t water, passing through soils containing elements prejudicial to
vegetation, would carry them off, but would leave those which are
beneficial behind. We cannot make our water so discriminating; the general
merit of water of deep drainage is, that it contains very little. Its
perfection would be that it should contain nothing. We understand that
experiments are in progress which have ascertained that water, charged
with matters which are known to stimulate vegetation, when filtered
through four feet of retentive soil, comes out pure. But to return to our
wheat. In the first case, it shrinks before the cold of evaporation and
the cold of water of attraction, and it sickens because its feet are never
dry; it suffers the usual maladies of cold and wet. In the second case,
the excess of cold by evaporation is withdrawn; the cold water of
attraction is removed out of its way; the warm air from the surface,
rushing in to supply the place of the water which the drains remove, and
the warm summer rains, bearing down with them the temperature which they
have acquired from the upper soil, carry a genial heat to its lowest
roots. Health, vigorous growth, and early maturity are the natural
consequences. * * * * * * * * *

"The practice so derided and maligned referring to deep draining has
advanced with wonderful strides. We remember the days of 15 inches; then a
step to 20; a stride to 30; and the last (and probably final) jump to 50,
a few inches under or over. We have dabbled in them all, generally
belonging to the deep section of the day. We have used the words 'probably
final,' because the first advances were experimental, and, though they
were justified by the results obtained, no one attempted to explain the
principle on which benefit was derived from them. The principles on which
the now prevailing depth is founded, and which we believe to be true, go
far to show that we have attained all the advantages which can be derived
from the removal of water in ordinary agriculture. We do not mean that,
even in the most retentive soil, water would not get into drains which
were laid somewhat deeper; but to this there must be a not very distant
limit, because pure clay, lying below the depth at which wet and drought
applied at surface would expand and contract it, would certainly part with
its water very slowly. We find that, in coal mines and in deep quarries, a
stratum of clay of only a few inches thick interposed between two strata