FLORA AND THE AGE OF RARITAN FORMATION 255 



Asplenium dicksonianum Heer Gleichenia zippei Heer 



Celastrophyllum hrittonianimi Hollick Podozamites knowltoni Berry 



Ficus myricoides Hollick Podozamites lanceolatus (L. & H.) Ft 

 Frenelopsis hoheneggeri (Ettings.) Braun 



Schenk Sequoia reichenbachi (Gein.) Heer 



Gleichenia giesekiana Heer Thuyites meriani Heer 

 Gleichenia inicromera Heer 



Of these the ferns and the gymnosperms which make up the bulk 

 of the list are to be regarded primarily as Lower Cretaceous types 

 which survived into the Upper Cretaceous, while the dicotyledons are 

 precursors of the Upper Cretaceous flora. Among the generic types 

 of ancient lineage which are represented in the Raritan are Baiera, 

 primarily a Triassic and Jurassic genus the Raritan species of which 

 is closely related to forms found in the Older Potomac, Williamsonia, 

 a Jurassic and Lower Cretaceous genus, Brachyphyllum, a Triassic 

 and Jurassic genus the Raritan species of which is closely related to, 

 and clearly descended from, Brachyphyllum crassicaule Font, of the 

 Patapsco formation, and finally Czekanowskia, a Triassic and Jurassic 

 (chiefly Oolitic) genus. 



In no part of the world has a single representative of any of these 

 genera been found as late as the Senonian and it is significant that 

 two of them, Brachyphyllum' and Czekanowskia, furnish their last 

 known record in the Cenomanian of Portugal while the last occurrence 

 of Baiera and Williamsonia^ is in the Cenomanian Atane beds of 

 Greenland. 



When the Raritan flora is compared in detail with the Patapsco 

 flora of Maryland and Virginia many common features are brought 

 out which at first sight tend to be obscured by the preponderating 

 dicotyledonous element in the former. In addition to the identical 

 or closely related forms previously mentioned we find among the 

 dicotyledons nine Raritan genera which make their first appearance 

 in the Patapsco. These are Aralia, Sassafras, Celastrophyllum, 



1 The Raritan species B. macrocarpum Newb. is recorded from the following 

 American horizons: Montana Group of Wyoming, Dakota Group of Kansas, Magothy 

 formation of Long Island, New Jersey, and Delaware, the Middendorf of South Caro- 

 lina ( ?), the Black Creek of North Carolina, the Tuscaloosa and Eutaw of Alabama, 

 and the Patoot beds of Greenland ( ?), the former of course of Senonian age. 



2 A questionable species is recorded from the Dakota Group and another species 

 occurs in the Magothy formation. 



