uires draining, is that which, at some time during the year,
(either from an accumulation of the rains which fall upon it, from the
lateral flow, or soakage, from adjoining land, from springs which open
within it, or from a combination of two or all of these sources,) becomes
filled with water, that does not readily find a natural outlet, but
remains until removed by evaporation. Every considerable addition to its
water wells up, and soaks its very surface; and that which is added after
it is already brim full, must flow off over the surface, or lie in puddles
upon it. Evaporation is a slow process, and it becomes more and more slow
as the level of the water recedes from the surface, and is sheltered, by
the overlying earth, from the action of sun and wind. Therefore, at least
during the periods of spring and fall preparation of the land, during the
early growth of plants, and often even in midsummer, the
_water-table_,--the top of the water of saturation,--is within a few inches
of the surface, preventing the natural descent of roots, and, by reason of
the small space to receive fresh rains, causing an interruption of work
for some days after each storm.

If such land is properly furnished with tile-drains, (having a clear and
sufficient outfall, offering sufficient means of entrance to the water
which reaches them, and carrying it, by a uniform or increasing descent,
to the outlet,) its water will be removed to nearly, or quite, the level
of the floor of the drains, and its water-table will be at the distance of
some feet from the surface, leaving the spaces between the particles of
all of the soil above it filled with air instead of water. The water below
the drains stands at a level, like any other water that is dammed up. Rain
water falling on the soil will descend by its own weight to this level,
and the water will rise into the drains, as it would flow over a dam,
until the proper level is again attained. Spring water entering from
below, and water oozing from the adjoining land, will be removed in like
manner, and the usual condition of the soil, above the water-table, will
be that represented in Fig. 3, the condition which is best adapted to the
growth of useful plants.

In the heaviest storms, some water will flow over the surface of even the
dryest beach-sand; but, in a well drained soil the water of ordinary rains
will be at once absorbed, will slowly descend toward the water-table, and
will be removed by th