PHYSICAL PROPERTIES OF SOIL. 243 



culturist." Evidently, in the opinion of the authority quoted, 

 the composition and physical state of soils are independent 

 of each other ; and it may be thought that the author is ex- 

 ceeding the limits bounded by chemistry, when he touches 

 this new field, thus appropriated to the agriculturist. 



292. The physical characters of soil are embraced under 

 the terms, cold, hot, wet, and dry land. These characters 

 are dependent on four circumstances. 



Firstly, the absolute weight of a given bulk of soil, 



Secondly, its color, 



Thirdly, its consistency, 



Fourthly, its power of retaining water. 



In other words, the physical characters of soil may be con- 

 sidered under, 



Firstly, its relation to heat, 

 Secondly, its relation to moisture and gas, 

 Thirdly, its consistency, 

 Fourthly, its electrical relation. 



The relation to consistency makes soil light or heavy; 

 the relation to heat and moisture makes soil hot or cold, 

 dry or wet. The great natural varieties of soil are, sand, 

 clay, and loam ; first, the great distinction in the scale 

 of soil, is sand and clay : all intermediate varieties proceed 

 from mixtures of these, with each other. Now the sand 

 may be siliceous or calcareous, that is, composed of silicates, 

 the distinguishing character of soil in this country, or mixed 

 with a salt of lime, the feature of much European soil. By 

 clay is meant common blue clay, or sub-silicate of alumina, 

 consisting of alumina 36, silica, 68, oxide of iron, and salts 

 of lime, and alkalies, 6. 



