22 AMERICAN AGRICULTURE. 



clown and enriching the loosened earth below ; and in time 

 this becomes good soil, which in proportion to its depth, 

 increases the area from which the roots derive their nutri- 

 ment. So manifest are the advantages which have followed 

 the use of subsoil plows, that they have been extensively 

 introduced of late years among the indispensable tools of 

 the better class of agriculturists. 



When the subsoil is loose and leecliy, consisting of an 

 excess of sand or gravel, thereby allowing the too ready 

 escape of moisture and the soluble portions of manures, the 

 subsoil plow is not only unnecessary, but positively injurious. 

 In this case the surface soil should be somewhat deepened by 

 the addition of vegetable manures, so as to afford a greater 

 depth, through which they must settle before they can get 

 beyond the reach of the roots ; and the supply of moisture 

 is thereby much augmented. It is better however, to keep 

 lands of this character in wood, or permanent pasture. 

 They are at best ungrateful soils, and make a poor return 

 lor the labor and manure bestowed upon them. 



If there be a diversity in the character of the sub and 

 surface soil, one being inclined to sand and gravel, and the 

 other to marl or clay, a great improvement will be secured 

 by allowing the plow to reach so far down as to bring up 

 and incorporate with the soil, some of the ingredients in 

 which it is wanting. This admixture is also of remarkable 

 benefit in old or long cultivated soils, which have become 

 deficient in inorganic matters and in their texture. 



The effect of long continued cultivation, besides exhausting 

 what is essential to the earthy part of plants, is to break 

 down the coarser particles of the soil, by the mechanical 

 action of the plow, harrow, dec., and in a much more rapid 

 degree, by the chemical combinations which cultivation and 

 manuring produce. A few years suffice to exhibit, striking ex- 

 amples in the formation and decomposition of rocks and stone*. 

 Stalactites and various specimens ot limestone, indurated 

 clays, sandstone and breccias or pudding stone.-, arc, formed 

 in favorable circumstances, almost under our eye ; while 

 some limestones, .shales, sandstones, &c., break down in larj;<; 

 masses annually, from the combined cfiect of moisture, heat 

 and frost. The same changes on a smaller scale, are con- 

 stantly going forward in the soil, and much more rapidly 

 while under cultivation. The general tendency of these 

 surface changes is towards pulverization. The particles 

 forming the soil, from the impalpable mite of dust, to the 



