394 



THE SOUTHERN PLANTER. 



[July 



River, except as local drift. It differs, of 

 course, from the rocks beneath; and fre- 

 quently gives a fertile soil, immediately over 

 rocks which would have produced only a 

 barren desert. 



(10). Beneath the stratilBed rocks, in 

 many places rising up through and often 

 over-lying them, we find the im stratified 

 rocks. These bear no marks of having 

 been deposited by water, but seem to be of 

 volcanic origin. 



The most prominent minerals which enter 

 into the composition of these rocks are Feld- 

 spar, Hornblende, Epidote, Quartz, and 

 Mica. These combining, give us Trap 

 rocks, Granite (including Syenite), and 

 many less abundant varieties, of which we 

 have not room to give a description. 



Origin of Soils. — Whenever the rocks, 

 whether stratified or unstratified, are long ex- 

 posed to the influence of air, rain, and frost, 

 or even of air and rain alone, they are 

 gradually broken down, as heretofore stated, 

 into small fragments. These undergo many 

 subdivisions, until the little separated par- 

 ticles of sand and clay, mingled with such 

 organic matter as previously existed in the 

 rock, or has meanwhile been growing among 

 the fragments of its half-formed soil, become 

 one mixed mass, and at the same time pass 

 through such chemical changes as adapt 

 them to the great end for which they were 

 designed. 



The original quality of the soil must, 

 then, be greatly dependent upon the char- 

 acter of the rocks out of which it has been 

 formed. It is not difference in the mineral 

 composition of rocks alone, that causes 

 differences in the nature of soils; the organic, 

 fossil matter, deposited when the rocks were 

 formed, seems often to have had a most 

 striking influence. Any one may observe 

 for himself, in traversing a hilly or moun- 

 tainous region, how suddenly he sometimes 

 passes from one quality of soil to another, 

 even in the same field. And in unculti- 

 vated lands, he may frequently meet not 

 only with abrupt changes in the rocks and 

 soil, but changes just as abrupt in the trees, 

 shrubs, and iveech, which nature seems to 

 have adapted to the varying quality of their 

 mineral food. 



Pure granitic soils contain the disinteg- 

 rated particles of quartz, feldspar, and mica, 

 from the granite rock. The feldspar is soon 

 decomposed, by the action of carbonic acid, 

 into carbonate of potash and fine clay. The 



little crystals of quartz are but slightly 

 modified, forming, when set free, sand of 

 various degrees of fineness. From hilly 

 lands the fine clay is gradually carried down 

 into the low grounds, and a covering of 

 sand, generally with clay beneath it, is left 

 to form the poor, barren soils of the sur- 

 rounding hills. But even where all the 

 m.aterial of the granite is retained, the soil 

 is generally deficient in lime, magnesia, and 

 oxide of iron. 



When granite contains hornblende,'^ as it 

 often does, this furnishes lime, magnesia, 

 and iron, and such a soil is generally pro- 

 ductive. Or, if granite and trap rocks occur 

 on the same hill, the soils from both may 

 become mingled by the action of rain and 

 frost, or by tillage, and thus form a better 

 soil than either would form alone. 



Trap rocks, being composed, as we have 

 learned, of feldspar and hornblende, are 

 acted upon by air and water, both mechani- 

 cally and chemically. The result is a finely 

 divided soil, to which the feldspar fur- 

 nishes an abundance of clay and potassa, 

 with some soda ; while the hornblende 

 yields lime, magnesia, and oxide of iron 

 abundantly ; hence such soils are generally 

 fertile. Some of the best soils of Eastern 

 Virginia are formed from Trap. 



The primary stratified rocks differ widely 

 in composition, and, as a consequence, give 

 a great variety of soil. We have a most 

 extensive illustration of this in the greater 

 part of the wide area, extending from the 

 eastern side of the Blue Ridge, on the one 

 hand, to the slope over which the rivers 

 flowing into the Atlantic fall, before they 

 reach tidewater, on the other; then, ex- 

 tending northward, it becomes narrower as 

 it passes into Maryland, and extending 

 Southward into North and South Carolina, 

 it spreads out to a still greater width than 

 it has in Virginia. In this region there are 

 some belts of fine soil, formed from rocks 

 composed largely of feldspar and horn- 

 blende. There are other sections, in which 

 the soils are composed of the ruins of 

 gneiss and granite. These soils are sandy, 

 and less valuable. Again, there are local- 

 ities in which the soil has originated from 

 rocks composed chiefly of quartz, with small 

 quantities of mica or feldspar, or both. 

 Such regions are hopelessly deficient in 



* Granite, containing a considerable amount 

 of liornblende, is called " syenite." 



