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



well-borings, are frequently grayish or light greenish gray in color. They 

 have a thickness of about five feet in the vicinity of Atlantic highlands, 

 which slowly increases to the southward, until in the region to the east 

 of Philadelphia they have increased to over 25 feet. Beyond that point 

 they increase more rapidly throughout the southern counties, reaching 

 50 feet in Gloucester county and fully 80 feet in the vicinity of Salem. 

 In Delaware and in the eastern counties of Maryland they are between 

 30 and 40 feet, but on the western shore of the Chesapeake they cannot 

 be sufficiently well differentiated to be separated from the overlying 

 members. Thev have often been confused with the Redbank sands, 

 which overlie the marls. 



Navesink marls. — These marls, embracing the Lower Marl bed of 

 Cook, extend with a remarkably constant thickness of from 40 to 50 feet 

 from the Highlands of Navesink ^through out Monmouth and northern 

 Burlington counties, beyond which they cannot be very w T ell differen- 

 tiated from the overlying Redbank sands until eastern Maryland is 

 reached, where the two members reappear, although the marls are of 

 very much less thickness, generally not exceeding 12 feet. The Navesink 

 marls are typically glauconitic sands which themselves admit of further 

 subdivision throughout much of Monmouth county. The basal portion 

 consists generally of arenaceous beds that have been hitherto referred 

 to under the name of sand marl and which are generally highly fossil- 

 iferous wherever found. A great variety of fossil species has been ob- 

 tained from this horizon. Above the sand marl, in the northern por- 

 tion of the area, is a very compact blue marl which is highly glauconitic 

 and frequently fossiliferous in its central portions, a firm shelly layer 

 at times resulting (plate 46). The upper portion of the Navesink marls 

 is commonly more micaceous, and just at the top is at times quite 

 sandy. Farther to the south, in central and southern New Jersey and 

 in Delaware, the Navesink marls become much more argillaceous, the 

 glauconite being much reduced in amount. Whether the argillaceous 

 marls throughout this district represent the Navesink marls alone, or a 

 part or all of the Redbank sands as well, cannot be altogether satisfac- 

 torily determined. If unconformity exists, as seems probable.it is even 

 possible that these argillaceous marls may not in all cases even represent 

 the full development of the Navesink in the north. The changes which 

 have taken place in the materials makes it difficult to say just how much 

 of the middle and upper Monmouth should be included. 



Redbank sands. — These sands, comprising the Red sand of Cook, are 

 most typically developed in the region about Redbank, Monmouth 

 county, and in the highlands forming the Cretaceous escarpment in the 

 region to the north and west of that town. Throughout most of Mon- 



