220 PHYSIOGRAPHY AND GEOLOGY OP THE COASTAL PLAIN PROVINCE. 



also developed. At this time the shore-line seems to have been farther to the 

 east, and the present submerged channels of the continental shelf were 

 probably eroded during this interval. The Coastal Plain portion of the 

 Delaware Kiver with its extension as Delaware Bay; the Chesapeake Bay 

 and the tidal portions of the Potomac, Eappahannock, York, James, as well 

 as many smaller streams date from this post-Lafayette uplift. The atti- 

 tude of the subsequent deposits makes this evident, for the Sunderland, 

 Wicomico, Talbot, and Recent terrace formations surround, and in all cases 

 slope toward these various water ways. The Lafayette formation was cut 

 through in most places by the streams, and valleys were opened up in the 

 older deposits, several of which became many miles wide before the corrasive 

 power of the streams was checked by the Sunderland submergence. 



Sunderland stage. — As the Coastal Plain was depressed during the early 

 Pleistocene, the ocean waters gi'adually extended up the river valleys and 

 then over the lower-lying portions of the stream divides. The waves 

 working on the Lafayette-covered divides, removed the mantle of loose 

 materials and either deposited the debris farther out in the ocean or 

 dropped it in the estuaries produced by the drowning of the lower courses 

 of the streams. Sea clifPs produced on points exposed to wave action were 

 gradually pushed back as long as the sea continued to advance. These now 

 represent the escarpments separating the Sunderland from the Lafayette. 

 The materials which tlie -waves gathered from the shore, together with 

 other materials brought in by the streams, were spread out in estuaries and 

 form the Sunderland formation. The tendency was to destroy all irregular- 

 ities produced during the post-Lafayette erosion interval. In many places 

 undoubtedly old stream courses were obliterated but the channels of the 

 larger streams, while in some cases entirely filled, were in the main left 

 lower than the surrounding regions. Thus in the uplift following Sunder- 

 land deposition the larger streams practically reoccupied the same channels 

 they had carved out in the preceding erosion period. They at once began 

 to clear their channels and to widen their valleys so that when the next 

 submergence occurred the streams were cutting as before in Tertiary and 

 Cretaceous materials. On the divides, also, the Sunderland was gradually 

 undermined and worn back. 



^Vicomico stage. — After the Coastal Plain had been above water for a 

 considerable interval a gradual submergence again occurred permitting the 

 ocean waters to encroach on the land. This submergence seems to have 

 been about equal throughout the Coastal Plain. The sea did not advance 



