220 FIELD, FOREST AND FARM 



cultural operation is known as paring and burning, 

 and is carried out for the purpose of rendering 

 arable a tract of land not yet under cultivation and 

 still covered with wild vegetation. 



"The operation of paring and burning produces 

 two effects, one with reference to the clay in the 

 soil, the other having to do with the ashes left from 

 the burning of the weeds. Clay, as you know, is a 

 tenacious, binding substance, impervious to both 

 air and water. Consequently a soil that is too clayey 

 is unfavorable for vegetation, furnishing the roots 

 with insufficient air and moisture. Now, when clay 

 is heated to a high temperature, it acquires very 

 different properties: it no longer makes paste by 

 the addition of water, but is porous, permeable, and 

 readily admits air and water. The paring-and-burn- 

 ing process, therefore, improves an argillaceous soil 

 by calcining the clay and rendering it permeable. 

 That is as much as to say that if paring and burn- 

 ing are beneficial to heavy or clayey soils, they are, 

 on the other hand, harmful to those that are light 

 or sandy. 



"Finally, the operation just described affects the 

 soil through the ashes of the burnt weeds. After 

 the combustion of all vegetable matter there re- 

 mains an earthy powder or ash comprising the min- 

 eral substances contained in that vegetable matter, 

 substances unchanged by combustion because of their 

 great resistance to heat. The most important of 

 these is potash. All the ingredients that once be- 

 longed to the burnt plants are evidently adapted to 



