:14- LOCALITY AND FOREST VEGETATION. 



1. ()ri;iln of Soil. 

 All soil is origiiiiiUy the result of the disintegration of the 

 rocks of the earth, ^Yith the addition of certain organic sub- 

 stances. In some cases the soil now overlies the rock from 

 which it has been derived, in others it has been carried away 

 by violent convulsions, or the action of water and air currents, 

 and deposited again in other places. In the former case the 

 soil is called " indifie no ks,'' and in the latter " cov^u'." The 

 most important form of the latter is alluvial soil, formed b}' 

 deposits near the sea coast, in river deltas and inland by water 

 courses and lakes, as well as by the action of air currents. 



2. Formation of Indigenous Soil. 



The formation of soil is due to a variety of agencies, which 

 are either of a mechanical, chemical, or organic nature. 



a. Mi'cJianiml At/rncics. 



Amongst these, heat takes the foremost place. The heating 

 of rocks produces an unequal strain and pressure, which cause 

 them to burst in various directions. Then, if water penetrates 

 into the interstices and freezes, it forces the particles asunder, 

 thus further breaking up the rock. "Water is also a powerful 

 agency owing to its dissolving action. 



h. Clicmiral Afjcn'irs. 



Wlien oxygen and water, wliicli contains carbon dioxide 

 and other acids, come into contact with tlio rock, they form 

 chemical combinations with its elements. The oxygen acts 

 especially on the metals (as compounds of iron), forming, by 

 the addition of water, hydrates of metallic oxides. This 

 process, accompanied by an increase of volume, destroys the 

 previous cohesion of the rock. Water containing carbon 

 dioxide and other acids penetrates the rock, dissolves its 

 various constituents and carries off various substances, such 

 as \mo, miignc.sia and jiotash. 





