MARYLAND GEOLOGICAL SURVEY 195

The Rancocas formation consists of greensand marls, which in some
localities are highly calcareous on account of the large number of
shells of various molluscan forms. In general the deposits are quite
arenaceous and are commonly less glauconitic than the same beds
in New Jersey. The deposits have a thickness of from 50 to 60 feet
in Kent county, where they are most extensively developed, but on
the western shore of the Chesapeake they nowhere appear at the sur-
face with a greater thickness than 4 or 5 feet.

The fossils of the Rancocas formation are highly characteristic and
are in the main quite distinct from those which are found in the
Matawan and Monmouth formations. Their upper Cretaceous age is,
however, clearly apparent, and they are generally regarded as occupy-
ing a very high position in that division.

THE EOCENE PERIOD.

The deposits overlying the Cretaceous formations, above described,
have, from a very early period, been regarded as of early Tertiary
age, although our knowledge of them was confined to a few localities
from which characteristic fossils had been obtained. Later study,
however, has shown both the proper stratigraphic and paleontologic
relations of these deposits, so that they are now well understood.

THE PAMUNKEY FORMATION. —The Pamunkey formation, so called
from its highly characteristic development in the valley of the
Pamunkey river in Virginia, extends across Maryland from northeast
to southwest, through the counties of Kent and Queen Anne's on the
Eastern Shore and of Anne Arundel, Prince George's and Charles in
southern Maryland.. Its area of outcrop constantly broadens from the
Delaware line (to the north of which it is buried by the transgression
of the Neocene deposits) toward the southwest, and in the valley of the
Potomac river has a width of more than 15 miles.

The deposits of the Pamunkey formation are highly glauconitic and
are found in their unweathered state either as dark gray or green
sands or clays. The glauconite varies in amount from very nearly
pure beds of that substance to deposits in which the arenaceous and
argillaceous elements predominate, although the strata are generally