GENESIS OF THE SOIL AND ITS POSSIBILITIES 177 



granitic soils. When formed chiefly from particles of 

 silex, they are called sandy soils. When consisting 

 mostly of silicate of alumina, they are called clay soils, 

 and so on." 



In addition to the above description there are several 

 points relating to the classification and nature of soils 

 which will prove of value and interest to the general 

 reader. These additional data are compiled chiefly 

 from my work on Agricultural Chemistry. 1 



" The weathering of rocks and their gradual disinte- 

 gration into the mineral bases of the soil is by many 

 considered to be largely influenced by the freezing and 

 thawing which are incidental to the change of seasons. 

 This is a plausible theory. The effect of freezing is 

 produced, as has already been intimated, by the expan- 

 sion which takes place when water reaches a tempera* 

 ture only a few degrees above the freezing point. As 

 the water is cooled to this point there is a gradual con- 

 traction of volume. At 4 centigrade, which is nearly 

 40 Fahrenheit, this contraction in the volume of 

 water, as it is further proved, stops, and an expansion 

 in volume takes place at lower temperatures. When 

 the water is crystallized into ice the maximum of ex- 

 pansion is secured. This crystallization, which seem- 

 ingly is produced by forces of a very minute character, 

 nevertheless goes on with almost irresistible force. 

 The strongest vessels are easily rent asunder by this 

 expansive force of freezing water. The well-known 

 phenomenon of bursting water pipes in cold weather is 

 an illustration of this herculean force. Apparently 

 man can construct no container strong enough to re- 

 sist it. 



i " Principles and Practice of Agricultural Analysis," Second 

 Edition, Volume I. Chemical Publishing Co., Easton, Pa. 



