112 ANNUAL REPORT OF NEW-YORK 



Marly soils (containing carbonate of lime) are especially prone 

 to fall to a fine powder during drying, since the carbonate of lime, 

 which like sand, shrinks very little, is itself in a state of extreme 

 division, and therefore more effectually se^^arates the clayey par- 

 ticles. The unequal shrinking of these two intimately mixed 

 ingredients, accomplishes a perfect pulverization of such soils. 

 Prof. Wolff, of the Academy of Agriculture, at Hohenheim, Wir- 

 temberg, states that on the cold heavy soils of Upper Lusatia, in 

 Germany, the application of lime has been attended with excel- 

 lent results, and he thinks that the larger share of the benefit is 

 to be accounted for, by the improvement in the texture of those 

 soils, which follows liming. The carbonate of lime is considerably 

 soluble in water charged with carbonic acid, as is the water of a 

 soil containing vegetable matter, and this agency of distribution 

 in connection with the mechanical operations of tillage, must in 

 a short time effect an intimate mixture of the lime with the 

 whole soil. A tenacious clay is thus by a heavy liming, made 

 to approach the condition of a friable marl. 



VI. The relations of the soil to heat are of the utmost impor- 

 tance in affecting its fertility. The distribution of plants in gene- 

 ral is determined by differences of mean temperature. In the 

 same climate and locality, however, we find the farmer distin- 

 guishing between cold and warm soils. 



The temperature of the soil varies to a certain depth with that 

 of the air; yet its changes occur more slowly, are confined to a 

 narrower range of temperature, and diminish downward in rapidity 

 and amount, until at a certain depth a point is reached wiiere the 

 temperature is invariable. 



In summer the temperature of the soil is higher in day time 

 than that of the air; at night the temperature of the surface 

 rapidly falls, especially when the sky is clear. 



In temperate climates, at a depth of three feet, the temperatm-e 

 remains unchanged from day to night; at a depth of 20 feet the 

 annual temperature varies but a degree or two; at 75 feet below 

 * the surface, the thermometer remains perfectly stationary. In the 

 vaults of the Paris Observatory, 80 feet deep, the temperature is 

 60^ Fahr. In tropical regions the point of nearly unvarying 

 temperature is reached at a depth of one foot. 



