332 W. B. CLARK — UPPER CRETACEOUS FORMATIONS OF NEW JERSEY. 



when the face of the escarpment juts far out to the westward, continues 

 to hold this width for the most part throughout southern New Jersey. 

 The belt of outcrop is, however, very irregular and along some of the 

 deeper valley lines crossing the escarpment does not exceed a mile in 

 width. In Delaware and upon the eastern shore of Maryland the belt 

 again broadens and in the valley of the Sassafras river reaches five miles 

 in width. Upon the western shore of Maryland it is much narrower and 

 gradually tapers down until it entirely disappears just beyond the border 

 of Prince Georges county, with the possible exception of a single occur- 

 rence near Fort Foote, on the Potomac river. 



Character of materials. — The deposits of the Monmouth formation are 

 variable, but sands largely predominate. As different types of materials 

 to a large extent characterize the subdivisions, a more accurate descrip- 

 tion will be given of them in that connection. In general the sands are 

 highly ferruginous and to a large extent glauconitic, becoming also at 

 times very argillaceous toward the south. The sand deposits are fre- 

 quently indurated either by iron or by carbonate of lime, the latter being 

 furnished by the fossil shells which at times crowd the beds. 



Strike, dip, thickness. — The strike and dip of the Monmouth formation 

 are essentially the same as in the case of the Matawan formation, but 

 can be somewhat more readily determined on account of the topographic 

 situation of the strata. 



The thickness of the deposits is less variable than in the case of the 

 Matawan formation, but gradually declines from about 150 feet in north- 

 ern New Jersey to 60 feet to the east of Philadelphia, beyond which 

 point it continues to increase, reaching somewhat over 60 feet in Glouces- 

 ter county and about 85 feet in Salem county. In Delaware it is about 

 60 feet, and on the eastern shore of Maryland it increases in the region 

 of the Sassafras river to 85 feet. Upon the western shore of the Chesa- 

 peake bay, in the valleys of the Magothy and Severn rivers in Anne 

 Arundel county, its thickness is again reduced to 50 feet, beyond which 

 it rapidly declines, until in the valley of the Patuxent it is only 10 feet, 

 and shortly thereafter entirely disappears. 



Stratigraphic relations. — The Monmouth formation lies conformably 

 upon the Matawan formation throughout the area observed. The division 

 line is generally sharply defined where the basal red sands come in con- 

 tact with the micaceous sands and the sandy marls of the Matawan. 



The relations between the Monmouth formation and the overlying 

 Rancocas formation are not so clear on account of the very great difference 

 in the upper members of the Monmouth formation itself in the different 

 portions of its area of outcrop, the Rancocas formation resting through- 

 out a portion of the region upon red sands, while elsewhere it lies upon 



