130 W. J. McGee — Three Formations of 



more, as well as on the Patuxent and Patapsco rivers and their 

 tributaries, the lower division is exposed and occasionally yields 

 plant remains closely allied to those found in Yirginia. 



Both members of the formation appear in the precipitous 

 shores of the head of Chesapeake bay, the sandstone only on 

 the north, but the white, blue, purple and varigated clays on 

 both east and west ; and along Sassafras river these clays are 

 unconformably overlain by the pyritous clays and greensands 

 of the Maryland Cretaceous. Identifiable fossils have not been 

 found in the sandstone member at this locality ; but a few 

 plant remains were found in the clays. The magnificent ex- 

 posures of both the Potomac and Columbia formations here 

 are described in detail and fully illustrated elsewhere.* 



Extensive outliers of gravel occur on both sides of the Sus- 

 quehanna several miles from the body of the formation, notably 

 at Webster on the south and "Woodlawn (or Battle Swamp) on 

 the north of the river. 



In extreme northeastern Maryland and in northern Dela- 

 ware the sandstone member of the formation is not exposed as 

 a continuous body, though it is represented by occasional iso- 

 lated outliers of gravel upon the marginal Piedmont hills ; but 

 the superjacent clays appear in a number of localities, and form 

 the subterrane over a considerable zone parallel with the Pied- 

 mont escarpment. They have been studied by Chester, who 

 designates them " Plastic Clays," and refers them to the "Lower 

 Cretaceous ("Wealdon ?)."f 



So between the Rappahannock and the Brandywine the for- 

 mation is a continuous terrane, consisting of a series of clays 

 reposing perhaps unconformably upon a series of sands and 

 gravels, while outliers of the inferior division crown the crests 

 of the Piedmont plateau many miles from the main body ; but 

 northward it contracts and is again represented only by isolated 

 remnants and exposures. 



In southeastern Pennsylvania both members of the forma- 

 tion have been recognized by different geologists and have been 

 variously classed. Clays apparently representing the upper 

 member occur in the northeastern part of Philadelphia county 

 where they have been referred to the Wealden ;J the gravelly 

 outliers representing the lower member in the vicinity of Phil- 

 adelphia have been designated the " Bryn Mawr Gravel " (from 

 a locality of typical outcrop) and referred to the Tertiary by 

 Lewis ;§ and similar exposures in Delaware county have been 



* " Notes on the Geology of the Head of the Chesapeake Bay," 7th Ann. Rep. 

 XT. S. Geol. Survey (in press). 



fProc. Acad. Nat. ScL, 1884, 250-1. 



\ 2nd Geol. Surv. Pa., Report X, Hand Atlas of Pa., J. P. Lesley, 1885, 

 Plate 46. 



§Proc. Acad. Nat. Sci. Phil., xxxii, 180, 269, 272; Ibid. 296, et seq.; Journ. 

 Franklin Inst., xcv, 1803, 371-73; and elsewhere. 



