42 THE COASTAL PLAIN OF NORTH CAROLINA.

in some places transgress them onto older formations. They are uncon-
formable to the underlying Eocene. The Miocene deposits consist of
sands, clays, marls, and diatomaceous earth beds. Glauconitic mate-
rials are rarely found, and when found are probably derived from older
formations. The diatomaceous earth is most strikingly developed in
the basal Miocene formations of Virginia and Maryland, where it has
been known as “Richmond earth.” The calcareous marls are at times
cemented into limestone ledges. The fossils consist chiefly of littoral
and infralittoral forms in which the cetacea, mollusea, bryozoa, echino-
dermata, zoantharia, foraminifera, and diatomacea are chiefly repre-
sented.

The Miocene deposits of North Oarolina belong to the later facies of
Miocene sedimentation, the littoral phase being well developed in the
Yorktown formation to the north of the Hatteras axis and in the Duplin
formation to the south of the Hatteras axis, where the shell remains
are much broken by wave action. In the underlying St. Marys forma-
tion of the former area—the only other Miocene formation found in
North Carolina—the moderately fine argillaceous sands are of a dis-
tinctly infralittoral character. They rest unconformably on Eocene or
Cretaceous beds as the case may be. The fossils of the North Carolina
Miocene are varied and numerous.

Pliocene.

Pliocene or supposed Pliocene deposits of two very marked types
occur in the Coastal Plain region. The first is an infralittoral marine
deposit not known with certainty to oceur io the north of Cape Hat-
teras, although a detailed study of well borings ‘may show it to overlie
the Miocene beds toward the coast beneath the mantle of Pleistocene

deposits. To the southward this phase of the Pliocene is, however, well -_

developed and its characters are not unknown. The deposits of this
type, however, lie as far as known along the eastern margin of the
subaérial division of the Coastal Plain in somewhat detached basins.
It is called the Waccamaw formation in North Carolina, where it is
chiefly found in the region near the mouths of the Neuse and Cape =
Fear rivers. The isolated outerops are probably remnants of a once

continuous deposit. Whether the poorly developed Croatan deposits
should be ineluded cannot be determined with our present knowledge of

The second phase is a littoral and sublittoral phase, the exact age of
which in the absence of fossils has never been satisfactorily determined.
Tt is evidently of late Tertiary or early Quaternary time. It consists
of gravels, sands, and loams which were evidently laid down close to