OLDKi; POTOMAC OF XIKCIMA AND MAUVLAM). 509 



The species peculiar to llio Balliinoro l)ods arc the following: 



Acr()stich()]it('ris lougiju'iiiiis, with .'iT spccinu'u.s. 

 ('olasti'oplivlluin latifoliuin, \\illi II s|)('ciinen.s. 

 ('('last r()|)li\lluin (ilxivat uiii. \\\\\\ 17 spcciincii.s. 

 Prol('a'|)liylluin (Icntatuin. willi 1 •'> specimens. 

 Vil il)liyllimi iniilliliduin. willi 1 .')() speciiiien.s. 

 Nil ipli\ lliini par\ iloliiini. willi 7 s|)eciiiiens. 



< )t' less iiii|)(ii-l;iiic(> arc the new s|)cci('s: 



Adiaiililes parvil'olius, willi 1 spei'iineii. 

 l'laiilai;:iii()|)sis inarvlaiidica, with 5 speciiiH>ns. 



Il sliould he noted, as iiidicatiiifj; a K;ipj)ahannock age for the beds, 

 that the only species of the genus Vitipliylhim found (uitsidc of the 

 Maryland localities occui's in the Rappaliannock beds at the locality 

 Roadside neai' Potomac Run, in Virginia. It is \(n'y rai'(> here. It 

 is also notewoi'tli}- tliat the most characteristic ])lants of the Aquia 

 Creek beds in Virginia and at I'^ort Foote, such as the different species 

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

 the A(iuia Creek beds that its al)sence is a strong indication that, where 

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

 of Populus, Protea^phylhmi, etc., so characteristic of the Mount Vernon 

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

 sti'ata are not of Movmt Vernon age. 



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

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

 fi'om the fact that they contain so many dicotyledons having an aspect 

 differ(Mit from that of the archaic Ficophyllums, Protesephyllums, etc., 

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

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

 Rappahannock are wanting, or but feel^ly represented. The dicotyle- 

 dons, although sti'ongly represented, are still very peculiar and archaic, 

 and the more modern forms of the Mount \^ernon and Acjiiia Creek 

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

 of evidence is strongly in fn^•^n^ of the Rappahannock age of the beds. 

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

 it may l)e concluded that they belong to the .Vrundel member of the 

 subdivision made by the Marvland Survey. 



