NORTHERN EXPOSURES OF THE PAMUNKEY. 441 



creek to Mathias point. The finest exposures are in the high bluffs that 

 extend eastward along the river from the mouth of Acquia creek. About 

 100 feet of Pamunkey beds are exhibited, consisting mainly of glauconitic 

 marls and sands, with several limestone beds, and, near the top, a few feet 

 of light-colored sandy clays. Fossils are abundant, and very nearly the 

 entire Pamunkey fauna is represented. West of this region the weathered 

 phase of the formation predominates, and its soft buff sands are conspicuous 

 toward Stafford Court-House, in one area including a thick fossiliferous 

 limestone stratum. 



On the eastern side of the Potomac, Port Tobacco river, and Mattawoman, 

 Piscataway and Henson creeks and their branches give frequent exposures 

 of fossiliferous glauconitic marls, and there are outcrops along the Potomac 

 river at Pope's creek, at Clifton Beach and in the bluff at Fort Washington. 



Opposite Washington (as shown in figure 1, page 435) the western edge of 

 the formation is cut out and replaced by the Chesapeake formation. This 

 condition prevails in the high ridge lying just east of the Anacostia river ; 

 but farther eastward and southward the edge of the formation is exposed 

 again, and its fossiliferous marls are found in every drainage way to within 

 about five miles of the capital. 



Patuxent River. — In this valley the formation emerges from beneath the 

 Chesapeake beds at tidedevel a few miles below Nottingham, and, rapidly 

 widening in area northward, finally extends around past Marlboro to the 

 drainage of the Anacostia and northeastward to the shores of Chesapeake 

 bay. In the southern part of the area, dark-colored glauconitic marls pre- 

 vail ; but in districts where the Chesapeake mantle has been removed the 

 red sands of the weathered phase occupy the surface. These red sands con- 

 tain abundant casts and impressions of Eocene species, and there can be no 

 doubt as to their stratigraphic equivalency with the dark beds southward. 



Chesapeake Bay. — In the Annapolis region and along the South and 

 Severn rivers the weathered phase attains the greatest development, and red 

 sands with ferruginous crusts, concretions and sandstone layers occupy a 

 wide area. The opposite or " eastern shore " of Maryland is heavily mantled 

 by sands and gravels of undetermined age, and outcrops of the subterrane 

 are infrequent ; but I have studied the river banks and traced the Pamun- 

 key formation up the Chester river past Chestertown and up the Sassafras 

 river past Georgetown into Delaware nearly to Nockimixon pond, where it 

 thins out and the Severn and Chesapeake formations come together. 



In the "eastern shore" exposures the weathered phase was found to pre- 

 vail; but casts and impressions of Cardita planicosta and Dochiiopsis meekii 

 occur in every outcrop. On the Sassafras river the Severn formation occurs 

 for some distance near its mouth, and again, I believe, at its head ; but there 

 is a wide intermediate belt occupied by Pamunkey beds, which are espe- 



