88 THE GEOLOGY OF ST. ilARY S COUXTY 



the Lafa_yette formation might be considered as indicative of river banks. 

 On the southeast side of these outliers, where they face toward the 

 Sunderland sea, there is no opposing bank, but they drop away to the 

 Sunderland surface, which is unobstructed by other prominences toward 

 the southeast. It is evident that these outliers were once portions of 

 the mainland and that the narrow flats which ramify among them were 

 formerly stream valleys cut in the body of the Lafayette formation, 

 but with the advance of the Sunderland sea these drainage ways were 

 submerged and filled and the divides which separated them were either 

 submerged or else cut up into a series of outlying islands. A similar 

 topography may be seen on the Eastern Shore of Chesapeake Bay 

 to-day. 



Another line of evidence is furnished by the presence of a beach 

 gravel on the surface of the Sunderland formation as it approaches the 

 base of the Sunderland-Wicomico scarp. The Lafayette in this region 

 carries very little gravel and waves cannot produce a shingle beach 

 unless there is gravel at hand out of which to make it. At Charlotte 

 Hall the waves of the Sunderland sea concentrated on the beach the 

 small amount of gravel which they secured by the erosion"of the Lafayette 

 scarp. It may also be added that there are ice-borne blocks in the body 

 of the Sunderland formation beneath the scarp-line, but none have yet 

 been discovered in the Lafayette formation above. 



An even more significant feature of the topography in the vicinity 

 of Charlotte Hall is furnished by two generations of stream valleys. 

 One of these, the older, is now dry and unoccupied. It penetrates the 

 Lafayette formation and formerly drained from it into the Sunderland 

 sea. The other generation of valleys are now being rapidly extended 

 inland from the Patuxent and Potomac rivers. They are steep-walled 

 and V-shaped and at the present time have worked their way so far 

 back on the divide as to drain the edge of the Sunderland formation 

 in the vicinity of Charlotte Hall. These two valley streams not only 

 are distinct in age, but they have no physical connection whatsoever. 



In almost every place where good sections of Pleistocene materials are 

 exposed the deposit from base to top seems to be a unit. In other places. 



