34 



THE FIRST BOOK OF FARMING 



particles from the water, and with them and their 

 bodies building beds of soil rich in organic matter 

 or humus. 



The sun, besides expanding and cracking the 

 rocks by its heat, helps in another way to make 

 soils. It warms the water that has been grinding 

 soil on the beach or along the river banks and 

 causes some of it to evaporate. This vapor rises, 

 forms a cloud and floats away in the air. By and 

 by the vapor forms into rain drops which may fall 

 on the top of some mountain. These rain drops 

 may wash loosened particles from the surface or 

 crevices of exposed rocks. These drops are joined 

 by others until, by and by, they form a little stream 

 which carries its small burden of rock dust down 

 the slope, now dropping some particles, now taking 

 up others. Other little streams join this one until 

 they form a brook which increases in size and power 

 as it descends the mountain side. As it grows by 

 the addition of other streams it picks up larger 

 pieces, grinds them together, grinds at its banks 

 and loads itself with rocks, pebbles, sand and clay. 

 As the stream reaches the lower part of the moun- 

 tain where the slope is less steep, it is checked in 

 its course and the larger stones and pebbles are 

 dropped while the sand and finer particles are car- 

 ried on and deposited on the bottom of some broad 

 quiet river farther down, and when the river over- 

 flows its banks, are distributed over the neighbor- 

 ing meadows, giving them a new coating of soil 

 and often adding to their fertility. What a river 



