OCEAXIC AND ATMOSPHERIC MOVEMENTS AND TEMPERATUEE. 51 



Atacania, and a dry shore region northward through Peru ; while the branch 

 going southward, which encounters increasing cold, makes one of the wetter 

 areas of the globe, Valdivia having an annual rainfall of 115 inches. The 

 same effects of the two branches are produced on the western border of 

 North America, the western border of north Africa and Europe ; in western 

 south Africa; in western Australia. (See Kainfall map by E. Loomis, 

 Amer. Jour. Sci., 111., xxiii., 1882.) 



On the contrary, the wind from the east over the tropics is a warm wind 

 charged with moisture. After striking North and South America it bends 

 away from the equator into cooler latitudes, and makes a great moist region 

 of eastern North America, and of eastern South America, with excessive 

 moisture over large areas ; and the position of the higher mountain range of 

 America, far toward the western border, lays open the whole interior to the 

 moisture. The trade winds produce a similar effect on the eastern side of 

 Eurasia and Australia, making the border of China one of the wet regions 

 of the globe, and so also a narrow mountain border for Australia. 



Mountains have cold summits, and consequently are great condensers of 

 moisture. They therefore take a prominent part in the above mentioned 

 system of results, and also produce local effects in other regions. 



The first high cold land struck by the winds takes a large portion of the 

 moisture out of them and leaves less, or little, for the region beyond. And 

 thus robbed, even the trades may become dry winds. The contrasts are well 

 shown on the opposite slopes of the Hawaiian mountains — the eastern 

 receiving much rain from the trades, the western getting almost none. For 

 the same reason the interior of North America is relatively dry, the amount 

 of precipitation over the Atlantic border being 40 to 50 inches a year, and 

 in the interior 20 to 40 and less. So it is also with the interior of South 

 America as compared with the coast region to the north ; and Sahara, begun 

 in northwestern Africa, stretches across the continent. The great Desert of 

 Gobi is thus shut off from sea winds, and winter winds blow from it instead 

 of into it. The higher ridges along the Rocky Mountain summit raise 

 locally the amount of precipitation, but it falls off again over all the western 

 slopes, and continues very small to the Sierra Nevada, averaging less than 

 10 inches a year over a broad belt from the Great Salt Lake region to the 

 Gulf of California. 



It is apparent from the facts which have been presented that the conti- 

 nents have derived many of their individualizing characteristics, their several 

 diversities of surface, climate, and life, from the disposing influence of the 

 earth's rotation. This is strikingly apparent in the existing flora and fauna, 

 briefly described in the following pages; it becomes still more evident after 

 a review of the succession of faunas and floras in the earth's history in 

 which the individual features of each continent are traced back far toward 

 "the beginning." 



The great truth is taught by the air and waters, as well as by the lands, 

 that the diversity about us, which seems endless and without order, is an 



