44 THE SOIL. III. 



would be benefited by the application of lime. In the case of 

 many limestone soils the actual inorganic matter in the soil 

 probably does not exceed 1 % of the amount of limestone 

 which must have been denuded in order to leave it. 



Transported soils. Many soils are produced from the decay 

 of rocks other than those upon which they rest. The rich 

 alluvial soils of wide valleys contain inorganic materials which 

 have been transported from a distance by the river and de- 

 posited there. The materials in many cases have been 

 brought from various rock formations, and the resulting soil 

 consequently possesses a greater fertility than would be shown 

 by a soil formed exclusively of the debris of any one kind of 

 rock. 



Other means of effecting transportation are provided by 

 glaciers. Large areas of land have, in many places, been 

 covered with a thick deposit of debris brought from a distant 

 source by moving ice. Such deposits are known as glacial 

 drift and often consist of a finely divided clay matrix holding 

 blocks of hard rock, which in some cases show the marks of 

 ice scratches and have been brought from an immense dis- 

 tance. 



Wind is sometimes a means of transporting matter from a 

 distance and depositing it so as to form a soil. This occurs 

 with sand near the sea coast or on the shores of large lakes, 

 and also, over greater distances, with the ashes ejected from 

 volcanoes. 



The formation of soils is mainly brought about by the fol- 

 lowing agencies : 



1. Water. This acts in various ways : 



(i.) Mechanically. The flow of water over a rock subjects 

 it to slight abrasion ; this is greatly increased by the 

 pebbles, stony fragments, &c., which are urged by 

 the current over its surface. In this way rapid 

 streams and rivers carry down large quantities of 

 materials from high ground and deposit them in the 

 low-lying plains, giving rise to alluvial deposits. 

 This action becomes most evident after heavy rains, 

 when the water becomes muddv and discoloured. 



