THE FORMATION OF SOIL. 51 



of quartz, associated with, feldspar. Such soils 

 generally contain some compound of iron. 



Clayey soils are formed from the decomposition 

 of feldspathic rocks. They are impervious to 

 water and harden on drying. 



Calcareous soils contain carbonate of lime in 

 large amounts. 



Peaty soils are such as contain a large proportion 

 of partially decayed vegetable matter. 



The soil is sometimes found resting in place, 

 directly on top of the rocks from which it was 

 derived. In such cases its various mineral ingre- 

 dients can be traced directly to the decomposition 

 of the underlying rocks. 



A section of such rock and soil will show the 

 rock gradually passing from the loose soil into the 

 hard and unchanged rock. 



In other cases the soil is found at a considerable 

 distance from the locality in which it was originally 

 formed, or in which the plants grew that produced 

 its vegetable mould. 



The soil is carried from the rocks from which 

 its mineral ingredients were derived either by the 

 action of the winds or by the waters, though 

 mainly by the latter, to distances which often reach 

 thousands of miles. 



