70 The Upper Cretaceous Deposits of Maryland 



The Monmouth Formation 



Name and Synonymy. — The Monmouth formation was so named by 

 the writer ' from Monmouth County, New Jersey, where the deposits of 

 this formation are characteristically developed. These deposits were 

 formerly known in Xew Jersey under the name of the Lower Marl Bed 

 and the Red Sand. Darton considered the Monmouth formation as the 

 upper part of his Severn formation. Uhler discussed these deposits 

 under lithologic names which cannot be readily recognized. The present 

 writer divided the New Jersey Monmouth formation into the Mt. Laurel 

 sands, the Navesink marls, and the Redbank sands and these have been 

 more recently employed as formational units by the New Jersey geologists. 

 These subdivisions cannot be recognized in Maryland. 



Areal Distribution. — The Monmouth formation extends from the 

 Delaware boundary to southern Prince George's County, a few miles to 

 the south of Washington. The width of outcrop is variable, reaching 4 or 

 5 miles in maximum extent in Cecil County, but rapidly narrowing in 

 Kent County, where it is reduced to about 2 miles in width. In Anne 

 Arundel and Prince George's counties it occupies a very irregular line of 

 outcrop due to the higher country, the strata being traced from the hill- 

 tops in the northwest down the valley lines to their disappearance at tide 

 level, and therefore often reaching a total width of outcrop in the 

 stream channels along the dip of 4 to 5 miles. Farther to the south- 

 westward in Prince George's County the Monmouth forms a narrow band 

 which finally disappears by the overlap of later formations. 



Lithologic Characters. — The Monmouth formation consists chiefly 

 of reddish and pinkish sands, generally glauconitic, the beds in places 

 forming a dark greensand. The glauconitic feature is much more marked 

 than in the preceding Matawan. When un weathered the glauconitic beds 

 are dark green or nearly black in color, but become reddish-brown when 

 weathering. 



The deposits are commonly loose and unconsolidated, but are locally 

 indurated by the ferruginous cement derived from the weathering of the 



1 Clark, Wm. Bullock, Bull. Geol. Soc. Amer., vol. viii, pp. 331-336, 1897. 



