84 THE COASTAL PLAIN OF NORTH CAROLINA.

Marlboro County and from thence, by way of Camden, Columbia, and
Hamburg, into Georgia in the vicinity of Augusta. (See geologic map,
Plate XVII, in pocket.)

The formation where present forms the basal division of the deposits of
the Coastal Plain and rests directly upon the eroded surface of the base-
ment rocks. The latter consist for the most part of early Paleozoic or
Proterozoic igneous and metamorphic rocks, but also to a limited
extent of sedimentary deposits of Triassic age (Newark). The upper
surface of the basement rocks where they are overlain by the deposits of
the Coastal Plain is very uneven. This is true not only with respect to
minor details, but likewise as regards certain larger features. This
unevenness is indicated, first, by the eastward extension at the surface
of long tongues of the older rocks; second, by the outcrop of isolated
patches of these rocks at considerable distances to the east of the Pied-
mont border; and, finally, by the depths at which they have been en-
countered in wells at various places. :

The formation is overlain unconformably by the Black Creek (“Bla-
den”) formation, or, where that is absent, by overlapping strata of the
Eocene, Miocene, Pliocene, or Pleistocene periods. The beds of the
Black Oreek formation form the immediate superjacent covering along
the southeastern edge of the belt of Patuxent occurrences. The ob-
served width of overlaps of these beds above water level varies from a
few miles to a maximum of at least 12 miles, the greatest width being
in the valley of Cape Fear River in southeastern Cumberland County.
The undulating Patuxent-Black Creek contact has been observed at
various places on Cape Fear, Neuse, Contentnea, and Tar rivers.

The relations of the Patuxent formation to Tertiary and younger
beds will be discussed in the order of age, beginning with the
oldest. But one area of Eocene is known within the belt. This is in
Harnett County, about 3 miles northeast of Spout Springs, where a bed
of siliceous limestone, probably of very limited extent, is poorly ex-
sa near the top of a hill. Its vertical position is perhaps about 300
ve above sea-level. It is believed to rest upon the Patuxent forma-
ree and is probably overlain by a surface covering of the Lafayette

rmation. From the southwestern edge of Wilson County northeast-
boc to Roanoke River the Patuxent formation is perhaps continuously
“tet ae of ae age, except where the latter have
Along thé -yallea iia wa a by Pleistocene terracing processes
Pacem hee sag - iver to Roanoke River the observed
leek ok ein all low, nowhere exceeding 15 feet above water

streams. It is probable that from Wilson County north-