196 PHYSIOGRAPHY, GEOLOGY AND MINERAL RESOURCES

very homogeneous through considerable thicknesses. In certain hori-
zons the shells of organisms are found commingled with the glau-
conitic materials in such numbers as largely to make up the beds, pro-
ducing what is known as a greensand marl, and these beds are at times
so indurated as to form limestone layers. AV hen the glauconite is
weathered the deposits lose their characteristic gray and green color
and generally become lighter gray with reddish or reddish brown
streaks or bands, or may become entirely of the latter color. In this
condition they are often cemented into a ferruginous sandstone. The
unweathered deposits are found mainly in Charles and Prince George's
counties, while the weathered beds appear chiefly to the northward in
Anne Arundel county and upon the eastern shore of the Chesapeake.

The fossils of the Pamunkey formation are numerous and char-
acteristic and admit of separation into two clearly defined faunal
zones, the lower of which has been described as the Aquia Creek
stage and the upper as the Woodstock stage.

The Aquia Creek stage, so called from its typical development along
the banks of Aquia creek, a tributary of the Potomac, contains a
highly characteristic fauna, which has caused the correlation of this
division with the lower Eocene of the southern Atlantic and Gulf
states. No satisfactory stratigraphic limits have as yet been assigned
to this division and the deposits seem to grade gradually upward into
the overlying division.

The Woodstock stage, so called from its typical development at
Woodstock, Va., on the southern bank of the Potomac, about 15 miles
below Aquia creek, is characterized by a fauna which has been shown
to be the same as that contained in the middle Eocene in the Gulf
states. As above stated, no satisfactory stratigraphic line has as yet
been detected separating this division from that which is found be-
neath it, so that it may be regarded for the present simply as a faunal
zone.

THE NEOCENE PERIOD.

The Neocene deposits of Maryland occupy a broad area in the east-
ern portion of the state and consist of strata which attain greater
thickness than those of any other period represented in the Coastal