GEOLOGICAL CLASSIFICATION OF SOILS 



39 



exhibits this isolated physical action to the greatest extent, 

 the particles being angular, coarse, and comparatively 

 fresh; farther down the slope the material may merge 

 by degrees into ordinary soil. Such soils are usually 

 shallow and stony, and approach the original rock in 

 color unless large amounts of organic matter have ac- 

 cumulated (Fig. 5). 



Fig. 5. — Diagram showing the formation of a colluvial soil, (a), bed 

 rock ; (6), dismantled cliff ; (d), coarse unproductive talus ; (p), soil 

 capable of bearing plants. 



29. Alluvial soils. — In considering the importance of 

 water as a weathering agent, it was found that it had 

 both cutting and transporting powers. The alluvial 



