OF SOUTH CAROLINA. 233 
theory of gypsum. Some suppose that it acts by virtue of the lime, which it parts with slowly and 
as the plants require it. While Liebig holds that it acts by fixing the amonia brought down by the 
rain, and retaining it in the soil. But scarcely any one theory explains all the facis—for instance, 
its specific action on certain plants, its greater proportionate effect on manured and limed land, and 
its entire inertness on some lands. Nevertheless, a substance that, by a single top-dressing, is capa- 
ble of doubling a crop of clover, will be continued to be used where its effects are known, and the 
price not too high. 
In some countries, granite, in the first stages of disintegration, is spread on the land with good 
effect; and decomposed trap rock is applied in a similar manner. In the upper part of the State, 
there are many places exceedingly favorable for experiments of this sort, where one could be 
exchanged for the other. It is proper to observe, however, that the felspar of the granite must not 
have lost its crystaline form, nor be entirely soft, otherwise there will not be a sufficient quantity of 
potash left to repay the expense of carting, and the mechanical effects of the other ingredients 
would scarcely justify the experiment. 
The debris of the trap rocks would be an excellent application to the light soils by which they 
are generally surrounded. When taken from any distance below the surface, the earthy matter 
should be used sparingly, and allowed to remain on the surface for some time, because of the 
protoxide of iron which it contains. 
Clay is very abundant allover the State; when burned it is a good application, having both a 
mechanical and chemical value. The burning seems to liberate the silicate of lime, and perhaps 
other salts that may be present in a state that renders them insoluble under ordinary circumstances. 
In Europe, kilns are constructed for burning the clay; but I saw practiced in Darlington, by Col. 
Williams, the most simple and the least expensive mode of effecting this object, that has come to 
my notice. Along side a bank of clay, of considerable extent, thrown from a ditch, logs of wood 
were placed end to end in a single line; over this the clay was turned, completely covering the wood. 
One end of the wood was now fired, which continued to burn slowly, and to heat sufficiently the 
mass of clay, in its progress from one end to the other. The clay thus burned, was spread on the 
land not far from the spot, and with very satisfactory results. 
CALCAREOUS SUBSTANCES. 
Nature has bestowed on the State all the forms of carbonate of lime that can be useful in agri- 
culture. Along the coast there are beds, almost inexhaustable, of recent oyster shells, which could 
be carried, at a small expense, to the landings, where wood is abundant, aud converted into lime. 
The following analyses will show that their value as a manure is not altogether dependent upon 
the lime. 
“ 
Composition of Oyster Shells.* 
Ain imal@imemprane. =e on 2 bs See eee aoa em ean wins 0.5 
marbongtesOn winGe see eee o— ao ~ on eee ae oe eee ee. 98.5 
Phosphate . of #lime’— = === --=—. Rapes SL a ee en ee ee 1.0 
*Kane. 
we 
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