PHYSICAL PROPERTIES OF SOIL. 219 



or calcareous — that is, 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. 



Sandy clay is — clay and sand, equal parts. 



Loamy clay is — 3-4 clay, and 1-4 sand. 



Peaty earth is — geine. 



Garden mould is — 8 per cent, geine. 



Arable land is — 3 per cent, geine. 



Taking these several varieties, it is found, that 

 sand is always the heaviest part of soil, whether dry 

 or wet ; clay is among the lightest part ; geine has 

 the least absolute weight, so that while a cubic foot 

 of sand weighs, in its common damp state, 141 lbs., 

 clay weighs 115 lbs., and geine 81 lbs.; hence gar- 

 den mould and arable soil weigh from 102 to 119 

 lbs. The more geine, compound soil contains, the 

 lighter it is. 



293. Among the most important physical charac- 

 ters of soil, is the power of retaining heat ; this will 

 be found to be nearly in proportion to its absolute 

 weight. The weight of soil, determines with tolera- 

 ble accuracy, its power of retaining heat. The 

 greater the mass in a given bulk, the greater is this 



