Many soil sections 50 or more feet in depth are exposed in the
dry-farming territory of the United States, and it has often been
demonstrated that the subsoil to any depth is capable of producing,
without further weathering, excellent yields of crops. This
granular, permeable structure, characteristic of arid soils, is
perhaps the most important single quality resulting from rock
disintegration under arid conditions. As Hilgard remarks, it would
seem that the farmer in the arid region owns from three to four
farms, one above the other, as compared with the same acreage in the
eastern states.

This condition is of the greatest importance in developing the
principles upon which successful dry-farming rests. Further, it may
be said that while in the humid East the farmer must be extremely
careful not to turn up with his plow too much of the inert subsoil,
no such fear need possess the western farmer. On the contrary, he
should use his utmost endeavor to plow as deeply as possible in
order to prepare the very best reservoir for the falling waters and
a place for the development of plant roots.

_Gravel seams.--_It need be said, however, that in a number of
localities in the dry-farm territory the soils have been deposited
by the action of running water in such a way that the otherwise
uniform structure of the soil is broken by occasional layers of
loose gravel. While this is not a very serious obstacle to the
downward penetration of roots, it is very serious in dry-farming,
since any break in the continuity of the soil mass prevents the
upward movement of water stored in the lower soil depths. The
dry-farmer should investigate the soil which he intends to use to a
depth of at least 8 to 10 feet to make sure, first of all, that he