follows, and calls his method
the combined system of deep and shallow drainage:

"In order to secure the full effect of thorough drainage in clays,
it is necessary that there should be not only well-laid conduits
for the water which reaches them, but also subsidiary passages
opened through the substance of the close subsoil, by means of
atmospheric heat, and the contraction which ensues from it. The
cracks and fissures which result from this action, are reckoned
upon as a certain and essential part of the process.

"To give efficiency, therefore, to a system of deep drains beneath
a stiff clay, these natural channels are required. To produce them,
there must be a continued action of heat and evaporation. If we
draw off effectually and constantly the bottom water from beneath
the clay and from its substance, as far as it admits of
percolation, and by some other means provide a vent for the upper
water, which needs no more than this facility to run freely, there
seems good reason to suppose that the object may be completely
attained, and that we shall remove the moisture from both portions
as effectually as its quantity and the substance will permit.
Acting upon this view, then, after due consideration, I determined
to combine with the fundamental four-feet drains a system of
auxiliary ones of much less depth, which should do their work
above, and contribute their share to the wholesome discharge, while
the under-current from their more subterranean neighbors should be
steadily performing their more difficult duty.

"I accomplished this, by placing my four-feet drains at a distance
of from eighteen to twenty yards apart, and then leading others
into them, sunk only to about two feet beneath the surface (which
appeared, upon consideration, to be sufficiently below any
conceivable depth of cultivation), and laying these at a distance
from each other of eight yards. These latter are laid at an acute
angle with the main-drains, and at their mouths are either
gradually sloped downwards to the lower level, or have a few loose
stones placed in the same intervals between the two, sufficient to
ensure the perpendicular descent of the upper stream through that
space, which can never exceed, or, indeed, strictly equal, the
additional two feet."

There are