OF SOUTH CAROLINA. 213 
slates, in that part of Edgefield and Lexington lying along the Saluda, and the trap soils of Cam- 
bridge. The mica slate soils of Abbeville are as readily distinguished from those of the gneiss of 
Anderson and Greenville; while the soils derived from the talcose slates of Lancaster, cannot be 
mistaken for either. 
This is equally true in relation to the origin of the soils of the Tertiary region, although not 
quite so obvious; for the deposits of which it is composed are made up of finely comminuted mat- 
ter, already in a state to enter into the composition of the soil, being, as we have seen, the ruins 
of the older rocks. They are also more uniform in composition, and changes, dependent upon geo- 
logical structure, are, therefore, less frequent. Nevertheless the character of the soils may be traced 
invariably to the subjacent deposits. 
In the conversion of rocks into soil, two agencies are principally concerned: the mechanical 
action of water, influenced by changes of temperature, and the chemical effects of carbonic acid, 
held in solution by rain and spring water. Those rocks that imbibe this fluid freely, or that are so 
fissured as to allow of its percolation, are broken into fragments or reduced to dust, by the expan- 
sion consequent on freezing. In the crystalline rocks the feldspar, hornblende, mica, and protoxide 
of iron, of which they are composed, are subject to decomposition by every shower of rain that 
brings down carbonic acid from the atmosphere. 
The nature and progress of disintegration and decomposition have been already explained. It is 
only necessary, in this place, to state that the surface of the rocks is reduced to a crumbling mass, 
of variable depth, which, by the continued action of atmospheric agencies, passes into a yellowish 
clayey stratum, known as the sub-soil; anda portion of this, by the oxidation of the iron and 
addition of organic matter, assumes a darker color, becomes less adhesive, and constitutes the ara- 
ble soil, fitted for the growth of plants. Did the soil lose no part of the constituents of the rock 
from which it is derived, it is obvious that it would be nearly identical with it, in chemical compo- 
sition; but as the silicious portion alone is insoluble, the rest must be subject to be dissolved, and 
washed away by the rains—and hence the meteorological, as well as the topographical, character of 
a country, exerts a powerful influence on the fertility of its soil. The depth to which the rocks are 
subject to disintegration has also an important bearing in this relation. Granite is frequently very 
indestructible, and when so, the soil derived from it is thin, and often barren. But along the Atlan- 
tic slope, from Maryland to Alabama, this rock undergoes disintegration to a depth for which it is 
difficult to account. he granitic soils are, therefore, far from barren, and, in South Carolina, are 
valued, as cotton lands. 
It will be recollected that granite proper, is composed of quartz, felspar and mica, and that the 
felspar contains potash or soda, with which the carbonic acid of the atmosphere, brought down by 
the rains, combines, forming a highly soluble salt, carbonate of potash or soda, which, to a greater 
or less extent, dependent on the circumstances, is washed away. When the disintegration takes 
place upon a steep hill side, and proceeds but to a slight depth, the whole of the potash is removed, 
leaving little more of the felspar than a silicate of alumina or porcelain clay. The mica is subject, 
though in a less degree, to a similar process, and it is evident that such a soil must be almost, if not 
entirely, barren. 
I have observed that when a hill is capped with granite undergoing disintegration, that the soil on 
the sides is much more fertile, and I saw on Stone House Creek, Chesterfield District, an, excellent 
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