 

 St. Helen's, 12,000 feet high, in latitude 43°, stands for weeks together 

 without a cloud. The region of the Sacramento has rain ordinarily 

 only during three or four months of the year. 



As the first high lands struck by moist winds usually take away the 

 moisture, these winds afterward have little or none for the lands be- 

 yond. Here is the second great source of desert-regions. For this 

 reason, the region of the eastern Rocky Mountain slope, and the sum- 

 mits of these mountains, are dry and barren ; and, on the same prin- 

 ciple, an island like Hawaii has its wet side and its excessively dry 

 side. 



Under the influence of the two causes, the Sahara is continued in an 

 arid country across from Africa, over Arabia and Persia, to Mongolia 

 or the Desert of Gobi, in central Asia. 



It is well for America that her great mountains stand in the far 

 west, instead of on her eastern borders, to intercept the atmospheric 

 moisture and pour it immediately back into the ocean. The waters of 

 the great Gulf of Mexico (which has almost the area of the United 

 States east of the Mississippi) and those of the Mediterranean are a 

 provision against drought for the continents adjoining. It is bad for 

 Africa that her loftiest mountains are on her eastern border. 



It is thus seen that prairies, forest-regions, and deserts are located 

 by the winds and temperature in connection with the general configu- 

 ration of the land. 



The movements of the atmosphere and ocean's waters, and the sur- 

 face-arrangements of heat and cold, drought and moisture, sand-plains 

 and verdure, have a comprehensive disposing cause in the simple rota- 

 tion of the earth. Besides giving an east and west to the globe, and 

 zones from the poles to the equator, this rotation has made an east and 

 west to the atmospheric and oceanic movements, and thence to the 

 continents, causing the eastern borders of the oceans and land to differ 

 in various ways from the western, and producing corresponding pecu- 

 liarities over their broad surface. The continents, though in nearly 

 the same latitudes on the same sphere, have thence derived many of 

 those diversities of climate and surface which, through all epochs to 

 the present, have impressed on each an individual character, — an in- 

 1 W. C. Redfield, in Amer. Jour. ScL, xxv. 139, 1834, and xxxiii. 261, 1838. 



