LOCATION OF POTOMAC REDS. 45 



seen by Professor Rogers. About four miles higher up the river there is 

 another outcrop of a few feet of Potouiiic in the base of the river bank. 

 This was seen by Professor Rogers. In botli phices the material is a coarse 

 sand of brownish-gray color, which contains manv pebbles, some of which 

 are three inches in diameter. At the bridge occur balls of dark gray clay 

 of a foot or more in diameter, which, as in the areas farther nortli, are 

 embedded in the i)ebbly sand. The two exposures considered alone indi- 

 cate here an area only four miles long; but the coarse pebbly character of 

 the sand, taken with the fact that oidy the top is shown, seems to show that 

 this, which may be called the Nottoway area, is nuich more extensive. 

 The river in cutting down has evidenth- barely reached the top of the for- 

 mation. 



As the Potomac of the Nottoway area in the most important points 

 possesses exactly the same features as those of the more northern areas, 

 there can be little doubt that, if we could trace each of the areas eastward, 

 we should fiiul them uniting to form one continuous terrane extending from 

 north of Baltimore to the Nottowa}'. South of the Nottoway unequivocal 

 Potomac has not been seen. In portions of Greenville County some of 

 the Appomattox beds are strikingly like the pebbly sand of the Potomac, 

 and indeed seem to be composed of the debris of Potomac strata but little 

 modified. This ma}' explain the announcement of the existence of the for- 

 mation in this part of Mrgiuia made by Professor Rogers in his earliest 

 reports, but not repeated in his later ones. 



Until the Roanoke at Weldon is reached the streams do not seem to 

 have cut down through the Tertiary, and hence they do not reacli the 

 horizon of the Potomac. The Roanoke, however, at Weldon, in North 

 Carolina, has cut down to the Azoic rock, but it is dilHcult to find expo.s- 

 ures at the level where the Potomac may ])e looked for. The river in 

 flood deposits a large amount of mud on its banks and in the channels of 

 the creeks emptying into it, and this hides everything. Except immedi- 

 ately on the river a thick covering of the Appomattox formation here, as 

 everywhere south of the Nottoway, conceals even the Eocene and Miocene 

 beds. At ^Veldon, near the noi-th end of the railroad bridge, a small 

 stream, a mere spring branch, flows at a low level into the Roanoke. Over 



