706 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



compacted by water and acted upon by air, forms a suitable rooting place for 

 delicate mosses and other little plants, which live their short lives while the 

 moisture lasts on the shallow soil. This soil thus begun catches and holds the 

 blowing dust, the wear of the rocks, and incorporates into itself the vegetation 

 which grows and dies upon it. So it accumulates until it fills the crevices, 

 and loose stones are covered. Many plants thrive upon the ever deepening 

 eoil, and the hill-sides are finally covered. Shrubs and trees strike deep their 

 roots, drop their leaves, or dying, their whole substance becomes part and 

 parcel of the soil. Acted upon by the winds and rains the tendency of all 

 soils is to seek a level, and gradually find their way into the valleys and plains. 

 Soils are constantly forming, and moving as they do, rarely increase to much 

 extent save in the valleys, and here the tendency of that deeply buried is to 

 form a hard pan, the first step in the transformation of soil back again to rock. 

 This turning of soil to rock again is a natural result of heavy pressure, with 

 the percolating water bearing lime, iron, alkaline salts and silica among it, 

 thus hardening or cementing it together. Causes producing effects like these 

 have ever been going on, and all contribute to maintain the verdure and fer- 

 tility of the soil. 



Some of the volcanoes ailord us good opportunities for the study of soils, 

 and where at some former period the torrent of melted lava covered whole dis- 

 tricts, destroying all vegetation, leaving a thick crust of scoriae, sand and 

 ashes, or even solid rock, which within the historic period had been converted 

 into pasture fields, vineyards and even forests 



So extensive are the deposits of stones, gravel, sand, clay, &c., left there by 

 the agencies already alluded to, that it is a comparatively rare thing to find a 

 soil formed directly or chiefly from the rock upon which it lies. The most 

 common rocks, being usually mixtures of dilferent minerals, in their decomposi- 

 tion furnish soils, as a general thing, containing all the elements necessary for 

 the growth of agricultural plants. Trap rock consists chiefly of feldspar, and 

 hornblend, granite of feldspar, quartz and mica. None of these of necessity 

 contain sulphuric or phosphoric acid, without which no soil can be fertile. But 

 intimately mingled with these minerals, are found, in inconspicuous forms, 

 other minerals, viz : phosphates, sulphates, iron, manganese, etc., which are of 

 vital importance to the soil, so that in various ways the All-wise Father has 

 provided on the surface everywhere that the earthy essentials to fertility shall 

 not be wanting. Beside these mineral elements which give no evidence of 

 having been a part of either animal or vegetable organization, there are organic 

 elements, or that part of the soil which results from the decay of animal or 

 vegetable life, or has in some manner been produced by it. If a soil in the 

 condition of fine dry powder be put into an iron spoon and heated, it will 

 gmoke, turn dark -colored, and, perhaps, burn with flame. By this process all 

 the organic portion is driven ofF, while the inorganic "or mineral remains. 

 This organic part is called humus or vegetable mold, and is the result of the 

 action of the oxygen of the air upon dead vegetation in or upon the soil. Soils 

 containing less than 5 per cent of this vegetable mold are considered poor in 

 humus, those having 5 to 10 per cent are "humus soils," or those rich in 

 organic matter, while those with more than 10 per cent are peaty soils and are 

 found in very wet places. 



Kow let us look at growing plants for which agricultural soils must be 



