
SOILS AND SUBSOILS 383 
yields a soil comparable to that derived from the decom- 
position of certain gneisses and miica-schists. The soils 
formed upon chlorite-schist are commonly thin, gritty clays, 
often somewhat dark in colour, but relatively infertile, although 
hardly so barren as the soils derived from serpentine, quartzite, 
or clay-slate. 
Soils from Derivative Rocks.—These rocks consist, for 
the most part, of arenaceous and argillaceous materials ; 
amongst them, however, are included many important cal- 
careous rocks. No doubt there are numerous other kinds of 
derivative rocks, but inasmuch as the outcrops of these 
occupy very limited areas, they may be here disregarded. 
Sandstones, shales, and limestones are by far the most widely- 
spread of derivative formations. 
Arenaceous Rocks.—TYhe large majority of these rocks 
are quartzose, and they tend therefore to yield light soils, 
which are often not sufficiently retentive. But they show 
ereat differences in this respect, many containing larger or 
smaller percentages of argillaceous matter, and giving rise 
to loamy soils of excellent quality. Some white sandstones 
consist almost exclusively of quartz-grains, and owe their 
induration to compression alone. The soil formed upon a 
rock of this kind, it need hardly be said, will be a barren 
sand, incapable of tillage. Many sandstones, however, owe 
their induration to some cementing material that binds the 
grains together. The cement may be calcium carbonate, 
iron-oxide, argillaceous matter, or other substance. When 
such rocks are weathered, therefore, the nature of the cement- 
ing material necessarily affects the character of the soil. 
Again, it may be noted that, although quartz is the dominant 
ingredient of most sandstones, yet many other constituents 
are sometimes present. Thus sandstones immediately derived 
from the breaking-up of an igneous rock may consist to no 
small extent of felspar, mica, and other minerals in a more 
or less altered condition. Few sandstones, indeed, do not 
contain scales of mica, which are not infrequently so abundant 
as to impart a fissile structure to the rock. However plentiful 
these minerals may be in a sandstone itself, they are not 
often conspicuous in the overlying subsoil, and are usually 
completely wanting in the vegetable soil. It is obvious, 
