12 



AGRICULTURE 



LICHENS ON A ROCK 



wearing down the rocks, ice breaking them, frost crumbling them, 

 making the particles fine and ever finer. 



Fungi, Lichens, and Mosses. Even before the rocks were 

 ground and crumbled, there arose simple forms of vegetable life. 



fun'gi, H'chens, and mosses. 

 They drew some food from 

 the air, and dissolved and 

 absorbed other food from 

 the rock. Their decay add- 

 ed to the rock-dust the 

 material gathered from the 

 air. This formed soil. It 

 was poor and shallow at 

 first, able to nourish only 

 fungi, mosses, and other simple forms of life. 



But countless generations of low forms of plants and animals 

 deepened and enriched the soil. Higher and yet higher forms 

 succeeded. Untiringly, unrestingly, worked the forces of nature, 

 so slowly that at the end of a year or a century little advance 

 was visible, but so surely that the earth became a fair garden 

 spot, rich in vegetable and animal life. 



Classes of Soils. According to their origin, soils are divided 

 into two classes, sed'en ta ry and trans ported. 



Sedentary Soils. Sedentary soils, or soils in place, are those 

 that rest upon the rock from which they were formed. The soil 

 differs from the rock in being fine, loose, and porous, so as to 

 admit air, water, and roots. It is crumbled rock, subjected to 

 the action of plant and animal organisms and mixed with matter 

 formed by their decay. 



Transported Soils. But all soils do not rest upon the rocks 

 from which they were formed. Many have been transported, or 



