EARTHS AND SOILS. 37 



those which contain sand, finely-divided clay and lime, in 

 due proportions, and animal and vegetable matters. If 

 such soils are rendered permeable to the atmosphere, 

 which is always charged with the gaseous food of vegeta- 

 bles, by good tillage, and by the surface being kept clean 

 and loose, they are seldom affected by drought. Carbo- 

 nate of lime, and animal and vegetable matters, impart 

 to the soil this property, without increasing its tenacity, 

 A soil containing 11 parts of carbonate of lime, and 9 

 parts of vegetable matter, in 1000, when dried to 2120, 

 gained in an hour, by exposure to air, saturated with 

 moisture, at a temperature of 62"^, 18 grains ; 1000 parts 

 of fine sandy soil gained, under like circumstances, 11 

 grains ; and 1000 parts of coarse sand only 8 grains.* 

 Thus it would seem, that the power of a soil to absorb 

 moisture from the air, and with air other elements of fer- 

 tihty, depends, first, upon the presence of vegetable and 

 calcareous matters ; and, secondly, upon the soil being 

 well tilled, and the surface rendered permeable to the 

 atmosphere. 



The color of the soil has an influence upon the agency 

 of heat in inducing fertility, and consequently early matu- 

 rity of the crop. Several farm-crops, in our northeni 

 latitude, require a high temperature in the soil to bring 

 them to timely maturity. Such, particularly, are Indian 

 corn, and, in unfavorable seasons, the potato. White 

 soils, especially of clay, are heated with difficulty, owing 

 not only to color, but to compactness and retentiveness 

 of moisture. Such are truly denominated cold soils. 

 Black soils, abounding in vegetable matter, heat rapidly 

 under the sun's rays, and cool almost as rapidly when the 

 sun's rays are withdrawn. Sir H. Davy found that a 

 rich black mould, which contained nearly one fourth of 

 vegetable matter, had its temperature increased in an 

 hour, from 65° to 88°, by exposure to sunshine ; while a 

 white chalk soil was heated only to 69° under the same 

 circumstances. 



Now, as the soil supplies all our wants, and is, directly 



* Davy's Agricultural Chemistry. 



4 XV. 



