l run according to the
slope of the surface, in which case, by the way, no drains but those
across, could catch any of it except what fell upon the drains. But the
whole theory of drainage is otherwise, and is based on the idea that we
change the course of the underground flow, by drawing out the water at
given points by our drains; or, in other words, that "the water seeks
the lowest level in all directions."

Upon the best view the writer has been able to take of the two systems
as to the direction of drains, there is but a very small advantage in
theory in favor of either over the other, in soil which is homogeneous.
But it must be borne in mind that homogeneous soil is rather the
exception in nature than the rule.

Without undertaking to advance or defend any peculiar geological views
of the structure of the earth, or of the depositions or formations that
compose its surface, it may be said, that very often the first four feet
of subsoil is composed of strata, or layers of earth of varying
porosity.

Beneath sand will be found a stratum of clay, or of compact or cemented
gravel, and frequently these strata are numerous and thin. Indeed, if
there be not some stratum below the soil, which impedes the passage of
water, it would pass downward, and the land would need no artificial
drainage. Quite often it will be found that the dip or inclination of
the various strata below the soil is different from that of the surface.

The surface may have a considerable slope, while the lower strata lie
nearly level, as if they had been cut through by artificial grading.

The following figure from the Cyclopedia of Agriculture, with the
explanation, fully illustrates this idea.

"In many subsoils there are thin partings, or layers, of porous
materials, interspersed between the strata, which, although not of
sufficient capacity to give rise to actual springs, yet exude
sufficient water to indicate their presence. These partings
occasionally crop out, and give rise to those damp spots, which are
to be seen diversifying the surface of fields, when the drying
breezes of Spring have begun to act upon them. In the following
cut, the light lines represent such partings.

"Now, it will be evident, in draining such land, that if the drains
be disposed in a direction transverse or oblique to the slope, it
will often happen that the drains, no matter how skillfully
planned, wi