OLDER POTOMAC OF VIRGINIA AND MARYLAND. 569 



The species peculiar to the Baltimore beds are the following : 



Acrostichopteris longipennis, with 57 specimens. 

 Celastrophjrlhim latifolium, with 11 specimens. 

 Celastrophylhim obovatum, with 17 specimens. 

 Protesephylkim dentatum, with 15 specimens. 

 Vitipliyllum multifidum, witli 150 specimens. 

 VitiphylKmi parvifohum, witli 7 specimens. 



Of less importance are the new species: 



Adiantites jjarvifolius, with 1 specimen. 

 Plantaginopsis marylandica, with 5 specimens. 



It should be noted, as indicating a Rappahannock age for the beds, 

 that the only species of the genus Vitiph^dlum found outside of the 

 Maryland localities occurs in the Rappahannock beds at the locality 

 Roadside near Potomac Run, in Virginia. It is very rare here. It 

 is also noteworthy that the most characteristic plants of the Aquia 

 Creek beds in Virginia and at Fort Foote, such as the different species 

 of Sapindopsis, are wholly wanting. Sapindopsis is so abundant in 

 the Aquia Creek beds that its absence is a strong indication that, where 

 this occurs, the strata are not of Aquia Creek age. The peculiar species 

 of Populus, Protesephyllum, etc., so characteristic of the Mount Vernon 

 strata, are also absent. This gives a presumption that the Baltimore 

 strata are not of Mount Vernon age. 



I was for a time of the opinion that these Baltimore beds are a 

 peculiar phase of the Aquia Creek series. This conclusion was reached 

 from the fact that they contain so many dicotyledons having an aspect 

 different from that of the archaic Ficophyllums, Proteseph3dlums, etc., 

 of the Rappahannock, while these are mostly absent. Pointing to the 

 same conclusion was also the fact that other characteristic types of the 

 Rappahannock are wanting, or but feebly represented. The dicotyle- 

 donSj although strongly represented, are still very peculiar and archaic, 

 and the more modern forms of the Mount Vernon and Aquia Creek 

 are wholly wanting. On the whole, it may be stated that the balance 

 of evidence is strongly in favor of the Rappahannock age of the beds. 

 When we take into consideration the character of the rock material, 

 it may be concluded that they belong to the Arundel member of the 

 subdivision made by the Maryland Survey. 



