154 REPORT UF THE COMMISSIONER OF AGRICULTURE. 



remains iu motiou. When a river readies a flat or level tract and over 

 wiiidi its waters can flow in flood witli a slow motion, tlie sas])ended 

 matter, consisting principally of sand and mud, is deposited, and con- 

 stitutes the alluvium^ or new land, formed by such dei)osits at the river's 

 mouth or along its banks. 



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 evidently 

 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 suj>ply 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 pro- 

 tected 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 whence j^lants 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 root- 

 lets 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 allow the free ac- 

 cess 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 re- 

 spect, the nature of the subsoil and the depth of the surface soil arc 

 both important. When a soil rests immediately upon a bed of rocks or 

 gravel, it will naturally be dryer 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 its 

 geological origin, and it is im])ortant, consequently, to study the arable 

 soil under the two standpoints of its physical properties and of its chem- 

 ical nature. 



THE PHYSICAX PROPERTIES OF SOILS. 



The physical proi)orties of a soil may be considered in regard to its 

 texture, its absorbent i^owers, 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 agricultiu^al capabilities of the differ- 

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

 searches of chemists since 18G0, many important facts have been brought 

 to light which have led to improvements in the cultivation of the land. 



