DISTRIBUTION AND CHARACTER OP RANCOCAS FORMATION. 337 



and four miles, but this width is considerably increased by the ex- 

 posures which are made by the easterly flowing streams, but more espe- 

 cially by the outliers which are found upon the higher points of the 

 escarpment. Its areal distribution decreases in width in central Mon- 

 mouth county to some extent on account of the topographic configuration 

 of the country, but in central and southern New Jersey, on account of the 

 greater thickness of the deposits, considerably expands, until in Camden 

 and Gloucester counties it reaches a width of five or six miles. Toward 

 the south, in Salem county, it again somewhat contracts. In Delaware 

 and the eastern counties of Maryland, on account of the extremely level 

 character of the country, its area of outcrop is increased, but it narrows 

 southward toward the shore of Chesapeake bay, and is only represented 

 in a few isolated remnants on the western side, and entirely disappears 

 on the north bank of Severn river. 



Character of materials. — The deposits of the Rancocas formation consist 

 for the most part of greensand marls, at times very highly calcareous, 

 especially in central and southern New Jersey. Some of the beds are 

 crowded with fossils, so that shelly bands occur which are often locally 

 indurated. The greensand marls frequently become highly argillaceous, 

 producing a chocolate colored marl. 



Strike, dip, thickness. — The strike and dip of the deposits of the Rancocas 

 formation conform more or less closely to those of the preceding members 

 of the upper Cretaceous, and can be quite readily determined on account 

 of the topographic relations of the strata. The dip, obtained by connect- 

 ing the beds upon the crest of the escarpment with the main body of the 

 deposits to the eastward, is shown to be on the average about 25 feet in 

 the mile. 



The thickness of the deposits is fairly constant throughout the northern 

 portion of the area to the north of Rancocas creek, and has been esti- 

 mated to be between 45 and 50 feet. To the south of this region it 

 slightly increases in thickness through Camden and Gloucester counties, 

 and then suddenly expands in Salem county, where it attains a maxi- 

 mum thickness of 125 feet. To the south of the Delaware river, on the 

 Delaware peninsula, it declines rapidly in thickness, and at the Maryland 

 state line has again become reduced to about 50 feet. Near the shore of 

 Chesapeake bay it has still further declined to 30 feet, while upon the 

 western shore of the bay, in eastern Anne Arundel county, the deposits 

 are onty a few feet in thickness at the isolated points observed. 



Stratigraphic relations. — The relations between the Rancocas formation 

 and the underlying Monmouth formation have already been described. 

 The materials of the Rancocas formation are very distinct from the beds 

 beneath and give indication, both upon this and other grounds, as has 



