e:--

Transition Fire Clay.
Clay Slate.

Silica 60.03 54.77
Alumina 14.91 28.61
Peroxide of iron 8.94 4.92
Lime 2.08 0.58
Magnesia 4.22 1.14
Potash 3.87 1.00
Soda -- 0.24
Carbonic acid } 5.67 8.24
Water }
---- ----
99.72 99.50

The sandstones are derived from the siliceous particles of granite and
other rocks, and consist in many cases of nearly pure silica, in which
case their disintegration produces a barren sand, but they more
frequently contain an admixture of clay and micaceous scales, which
sometimes form a by no means inconsiderable portion of them. Such
sandstones yield soils of better quality, but they are always light and
poor. Where they occur interstratified with clays, still better soils
are produced, the mutual admixture of the disintegrated rocks affording
a substance of intermediate properties, in which the heaviness of the
clay is tempered by the lightness of the sandstone.

Limestone is one of the most widely distributed of the stratified rocks,
and in different localities occurs of very different composition.
Limestones are divided into two classes, common and magnesian; the
former a nearly pure carbonate of lime, the latter a mixture of that
substance with carbonate of magnesia. But while these are the principal
constituents, it is not uncommon to find small quantities of phosphate
and sulphate of lime, which, however trifling their proportions, are not
unimportant in an agricultural point of view. The following analyses
will serve to illustrate the general composition of these two sorts of
limestone as they occur in the early geological formations:--

COMMON. MAGNESIAN.
|-------------------------| |----------------------|
Mid-Lothian. Sutherland. Sutherland. Dumfries.

Silica 2.00 7.42 6.00 2.31
Peroxide of iron } 0.45 0.76 1.57 2.00
and alumina }
Carbonate of lime 93.61 84.11 50.21 58.81
Carbonate of } 1.62 7.45 41.22 36.41
magnesia }
Phosphate of lime 0.56 ... ... ...
Sulphate of