GEOLOGICAL SECTION OF NEW JERSEY 369 
Clark, and forms a part of Cook’s Clay-marl series. It was formerly 
called the Columbus sand and is the equivalent of a part of the Mat- 
awan formation. 
Marshalltown clay-marl—The Marshalltown ranges from a 
black sandy clay to an argillaceous greensand marl. Locally it is 
abundantly fossiliferous, its characteristic species being in part 
recurrent forms from the Merchantville, and in part a new element, 
which recurs again in a higher formation although absent or incon- 
spicuous in the immediately succeeding beds. Its thickness is 30 
to 35 feet. It is a portion of the “laminated” sands which formed 
the upper part of the Clay-marl series of Cook, although in the south- 
western portion of the state he referred these beds to the Navesink 
(Lower) marl. It was included in Clark’s Hazlett sands, a sub- 
division of his Matawan. 
The Wenonah and Mount Laurel sands—Above the Marshall- 
town clay-marl there is a considerable thickness of sand regarding 
which there has been some difference of opinion. ‘The terms Wenonah 
and Mount Laurel have both been applied to them in whole or in 
part. Lithologically they are not sharply differentiated from each 
other, although the lower part (Wenonah) is generally a fine mica- 
ceous sand and the upper part (Mount Laurel) is coarser and contains 
considerable greensand. Paleontologically, however, they are quite 
distinct. ‘The Wenonah fauna is largely recurrent from the Wood- 
bury, with comparatively few prominent species common either to 
the Marshalltown below or the Mount Laurel and Navesink above. 
The same elements are prominent again still higher in the Red Bank. 
The Mount Laurel fauna is identical with that of the Navesink above, 
and is closely allied to the Marshalltown, but contains a foreign ele- 
ment, chief among which is the cephalopod Belemnitella americana 
and the brachiopod Terebratella plicata, so that the indistinct litho- 
logical line between the Wenonah and Mount Laurel sands is of 
considerable paleontological singificance. ‘The combined thickness 
of these formations is 40 to 80 feet, the Mount Laurel being limited 
to a very thin bed at Atlantic Highlands (Cook’s sand-marl) but 
increasing much in thickness toward the southwest. "The Wenonah 
sand is the highest bed correlated with the Matawan of Maryland, 
while the Mount Laurel is the base of the Monmouth. 
Navesink marl—The Navesink marl consists of greensand marl, 
