Bulletin 23. Potash in the Greensands of NJ, 1923 - State of New ...

GLAUCONIT_-BEARING AND ASSOCIATED FORMATIO_'S. 11
ern part of the Coastal Plain, where it is a valuable water-bearing
formation, but thins out southwestward and disappears in the vicinity
of Skyesville, in the northern part of Burlington County. It is the
"Red sand" of Cook and earlier wxiters but does not iuelude certain
sands in the southern part of the State that were erroneously correlated
by Cook with the "Red sand" of Monmouth County. With
the Tinton sand member at the top it is the uppermost formation of
the Monmouth group. The Tinton member consists of a bed of green
indurated clayey and sandy g]auconitic mar] 10 to 20 feet thick in
Monmouth County. Its fauna is more closely allied to that of the
Navesink than to that of the Redbank and is characterized by la_;c
numbers of crustacean claws. It is Cook's "indurated green earth,"
regarded by him as part of the "Red sand."
Hornerstown marL--The Hornerstown marl is a bed of glauconite
with clay and sand, having a total thickness of 30 feet or less. It
does not differ much in appearance from the Navesink, although
where unweathered it may have a greener tinge. Its fauna, though
meager, is different iu essential characteristics from the fauna of all
the underlying formations. A shell bed 4 to 7 feet thick at the top
of the formation is a conspicuous feature at many localities. The
bractfiopod Terebratula ttarlani, which occurs in great numbers in
the upper part of the shell bed, is perhaps the most distinctive fossil.
At the north the formation rests with apparent conformity on the
Tinton. Where that is absent it lies on the Redbank, and farther
south, owing to the disappearance of the Redbank, it is continuous
with the Navesink and not generally distinguished from it. It is
conformably overlain by the Vincentown sand except where overlapped
by Tertiary formations. It is the "Middle marl" of Cook
and the "Sewell marl" of Clark and forms the lower formation of
the Raneocas group, the Vincentown saml being the upper formation.
In Maryland the Rancocas deposits are not divided and are called the
Rancocas formation. The Hornerstown marl has been extensively
dug and used as a fertilizer.
Vincentown sand. The Vincentown sand presents two phases-
(l) a calcareous or lime sand, more or less indurated and largely a
mass of broken bryozoau, echinoid, coral, and other calcareous remains;
(2) a glauconitie quartz sand. The two occur in alternating
laycl_, although the lime sand is more common in the basal portion,
particularly to the south, and the quartz sand predominates in Monmouth
County. The fauna of the siliceous phase contains elements
of the Itornerstown fauna in association with forms characteristic
of the cMcareous phase. The thickness of the formation ranges
from 25 to 70 feet, but numerous well borings have shown that it
thickens down the dip--that is, toward the southeast--as do most
of the other formations. It rests conformably upon the Horners-
NEW JERSEY GEOLOGICAL SURVEY