additional foot on the top
of it, and not a three-foot ditch deepened an additional foot.

The lowest foot of a four-foot ditch is raised one foot higher, to get
it upon the surface, than if the ditch were but three feet deep. In
clays, and most other soils, the earth grows harder as we go deeper, and
this consideration, in practice, will be found important. Again: the
small amount of earth from a three-foot ditch, may lie conveniently on
one bank near its edge, while the additional mass from a deeper one must
be thrown further; and then is to be added the labor of replacing the
additional quantity in filling up.

On the whole, the point may be conceded, that the labor of opening and
finishing a four-foot drain is double that of a three-foot drain.

Without stopping here to estimate carefully the cost of excavation and
the cost of tiles, it may be remarked, that, upon almost any estimate,
the cost of labor, even in a three-foot drain in this country, yet far
exceeds the cost of tiles: but, if we call them equal, then, if the
additional foot of depth costs as much as the first three feet, we have
the cost of a four-foot tile-drain fifty per cent. more than that of a
three-foot drain. In other words, 200 rods of four-foot drain will cost
just as much as 300 rods of three-foot drain. This is, probably, as
nearly accurate as any general estimate that can be made at present. The
principles upon which the calculations depend, having been thus
suggested, it will not be difficult to vary them so as to apply them to
the varying prices of labor and tiles, and to the use of the plow or
other implements propelled by animals or steam, when applied to drainage
in our country.

The earliest experiments in thorough-drainage, in England, were at very
small depths, two feet being, for a time, considered very deep, and
large tracts were underlaid with tiles at a depth of eighteen, and even
twelve inches. It is said, that 10,000 miles of drains, two feet deep
and less, were laid in Scotland before it was found that this depth was
not sufficient. Of course, the land thus treated was relieved of much
water, and experimenters were often much gratified with their success;
but it may be safely said now, that there is no advocate known to the
public, in England, for a system of drainage of less than three feet
depth, and no one advocates a system of drainage of less than four feet
deep, except upon some peculiar clays.

The general principl