20 THE RARITAN FLORA. 



tact, while usually deeply buried, is shown at a few localities 

 in Middlesex County and is frequently encountered in well bor- 

 ings. South of Trenton the basal Raritan beds, in the absence 

 of the Triassic, lie unconformably on the Philadelphia gneiss, or 

 schist. The thickness of the formation varies considerably. 

 Toward the northeast it is probably in the neighborhood of 

 260 feet, while just south of Trenton it is probably not over 

 half that thickness. In a well boring in Delaware, a much (cf. 

 Ft. Dupont) greater thickness has been encountered, but it 

 must be admitted that the correlation of this section possesses 

 considerable uncertainty. There seems to be evidence of a con- 

 siderable thickening down the dip, if the well records can be 

 relied upon. What the original thickness of the Raritan for- 

 mation was is conjectural. It is certain, however, that post-Rari- 

 tan erosion has removed much material. 



At the close of Raritan sedimentation, the region was suffi- 

 ciently elevated for erosion to attack the Raritan materials. 

 This interval was not of long duration, however, when meas- 

 ured by geological standards, and the land was soon under water 

 again, receiving the sediments that make up the Magothy for- 

 mation and which toward their close mark the inauguration of 

 true marine conditions, which became widespread in the suc- 

 ceeding formations of the Upper Cretaceous. 



CORRE1.AT10N. 



Passing over the somewhat diverse views of the older writers 

 who were inclined to regard the Raritan as of Jurassic age,^ 

 we find Prof. Newberry, in 1890, recognizing the .Am boy Clays 

 as Cenomanian^ in age and synchronous wdth the Dakota Group 



^ This age was also claimed for it by the late Prof. Marsh in several papers 

 published a score of years ago. 

 * In continental Europe the Cretaceous system is divided as follows : 



Danian. 



Senonian. 



Turonian. 



Cenonianian. 

 Unconformity. 



Albian. 



Aptian. 



Barremian. 



Neocomian. 



Upper Cretaceous. ' 



Lower Cretaceous. ' 



