1172. Many soils are popularly distinguished as hot or cold, and the distinction appears in some measure founded upon fact. Some soils are much more heated by the rays of the sun (all other circumstances being equal) than others: and soils brought to the same degree of heat, cool in different times; i. e. some cool much faster than others. This property has been very little attended to in a philosophical point of view; yet it is of the highest importance in culture. In general, soils which consist principally of a stiff white clay, are with difficulty heated; and being usually very moist, they retain their heat but for a short time. Chalks are similar in one respect, - the difficulty with which they are neated; but, being drier, they retain their heat longer; less being consumed in causing the evaporation of their moisture. A black soil, containing much soft vegetable matter, is most heated by the sun and air; and the coloured soils, and the soils containing much carbonaceous or ferruginous matter, exposed under equal circumstances to the sun, acquire a much higher temperature than pale-coloured soils.
