gh the soil renders it
more porous, so that it is easier for the water falling afterward to pass
down to the drains, but no very satisfactory reason for this has been
presented, beyond that which is connected with the cracking of the soil.
The fact is well stated in the following extract from a letter to the
_Country Gentleman_:

"A simple experiment will convince any farmer that the best means of
permanently deepening and mellowing the soil is by thorough drainage, to
afford a ready exit for all surplus moisture. Let him take in spring,
while wet, a quantity of his hardest soil,--such as it is almost impossible
to plow in summer,--such as presents a baked and brick-like character under
the influence of drought,--and place it in a box or barrel, open at the
bottom, and frequently during the season let him saturate it with water.
He will find it gradually becoming more and more porous and
friable,--holding water less and less perfectly as the experiment proceeds,
and in the end it will attain a state best suited to the growth of plants
from its deep and mellow character."

It is equally a fact that the ascent of water in the soil, together with
its evaporation at the surface, has the effect of making the soil
impervious to rains, and of covering the land with a crust of hard, dry
earth, which forms a barrier to the free entrance of air. So far as the
formation of crust is concerned, it is doubtless due to the fact that the
water in the soil holds in solution certain mineral matters, which it
deposits at the point of evaporation, the collection of these finely
divided matters serving to completely fill the spaces between the
particles of soil at the surface,--pasting them together, as it were. How
far below the surface this direct action extends, cannot be definitely
determined; but the process being carried on for successive years,
accumulating a quantity of these fine particles, each season, they are, by
cultivation, and by the action of heavy showers falling at a time when the
soil is more or less dry, distributed through a certain depth, and
ordinarily, in all probability, are most largely deposited at the top of
the subsoil. It is found in practice that the first foot in depth of
retentive soils is more retentive than that which lies below. If this
opinion as to the cause of this greater imperviousness is correct, it will
be readily seen how water, descending to the drains, by carrying these
soluble and finer parts