THE SOIL. 75 



from having been long cultivated, lias Ijeen more 

 opened to the influences of the air than is the case 

 with the subsoil, which has nevei" been disturbed so 

 as to allow the same action. Again the growth of 

 plants has supplied the surface soil with roots, which 

 by decaying have given it organic matter, thus dark- 

 ening its color, rendering it warmer, and giving it 

 greater ability to absorb heat and moisture, and to 

 retain manures. All of these effects render the sur- 

 face soil more fertile than it was before vegetable 

 growth commenced, unless, by the removal of crops, 

 its earthy plant-food has been too much reduced ; 

 and, where frequent cultivation and manures have 

 been applied, a still greater benefit has resulted. In 

 most instances the subsoil may, by the same means, 

 be gradually improved in condition until it equals 

 the surface soil in fertility. The means of produc- 

 ing this result, also further accounts of its advan- 

 tages, will be given under the head of Cultivation 

 (Sec. IV.). 



IMPEOVEMENT. 



From what has now been said of the charactex* of 

 the soil, it must be evident that, as we know the 

 causes of fertility and barrenness, we may by the 

 proper means inprove the character of all soils 

 which are not now in the highest state of fertility. 



Chemical analysis of the soil cannot give us any 

 reliable indication of its fertility or barrenness ; so 

 much depends on the state of solubility of the min- 

 eral plant-food, on the uniformity of its distribution 



