244 PHYSICAL PROPERTIES OF SOIL. 



Sandy clay is — clay and sand, equal parts. 

 Loamy clay is — f clay, and ^ 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 \s 

 always the heaviest part of soil, whether dry or wet; clay is 

 among the lightest parts ; geine has the least absolute weight, 

 so that while a cubic of sand weighs, in its common damp 

 state, 141 lbs., clay weighs 115 lbs., and geine 81 lbs. ; hence 

 garden 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 characters 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 tolerable accuracy, its power of retain- 

 ing heat. The greater the mass in a given bulk, the greater 

 is this power. Hence, sands retain heat longest, three times 

 longer than geine, and half as long again as clay. Hence, 

 the dryness and heat of sandy plains. Sand, clay, and peat, 

 are to each other as 1, 2, and 3 in their power of retaining 

 heat. But while the capacity of soil to retain heat, depends 

 on the absolute weight, the power to be warmed, another 

 very important physical character, depends on four principal 

 circumstances : first, the color ; second, the dampness ; third, 

 the materials ; fourth, the angle at which the sun's rays fall. 

 First, color ; the blacker the color, the easier warmed. 

 White sand and gray differ almost 50 per cent., in the 

 degree of heat acquired in a given time. As peat and the 

 varieties of geine are almost all of a black, or dark brown 

 color, it is seen how easily they may become warm soils,^ 

 when dry ; for secondly, dampness modifies the influence of 



