chap, n.] MANURING THE SOIL. 29 
materials, probably in nearly the same state 
as it was left by the deluge. The surface- 
soils, on the contrary, are of comparatively 
recent date; and they have been slowly 
formed by the gradual crumbling of the sub¬ 
soil, and its inter-mixture with decayed 
animal and vegetable matter, and with other 
soils which may have been accidentally 
washed down upon, or purposely brought 
to it. In fields, and uncultivated places, the 
surface-soil is almost as hard, and as coarse 
in its texture, as the sub-soil on which it 
rests; but in gardens which have been long 
in cultivation, the surface-soil becomes so 
thoroughly pulverized by frequent diggings, 
and so mixed with the manure and decayed 
vegetables which have been added to it 
from time to time, that it is changed into 
the soft, light, fine, powdery substance, called 
garden-mould. If the sub-soil be naturally 
porous or well drained, this mould, however 
rich it may be made by the addition of de¬ 
cayed vegetable matter or animal manure, 
will always continue friable; and as long as 
it does so, it will be fit for the growth of 
plants: but if no vent be allowed for the 
