Maryland Geological Survey 71 



glauconite. In some places iron crusts of irregular shape are found, but 

 the indurated materials more often occur in the form of layers one or 

 two inches in thickness. At other times tubular or rounded concretions 

 occur which are filled with gray sand in which grains of unweathered 

 glauconite are present. 



The beds are very homogeneous over wide areas and in this respect are 

 not unlike the deposits of the Matawan, although they are more arena- 

 ceous and glauconitic. The alternating clays so common in the Matawan 

 are absent, and clay deposits generally are unfrequent. Because of the 

 similarity of the materials the Monmouth is, when unfossiliferous, dis- 

 tinguished with difficulty from the overlying Eocene Aquia formation, 

 although the broader relations show that a marked interval separated 

 the two. 



Strike, Dip, and Thickness. — The Monmouth formation has the same 

 general strike as the underlying formations, maintaining a nearly north- 

 east-southwest direction from eastern Cecil County to central Prince 

 George's County. The dip of the beds is to the southeast at the rate of 

 20 to 25 feet in the mile. The maximum thickness of the formation on 

 the northern Eastern Shore is about 100 feet. Along the Sassafras River 

 it is reduced to about 65 feet, and in Anne Arundel County to about 

 50 feet. It generally declines from this area southward until in central 

 Prince George's County it is only 20 to 25 feet in thickness, beyond 

 which it gradually thins out, due to the overlap of later formations. 



Stratigraphic and Structural Relations. — The Monmouth forma- 

 tion overlies the Matawan formation unconformably, although no marked 

 irregularities of surface have been observed in the region. The Mon- 

 mouth formation gradually transgresses the Matawan formation to the 

 southward until it comes to rest on the Magothy formation. It is the 

 most conspicuous transgression observed in the Upper Cretaceous section. 



The Monmouth formation is overlain unconformably by Tertiary 

 deposits both of Eocene and Miocene age, since the southwardly-trans- 

 gressing Aquia formation is in turn overlapped by the Calvert formation 

 so that both are at times found in contact with the Monmouth strata. 



