48 AMERICAN HUSBANDRY. 



tially exhausts, a specific food in the soil, suited to 

 its particular wants, we will not now stop to inquire ; 

 hut it. is a fact established by general experience, 

 that an annual change of crops upon a field, while 

 under tillage, tends very much to economize its fer- 

 tility, and to increase the profits of the labour be- 

 stowed upon it. Hence, 



19. It has been laid down as a sound rule in farm- 

 ing, that two white, or grain, or culmiferous crops 

 should not be made to succeed each other in the 

 same field ; but that each of these should be alterna- 

 ted with, or followed by, a green, a grass, a root, o." a 

 jeguminous crop. 



20. Where the soil of a farm will admit of it, a 

 good course is to alternate, 1, roots or Indian com, 

 with long manure., upon the sod ; 2, grain, with 

 grass-seeds ; 3, grass for two years. The poorer 

 the soil, the oftener should it be returned to grass, 

 particularly to clover and pasture. 



21. Geologists refer to three distinct formations 

 as constituting the crust of the earth : the primitive, 

 containing little or no lime or organic remains ; the 

 transition, containing lime and organic remains ; and 

 the secondary, abounding extensively in both these 

 elements of fertility. Their natural relative/er/i/i/y 

 is in the reverse order in which they are named, the 

 secondary being the best, and embracing most of the 

 great basin of the Mississippi, and the country drain- 

 ed by its tributary streams. We say nothing of 

 alluvial formations deposited by the ccean and 

 streams. These partake of the character of the 

 country from which they are brought, and are more 

 or less fertile, according to the fertility of the dis- 

 tricts from which their soil is derived, and the force 

 of the currents by which theii deposites have been 

 made ; a rapid current leaving only the coarser or 

 heavier materials, while the lighter and richer mat- 

 ters do not subside until the current becomes siow 

 and le?s agitated. A sluggish current, therHbre.de 

 posites the richest soil. 



