HOW THE SOIL WAS FORMED 55 



of similar material ground into coarse sand, and of still 

 finer material which is called soil. When the stream over- 

 flows, it sometimes forms a similar sand-bar in the lowlands 

 along its banks (Fig. 40). 



Plants aid in forming soil. At first nothing grows on 

 these sand-bars in the field, but soon a few plants attempt 



CToiM Tleteher's " RoVto.*' l>ono)eday. Page ft O>- 



FIG. 40. SHOWING HOW A RIVER FORMS SOIL ON THE INSIDE OF THE BEND 



to live there. When these decay they serve as fertilizers, so 

 that the next generation of plants is larger. After some 

 years this may become fertile soil. 



Tiny plants called mosses and lichens sometimes grow 

 on bare rock. The roots of these not only dissolve the 

 softer parts of the rock, but by their decay fertilize later 

 generations of higher plants, until in time a shallow soi) 

 is formed in the pockets in the surface of the rock. 



