OLDER POTOMAC OF VIRGINIA AND MARYLAND. 487 



FOSSIL PLAATS FKOM THE COLCHESTER UOAD. 



On August 5, 1893, Professor Ward obtained from the Colchester 

 road in Virginia eight fragments of shale with traces of fossil plants. 

 They are imprints of small portions of the ultimate pinnse of a fern 

 that resembles Thyrsopteris pachyrachis Font.," a plant previously 

 described from Virginia. There is not enough material sufficiently well 

 preserved to positively determine the species. This is a species charac- 

 teristic of the lower portion of the Lower Potomac, the part embraced 

 in Professor Ward's two subdivisions, the James River series and the 

 Rappahannock series. The exact locality from which these specimens 

 were obtained is the right bank of Pohick Creek, on the west side of 

 the Colchester road. This is a locality which at the time of the prepa- 

 ration of Monograph XV was not known to yield fossil plants. 



FOSSIL PLANTS FROM WHITE HOCSE BLUFF AND MOUNT VERNOX (BROOKE BEDSl. 



In the banks of the Potomac River called White House Bluff, and 

 up the river to near the Mount Vernon Mansion, there are two different 

 horizons containing fossil plants. The lower one is that of the Mount 

 Vernon series of strata, on which Professor Ward found Mount Vernon 

 plants at two localities. These will be noticed farther on (see p. 490). 

 The upper one belongs to the Aquia Creek series or Brooke beds, 

 and will be treated first because first discovered by me (see Monograph 

 XV, pp. 22-23). Later Professor Ward discovered a locality of this 

 age above the mouth of Doag Creek on the Mount Vernon estate. 

 It will be convenient to treat both these localities under one head. Mr. 

 William Hunter discovered in White House Bluff, near my original 

 locality, a new localit}^ for Aquia Creek plants. This is at the lower 

 or south end of the large exposure next below the original locality and 

 at nearly the same elevation above the water. These three localities 

 for Aquia Creek plants may for distinction in this paper be called "Fon- 

 taine's locality," "Hunter's known locality," and "Ward's locality." 



In 1895 Mr. Hunter collected a few specimens in this bluff from 

 another locality, whose position was not given. These plants show 



"Monograph XV, pp. 132, 133, pi. xlvi, figs. 3, 5; pi. xlvii, figs. 1, 2: pi. xlix, fig. 1. 



