22 THE SOIL OF THE FARM. 



These differences are the result of geological formation, 

 as well as of chemical composition. 



A proper mechanical texture in soils is also essential 

 to fertility. On the texture of a soil depends, not only 

 its suitableness for the growth of different crops, but like- 

 wise the rapidity of their growth. It is this also which 

 regulates, to a great extent, the soil's power of absorbing 

 and retaining heat, moisture, and manure. To be fertile, 

 the soil must be firm enough to afford a proper degree of 

 support to the plants which grow in it, and yet loose 

 enough to allow the delicate fibres of the rootlets to ex- 

 tend themselves in all directions. It must be of such a 

 texture as to allow 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 

 at the same time, 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 of them im- 

 portant. AYhen a soil rests immediatcl}^ upon a bed of 

 rock or gravel, it will be naturally drier than where the 

 subsoil is of clay and marl. On the other hand, a clay 

 subsoil may be of macerial advantage to a sandy soil, by 

 enabling it to retain moisture longer in dry weather. 



For the fertility of a soil depends not only on its com- 

 position — not only its wealth as a full storehouse of what 

 the growing plant needs as food, but on its efficiency as 

 a laboratory in which the materials thus required are 

 prepared for use. And it is in its relations to the water 

 which is the great carrier to and fro of the ingredients 

 which are at once the chemicals in this laboratory and 

 the food in this storehouse that the efficiency of a soil in 

 both these characters, and therefore its fertility, very 

 materially depends. Unless there be a sufficiently free 

 passage for the rain-water throughout the substance of 

 the soil, neither will the food of plants be properly pre- 



