10 



THE QUANTITY OF SOIL SWEPT AWAY BY THE RAIN REPLACED BY 

 THE DECOMPOSITION OF THE ROCKS. 



Though the soil is thus continuously washed away, still it remains 

 nearly constant in quantity, since what is taken away by denudation 

 is made up from other causes, and this augmentation can proceed evi- 

 dently from nothing but the slow and constant disintegration of the 

 underlying rocks. The subsoils are likewise gradually being converted 

 into soil, and thus keep up the supply available for the nourishment of 

 plant life. The constant tillage and plowing of the ground subjects it 

 more readily to the weathering action than is the case with, grass or 

 other lands protected by natural vegetation.* 



THE GENERAL FERTILITY OF THE SOILS DEPENDS PRINCIPALLY ON 



THEIR TEXTURE. 



From an agricultural standpoint, the soil, which is the natural store- 

 house and laboratory from whence plants derive their supply of food, 

 should present different qualities which according as they are more 

 or less developed, exert a considerable influence upon its fertility ; it 

 should be firm enough to afford a proper degree of support for the 

 plants that grow on it, and yet loose enough to allow the delicate fibers 

 of the rootlets to extend themselves in all directions in search of the 

 food of which they are in need. It must be of such a texture as to al- 

 low the free access of air, without which plants cannot live; and it 

 must be close enough to retain, for a considerable time, the water which 

 falls on it, and yet porous enough to allow the excess to drain away. 

 In this respect, the nature of the subsoil and the depth of the surface 

 soil are both important. When a soil rests immediately upon a bed of 

 rocks or gravel, it will naturally be drier than when it rests on clay or 

 marl. On the other hand, a clay subsoil may be of great advantage 

 to a sandy soil, by enabling it to retain moisture longer in dry weather. 

 These qualities depend altogether on the state of division of the soil 

 and of its geological origin, and it is important, consequently, to study 

 the arable soil under the two standpoints of its physical properties and 

 of its chemical nature. (Peligqt.) 



THE PHYSICAL PROPERTIES OF SOILS. 



The physical properties of a soil may be considered in regard to its 

 texture, its absorbent powers, and its temperature. 



Soils differ not only in chemical composition, but also in physical 

 characteristics, the aspect, elevation, depth, climatic conditions, drain- 

 age, &c., that enter into the problem and cause the variations in the 

 relative productiveness of two fields. 



, The knowledge of the inherent agricultural capabilities of the differ- 

 ent classes of soil is still very far from being perfect, though, by the re- 



~ The Soil of the Farm. 



