darton.] NEW JERSEY. 41 
which is intermixed with considerable sand below and clay above. The 
basal beds are usually water-bearing. Fossil shells occur in greater or 
less abundance throughout the beds. The thickness of the formation 
averages about 45 feet, and is remarkably constant. 
REDBANK FORMATION. 
This is the "red sand" member, which lies between the Lower and 
the Middle Marl beds. In its unweathered condition it consists of an 
admixture of gray or dark sand with a moderate proportion of glauco- 
nite or greensand. Some clay admixture occurs locally, and the upper 
and lower beds are usually notably argillaceous. In its surface out- 
crop, which extends across the State along a narrow belt from Nave- 
sink Highlands to Salem, the glaucouite is weathered out and the 
residuary sands are stained red by the iron from this mineral. The 
thickness of the formation averages about 90 feet, and the local varia- 
tions are not large in amount. The sand is an important water bearer 
south of the latitude of Philadelphia, where it is mainly coarse sand of 
a medium -light color. 
RANCOCAS FORMATION. 
This, the Middle Marl bed, is considerably thinner than the Lower 
Marl bed, but it is a widespread and characteristic horizon. It is 
largely glauconitic, particularly in its lower portion. The upper beds 
contain much calcareous material, often to a sufficient degree to consti- 
tute an impure limestone. These beds are highly fossiliferous, and at 
their top carry the very distinctive layer of Terebratula harlani. 
MANASQUAN FORMATION. 
This is the lower portion of the Upper Marl bed. It consists of 
glauconitic marls, of which the richest beds are toward the top. The 
thickness has been estimated at G5 feet, but to the southward it 
increases somewhat. 
SHARK RIVER FORMATION. 
This is the upper portion of the Upper Marl bed, or the "blue marl" 
of local parlance. It is a highly glauconitic marl with some argilla- 
ceous admixture, and is recognized distinctly only in the area about 
Shark Eiver. Its thickness there is about 12 feet. 
CHESAPEAKE FORMATION. 
This great series of deposits overlies unconformably the Cretaceous 
greensand group. To the northwest it consists largely of very coarse 
materials, but these gradually become finer to the south and to the 
east, where the principal deposits are great beds of clays with inter- 
calated strata of water-bearing sands at various horizons. Several 
hundred feet of the clays are intermixed with diatom remains, which 
constitute a very definite horizon in the formation. The thickness of 
this diatomaceous clay bed has been revealed in the many deep wells 
