THE WORK OF ROOTS 109 



erences you can in the crops borne by the different 

 kinds of soils in your region. Examine the different 

 soils with the microscope (as described above) : find 

 out all you can about their composition and method of 

 formation. 



How is soil formed ? Wherever there are rocks, soil 

 , is being formed. Most rocks tend to break up until 

 they are completely changed to soil. Among the 

 agencies which bring this about may be mentioned : 



(1) The mechanical action of moving water, ice and 

 wind; (2) changes of temperature; (3) the chemical 

 action of air and water; (4) the action of plants and 

 animals. Find out what you can about these agencies. 1 



Study the weathering of rocks in your vicinity, also 

 of building materials (including stone, brick, cement 

 and mortar) ; which kind of building material weathers 

 most rapidly? Why? On hillsides and mountains the 

 soil can be seen in the act of originating from the rock 

 which lies beneath it; such soil is said to be formed in 

 place. In valleys, on the other hand, we find soil 

 which has been transported from the hills or mountains 

 by ice (drift soils) or water (alluvial soils). Moving 

 water always carries some soil with it, and later on de- 

 posits it as the current slows down. This can be seen 

 in any stream or in the little rivulets which are formed 



1 Consult Bailey: "Principles of Agriculture," Chapter I; Johnson: "How" 

 Crops Feed," Chapter II; Gaye: "The Great World's Farm," Chapters I to VII; 

 King: "The Soil," Chapter I; any good text-book of Physical Geography; 

 Darwin: "The Formation of Vegetable Mould Through the Action of Worms." 



