COMPOSITION OF SOILS. 105 



There are virgin soils that now raise large crops, 

 but which will be soon exhausted, as their fertil- 

 izing ingredients are small in amount, though in 

 an active soluble state. Other soils, probably less 

 productive, contain an almost unlimited supply 

 of fertilizing ingredients, which are being gradu- 

 ally liberated and given in soluble form to supply 

 the wants of vegetation ; the former may become 

 sterile in less than twenty years, the latter be 

 productive for centuries. The facts just stated 

 show the importance of having soils analyzed, 

 so that the farmer may know the amount of 

 fertilizing substances he has on hand. This 

 would be analogous to taking an account of stock 

 by the merchant or manufacturer, only it need 

 not be done so often. After once acquiring this 

 knowledge, the farmer may easily estimate the 

 amount of various substances removed by 

 different crops, as well as what he has added in 

 the shape of manures, and so arrive at a know- 

 ledge of the true condition and real value of his 

 lands. Millions of dollars are expended annually 

 by farmers in substances not needed, solely from 

 the feet that they do not know what they 

 already possess or need, nor the constituents of 

 what they purchase. 



To illustrate this matter fully, we give analyses 

 of some fertile and sterile soils ; and as it has 

 been shown that all crops require silica, phos- 



