88 GEOLOGY. 



ly gather or take up more as they bend toward the equa- 

 tor, and are therefore drying winds. For this reason, 

 more rain falls on the eastern side of a continent than on 

 the western. The annual amount of rain in Europe is 

 32 inches, while in the temperate zone in the United 

 States, east of the Mississippi, it is 44 .inches, the differ- 

 ence being still greater if we compare the eastern part 

 of South America with the opposite side of the Atlantic 

 Ocean. You can see now what influence the mountains 

 have on fertility in the case of the American continent. 

 Its highest mountains are on the western side, and there- 

 fore the warm eastern winds sweep with their moisture 

 over almost the whole breadth of the continent, parting 

 with it here and there from condensing influences. Fer- 

 tility is the result of this diffusion over the continent of 

 this moisture, and hence America is appropriately called 

 by Professor Guyot the Forest Continent. Where the 

 moisture deposited from the passing wind is not enough 

 to produce forests, we have the prairies and the pampas. 

 Now if the low Appalachians were on the west and the 

 high Rocky Mountains were on the east of North Amer- 

 ica, most of the moisture of the trades would be con- 

 densed at once, and be poured back into the Atlantic 

 Ocean, and in that case the great river system of the 

 continent's basin would not exist, but in place thereof a 

 desert. You can readily apply for yourself the above ex- 

 planation to the desert of Sahara, in Africa, and other 

 great deserts, and therefore I need not dwell farther on 

 this interesting subject. 



168. Circulation of Water. Water is every where in 

 motion on the earth. Rising continually from every 

 point of the surface by being dissolved in the air, it is 

 brought down again to the earth by being condensed 

 from its vaporous state. There is, therefore, a constant 

 circulation of the water back and forth between the 

 earth and its envelope of air. In the earth itself it is 

 never at rest, but insinuates itself among all loose parti- 



