GEOGRAPHICAL VARIATION IN THE MATERIALS. 345 



bed to the most important member of the formation. Although the 

 triple division again appears in Delaware and upon the eastern shore of 

 Maryland, it is lost upon the western side of the Chesapeake, where the 

 upper and lower sands with their intervening greensand marls, so well 

 developed in the two areas above described, become merged into pinkish 

 and grayish sands which show no persistent divisions, although possessing 

 more or less variability in their different parts. The highly glauconitic 

 character of the deposits in Monmouth county is gradually lost toward 

 the south, the greensand strata becoming at first more or less argillaceous, 

 while, to the south of the Delaware, both upon the eastern and western 

 sides of the Chesapeake, sands with little glauconite largely predominate, 

 and to the west of the Chesapeake alone represent the formation. 



The Rancocas formation is much more highly glauconitic in New 

 Jerse} r than it is south of the Delaware. The lower greensand member 

 gradually decreases south of Monmouth county, while the upper calcare- 

 ous member increases in thickness, until in the southern portion of New 

 Jersey it far surpasses the lower greensand division in importance. The 

 great thickness of the calcareous beds in Salem county, New Jersey, is 

 one of the most striking things connected with the geographical variation 

 in the materials of the Upper Cretaceous formations. Although the cal- 

 careous member is found to the south of the Delaware, it rapidly declines 

 in thickness upon the Delaware peninsula, beyond which it is not known 

 with certainty to occur, the few feet of Rancocas materials found on the 

 western shore being for the most part greatly weathered, so that their 

 original lithologic characters are much obscured. 



The Manasquan and Shark River formations show unimportant geo- 

 graphical variations in their materials. Their area of distribution along 

 the strike, as represented by surface outcrops, is far less in extent than 

 is the case with the other members of the Upper Cretaceous series, and 

 even in their area of occurrence they are largely obscured by the over- 

 lying Miocene. 



The variations thus far described have had to do entirely with geo- 

 graphical variations along the line of strike as shown either in surface ex- 

 posures or in well-borings near the margin of the several deposits. Some 

 of the deeper well-borings which have been made to the southeast of 

 the Cretaceous belt, down the dip of the beds, show that in general the 

 various members of the Upper Cretaceous series increase in that direction 

 both in thickness and in the amount of glauconitic materials which they 

 contain. The records of the well-borings, on account of the mixture of 

 materials which is liable to result from the methods pursued, do not al- 

 ways afford an accurate account of the beds penetrated ; but, so far as 

 can be judged, the broader formational distinctions which prevail at the 



