50 THE RARITAN FLORA. 



istic fossils of the Magothy and allied Upper Cretaceous forma- 

 tions over a wide area. This is interpreted as due to the gradual 

 evolution of the Raritah flora, and does not seem of sufficient 

 weight to warrant the uniting of the Upper Raritan beds with 

 the Magothy formation, since, as previously mentioned, some of 

 Newberry's data are questionable, and the onlv well-marked stra- 

 tigraphic break occurs above the South Amboy plant horizon at 

 the eroded summit of the Amboy stoneware clay. 



ORIGIN AND RADIATION. 



A great many of the Raritan species appeared at approxi- 

 mately the same time in the western interior, the Arctic regions 

 and central Europe. The fact that these floras are all so different 

 from those of Lower Cretaceous age and that they contain so 

 predominating an element of dicotyledonous plants renders any 

 inquiry into their place of origin or their ancestral forms a sub- 

 ject of surpassing interest. 



There are no adequate data for a phylogenetic discussion which 

 is not purely speculative, the present desideratum being a knowl- 

 edge of those primitive forms from the Older Potomac and an 

 acquaintance with the flora which flourished while the Schooley 

 peneplain was being developed. 



A number of the immediate ancestors of Raritan species are, 

 however, represented in the flora of the Patapsco formation of 

 Maryland and Virginia, others are undoubted immigrants from 

 elsewhere. Where did this mid-Cretaceous flora take its origin? 

 A number of answers are suggested. First, it may have origi- 

 nated in eastern or central Asia, which is an old continental mass, 

 and spread from there westward into Europe and northeastward 

 into the Arctic regions and North America. As pre^'iously men- 

 tioned, it is recorded from Europe, America and the Arctic 

 regions. It may have originated in Europe and migrated from 

 thence across the Arctic to America, or it nia.y have originated 

 in America and mig"rated in a reverse direction. The somewhat 

 earlier appearance of more modern types toward the close of the 

 Lower Cretaceous and the somewhat more advanced organiza- 

 tion of the L^pper Cretaceous floras of America as compared with 

 those of Europe renders the fornier supposition improbable 



