1 64 The American Geologist. September, 1905 
The Monmouth Formation. 
'Phis includes the Redbank, the Navesink, and the Mt. 
Laurel sand, and was so named by Clark from its typical 
exposure in Monmouth county. 
The Redbank Formation^ 
The Redbank formation which is about ioo feet thick at 
Atlantic Highlands is overlaid by the Long Branch beds or 
in its absence by the Columbian gravels, and rests on the 
Navesink beds below. It is generally of a bright red color 
probably due, as Clark states, to the oxidization of the 
glauconite grains contained in it. The color is not always 
a deep red and often varies from almost colorless to a ver- 
milion. The colors, yellow, slate, salmon, pink and red 
are well represented in the samples I have taken. It is a 
sand and shows by its thickness, distribution and character 
of its material that it marks an important change in the 
history of the Cretacic beds of the Atlantic coastal plain. 
At the top of the Redbank is an indurated bed called 
by Weller the "Tinton bed." It is probably represented at 
'Atlantic Highlands by the indurated bed which occurs just 
beyond Hilton station, and between this point and Water- 
witch (see plate). This bed is about 18 feet thick and 
higher up contains pockets of greensand which still retain 
the green color, although the surrounding material is red. 
Mica flakes are very abundant in the Redbank, and are 
very characteristic. When the material is colored a deep 
red there seems to be an absence of glauconite grains, but 
grains of magnetite are found which might have resulted 
from an alteration of the glauconite. Some pieces of limo- 
nite about the size of one's hand were collected from the 
Redbank, which must be considered as due to the concentra- 
tion of the iron derived from the glauconite. Samples 
examined under the microscope show the Redbank sand to 
be composed largely of quartz grains of uniform size often 
cementetd by fine clay colored by iron. M'ica, magnetite, 
orthoclase, microcline, and mornblende are common. 
Concretions of limestone are common, both rounded 
and stalactitic in form. 
The Redbank forms a large part of the hills around 
Atlantic Highlands. Its thickness and color make it an im- 
