FRESH-WATER STREAMS. 637 



greater also over the parts of continents within a few hundred miles 

 of the oceans than over those more distant, and over high mountains 

 than over the plains, as these are gathering places, owing to their 

 height and coldness. Further, America, considering its extent, is 

 much better supplied than Europe and Africa (p. 44). In the trop- 

 ics of the Old World the annual amount of precipitation is about 

 77 inches, while it is 155 inches in South America. In the Eastern 

 United States, it is 40 to 50 inches ; but west of the one hundredth 

 meridian, beyond the Mississippi to the Sierra Nevada, it is mostly 

 12 to 16 inches. The annual amount in Great Britain averages 35 

 inches ; France 20 to 21 ; the country, farther from the coast, in Cen- 

 tral Germany and Russia, only 15 to 20 inches ; but about the Alps, 

 it is mostly 35 to 50 inches. 



Of the water precipitated, the rivers seldom carry off one half, ex- 

 cept in regions of metamorphic rocks. In most parts of temperate 

 latitudes the amount is a third to two fifths of what falls ; the rest 

 disappears : (1) by evaporation ; (2) by becoming absorbed or subter- 

 ranean ; and (3) by being taken up by plants, animals, and mineral 

 oxidation. In warm latitudes, the amount is less, and may be under 

 one tenth. The annual discharge of the Mississippi River averages 

 nineteen and a half trillions (19,500,000,000,000) of cubic feet, vary- 

 ing from eleven trillions in dry years to twenty-seven trillions in 

 wet years. This amount is about one quarter of that furnished by 

 the rains. 



The Amazon, in the hot tropics, with a drainage area not twice as 

 large, carries to the sea Jive times as much water as the Mississippi. 



The mean annual discharge of the Missouri River is about three and three-quarter 

 trillions, or fifteen hundredths of the amount of the rains over the region. The corre- 

 sponding amount for the Ohio is five trillions, which is one quarter the amount of rain. 

 (Humphreys & Abbott.) The Ganges carries down about four and a half trillions an- 

 nually, and the Nile three and one fifth trillions. The rivers of England and Wales 

 carry to the sea 18.3 inches in depth out of an annual fall of ahout 32 inches. 



The distribution of the tributaries of a stream has much to do with 

 the supply of water received, as is illustrated by the Mississippi and 

 Amazon. The former river has its smaller eastern tributaries from 

 regions where the annual precipitation is 35 to 50 inches ; but its 

 northern and its far-reaching northwestern and western tributaries 

 come from where only 12 to 20 inches of rain fall in a year; more- 

 over, the flood-seasons for the two sets are nearly the same, that is, in 

 the spring and autumn. On the contrary, the Amazon, whose trunk 

 is near the equator, besides being in one of the rainiest parts of the 

 globe, has large tributaries, descending from regions north of the 

 equator, which are flooded from the great rains during the rainy sea- 



