OF SOUTH CAROLINA. 219 
Sands are known as bad conductors of heat, and hence the high temperature they attain. The 
temperature of the earths decrease in proportion to the absence of sand. 
Capacity to become heated, when exposed to the sun’s rays.—lIt is a fact, long since established, 
that substances acquire different degrees of temperature, when exposed, under the same circum- 
stances, to the sun’s rays. The terms warm and cold, applied to soil, have, generally, reference to 
color and moisture, and not without reason, for these affect, very materially, the degree of tempera- 
ture acquired by the soil. The state of the surface, the composition, and the manner in which the 
soil lies, as affecting the angle of incidence of the sun’s rays, are also modifying circumstances. 
The results of the experiments are as follows. 
Kinds of earth. THighest tenyperature. 
Soils moist. Soils dry. 
Silicious sand, yellowish gray- -.---- 37.25. <. <- 44.75 
Caleareous sand, whitish gray- -- -- -37.38_ ~~ -- -44.50 
Gypsum, whitish gray. ---------- -.386.25- ---- -43.62 
Poor clay, yellowish---...-----~--- 36.75_.- -. -44.12 
Roth Clays ee ee eer en= needa O00 
Argillaceous earth, yellowish gray- -.37.38- -- -- -44.62 
Calcareous earth, white- -- -- -- -.- --35.63_ -- -- -43.00 
Humus, blackish gray------- ---- -39.75- -- -- -47.37 
Garden earth, blackish gray- ------37.50- -- -- -45.25 
Besides the physical properties thus presented, there are other modifying circumstances that 
greatly affect the fertility of arable land. Among these are the depth and texture of the soil. It 
is not difficult to distinguish, in a newly ploughed furrow, the depth of the superficial layer, or soil 
proper: it varies from a few inches to twelve or thirteen, and, in extraordinary cases, such as 
swamps, river bottoms, and where the native forests have deposited the growth of ages on planes, 
almost level, such as the prairies of the West, it amounts to many feet. 
Depth of soil is always of great importance, for it allows the roots of plants to penetrate and draw 
nutriment from below ; besides, by working deeper, we may ameliorate the surface. Deep soils 
suffer less from excess or deficiency of moisture. The rain, when it falls, is absorbed by the soil, 
and retained, as in a reservoir. 
Climate also exerts a marked influence on soils, as well as on plants. A thin, sandy soil, that is 
productive in a moist climate, may be almost barren in a drier one; hence the necessity of a know- 
ledge of the meteorological character of a country, in order to arrive at a correct knowledge of the 
value of its arable land. I apprehend that serious mistakes are often the result of ignorance on 
this subject, when comparing the practice of agriculturists, where there is much difference of cli- 
mate. In general terms, a stiff soil is better adapted to a dry climate, and a light soil, to one that is 
moist. 
In some countries deficiencies of moisture are compensated by skilful irrigation—a practice thatis 
totally neglected with us, excepting on the rice plantations, where it is pursued most successfully. 
Before proceeding to the consideration of those means of improving soils indicated by geology, 
it will be proper to examine more closely the conditions of fertility, dependent on chemical compo- 
sition. 
The question is often asked, what are the constituents of a really fertile soil, and in what 
