64 AGRICULTURE. 



coal, are nearly the same, and rhombic those of 

 lime and marl. They powerfully attract and hold 

 moisture and carbonic acid, and they hasten the de- 

 composition of stable manures, or other vegetable 

 or animal product. Their action is most favourable 

 on wet and cold soils, and as a top-dressing to nat- 

 ural meadows and turnip crops. 



The practice of paring and burning the surface of 

 the earth has been much used, and warmly recom- 

 mended by the Irish ; and in their land of bogs, as 

 in the marshes of Holland, where infertility arises 

 from excess of vegetable matter, it may be useful ; 

 but to burn the surfaces of sandy, gravelly, or even 

 of dry clay soils, would be to lose sight of all sound 

 theory. 



Soils in general may be divided into two kinds, 

 sand and clay. The defect of the one is want of 

 cohesion between its parts ; that of the other, an 

 excessive or superabundant cohesion. But vegeta- 

 ble matter is, as we have seen, a remedy for both ; 

 and to accumulate this is the constant endeavour of 

 every enlightened agriculturist. Yet are we advi- 

 sed to destroy this vegetable matter by fire, and to 

 substitute for it a small portion of ashes, as more 

 favourable to vegetation than the soil itself! But 

 in what will these ashes differ from those found in 

 our chimneys, and of which enough may be had 1 

 In nothing, excepting that they may possess some- 

 what more alkaline salt ;* a circumstance which, if 

 the subsoil be not charged with oily and animal mat- 

 ter, will be more injurious than useful. 



* De Saussure's experiments prove, that the stems of trees 

 (other things being equal) produce less of this salt than the 

 branches, the branches less than the twigs, and the twigs less 

 than the leaves. M. Perthuys has formed a table of the relative 

 alkaline products of plants and trees. By this table it appears 

 that the leaves and stems of Indian corn give to the quintal eight 

 pounds thirteen ounces, those of oak one pound five ounces, and 

 those of pine five ounces. 



