WATER RESOURCES. 349

GEOLOGIC OCCURRENCE AND CHARACTER OF THE UNDERGROUND
WATERS.

BASEMENT ROCKS.

The rocks which form the basement on which the deposits of the
Coastal Plain rest consist in the main of ancient crystallines and
metamorphics of early Paleozoic or Proterozoic age. They are the
eastward continuation of rocks of similar kind which form the greater
part of the surface throughout the Piedmont Plateau province. Along
the northwestern edge of the Coastal Plain the upper surface of these
rocks is. very uneven, but in general it dips to the southeast and passes
gradually deeper and deeper until along the immediate coast it lies at
depths of 1,200 to perhaps 2,500 feet beneath the present surface. It
is only along the northwestern border of the Coastal Plain province in
a belt some 25 or 30 miles in width, where their buried surface lies at
less than 300 or 350 feet below the present surface, that these basement
rocks form an important source of water supply. (See map, Plate
XXXI.) The artesian conditions which they present, except as slightly
modified by the overlying sedimentary beds, are identical with those
presented by the rocks of the Piedmont province proper farther to the
west. Their treatment here may perhaps be regarded as inappropriate,
but since they lie within the area under consideration, a brief state-
ment of their importance as water bearers may not be out of order.

In the belt indicated a large number of wells have been drilled
through the overlying deposits of the Coastal Plain into these base-
ment rocks. Many of them furnish ‘an abundance of good water suffi-
cient for use as municipal supplies and for steaming purposes in
boilers. Others yield smaller amounts sufficient for the domestic use
of one or more families; while some have been failures. From the
nature of the rocks it is in most places impossible to predict the out-
come of attempts to obtain water from this source. In the case of
erystalline rocks “which show neither bedding planes nor schistosity
the underground circulation depends upon the presence of fissures and
the connection of these channels either with the surface or with other
water-bearing formations, and obviously the striking of such fissures
is more or less a matter of chance. In the case of metamorphosed sedi-

_ ments in which the bedding planes have not been obliterated, or in
the case of rocks possessing well-developed schistosity, a regular sys-
tem of water horizons may exist. If the structure of these rocks can

ee be made out it becomes possible to predict with some confidence where

   

such horizons will be encountered. But in a region such as the one