soils). The earth is used by the human
race in many other ways. Human habitations and constructions rest on it
and penetrate it. It is the basis for transportation, both by land and
water. Its water powers are used. In these various relations the
applications of geology are too numerous to classify, much less to
describe. While only a few of these activities have in the past required
the participation of geologists, the growing size of the operations and
increasing efficiency in their planning and execution are multiplying
the calls for geologic advice. The nature of such applications of
geology may be briefly indicated.[64]

FOUNDATIONS

The foundations of modern structures such as heavy buildings, especially
in untried localities, require much more careful consideration of the
substrata than was necessary for lighter structures. In planning such
foundations, it is necessary to know the kinds of rocks to be excavated,
their supporting strength, their structures, the difficulties which are
likely to be caused by water, and other geologic features. Failure to
give proper attention to these factors has led to some disastrous
results.

The planning of foundations and abutments of bridges requires similar
geologic knowledge. In addition, there must be considered certain
physiographic factors affecting the nature and variation of stream flow
and the migration of shore lines.

SURFACE WATERS

Construction of great modern dams is preceded by a careful analysis of
sub-surface conditions, in regard to both the rocks and the water. It is
necessary to know the supporting strength of the rocks in relation to
the weight of the dam; to know whether the rocks will allow leakage
around or beneath the dam; and to know whether there are any zones of
weakness in the rocks which will allow shearing of foundations under the
weight of the dam in combination with the pressure of the ponded water.
It is necessary to know whether the valley is a rock valley or whether
it is partially filled with rock debris; if the latter, how deep this
debris is, and its behavior under load and in a saturated condition.
Here again physiographic factors are of vital importance, both in
relation to the history of development of the valley, and to questions
of stream flow and reservoir storage.[65]

Construction of dams is only an item in the long list of engineering
activities related to surface waters. River and harbor improvements of a
vast range l