332 THE POTOMAC OE YOUNGER MESOZOIC FLOEA. 



member and the latter the upper member of the formation. When, then, 

 reference is made to Neocomian phxnts, fossils of the Wealden, Urgonian, 

 and Aptian groups are included and not distinguished. 



In the regions containing Potomac areas the older flora which conies 

 next to that of the Potomac beds is that described by me in Contributions 

 to the Knowledge of the older Mesozoic of Virginia (Mon. U. S. Geol. 

 Survey No. 6). This is Rhjetic in age. 



In Virginia, and as far north as the Potomac beds have been traced 

 and identified, if we except the doubtful location of the trunks of Tysonia 

 Manjlandica, no plants of any value in determining age have been found 

 in any Mesozoic strata above the lower Potomac. 



But in New Jersey a large number of well-preserved fossil plants have 

 been collected from the sands and clays that form the lowest member of the 

 Cretaceous of that State, and which are so largely worked at some localities 

 for the manufacture of fire-brick and pottery. These plants form the flora 

 which comes next above that of the lower Potomac beds, and possesses im- 

 portance in determining geological relations. 



The New Jersey fossils are being studied and described by Dr. New- 

 berry. Until his conclusions are published we must wait for a final deter- 

 mination of their age. It may, however, be stated here that these fossils 

 have been generally taken to be of nearly the age of those from the Dakota 

 group of the United States, or of the Cenomanian of Europe. 



The geological relations of the plant-bearing beds of New Jersey and 

 the upper Potomac, or mottled clay group of Maryland, have not been 

 determined, but, as has been stated before, these two groups will probably 

 prove to be of the same age. The two floras then with which that of the 

 lower Potomac may be compared as next preceding and following it, in the 

 areas where it is found, are the Rhsetic plants of Virginia and North Caro- 

 lina, and the probably upper Cretaceous New Jersey flora. The compari- 

 son with these is important, as showing on the one hand survivors from the 

 older flora, and on the other hand precursors for the younger. 



By the kindness of Dr. Newberry I have been enabled to see a large 

 number of drawings of the New Jersey plants. They show that the flora 

 of this formation is totally different from that of the lower Potomac. The 



