i6 



THE ORIGIN OF SOILS 



[chap. 



Scotland, the north of England, and Wales, these beds 

 are full of ice-scratched stones, and clearly represent 

 material that has been ground down by a moving 

 glacier : but the origin of the glacial drift of the eastern 

 counties is more obscure, for water seems to have played 

 some part in its formation. The beds are mostly stiff 

 and clayey in character, and by their included fragments 

 show from what formation, as a rule not very remote, 

 they have been derived. 



Rock-forming Minerals. 



In the solid crust of the earth D'Orbigny has 

 estimated that the chief minerals are present in the 

 following proportions — felspars, 48 per cent. ; quartz, 

 35 per cent. ; micas, 8 per cent. ; talc, 5 per cent. ; 

 carbonates of lime and magnesia, 1 per cent. ; 

 hornblende, augite, etc., 1 per cent; other minerals 

 and weathered products, 2 per cent. 



The following table shows the composition of these 

 chief minerals, with a few others that play some part in 

 the formation of soil : — 



