ROCKS A GUIDE TO THE QUALITY OF THE SOIL. 129 



elements, and are practically inexhaustible of fertility. 

 Some of them have been under cultivation for 100 years, 

 and under ordinary fair treatment and a judicious rotation 

 of crops are now yielding as much as when first cleared of 

 the original forest more than 100 years ago. 



The practical conclusions to be derived from the preced- 

 ing considerations may be summed up as follows. 



First. Soils are derived either wholly or in part from the 

 rocks upon which they rest ; and when the soil is made up of 

 accumulations of drifted materials brought from a distance, 

 these are more or less mixed with materials derived from 

 the rocks upon which they lie. 



Second. That the condition of the rocky materials of the 1 

 soil may be made a guide as to the relation of the soil to> 

 the underlying rocks : for when these fragments are sharp 

 and angular, it proves that they have been derived from 

 adjacent sources and have not been transported any great 

 distance ; while the roundness and smoothness of the drift 

 indicate the more or less distant sources from which they 

 have been brought. 



Third. A knowledge of the composition of the rocks 

 from which any soil has been derived, enables the farmer 

 to form an accurate judgment of the quality and general 

 nature of the soil and becomes a safe guide to him as to the 

 details of its culture and management. 



Fourth. That as a result of the foregoing a study of the 

 outlines, at least, of the science of geology is of great import- 

 ance to the farmer and will be a most useful aid in the in- 

 telligent and successful culture of farm crops. 



