MARYLAND GEOLOGICAL SURVEY 63 



rapidly remove the materials wliich the Lafayette sea had but just 

 deposited. 



The salient features of the Coastal Plain as a whole, as well as those 

 of St. Mary's Coimty, were outlined at this time, although they do 

 not appear to have received their full strength and final touches until 

 after the close of the Talbot stage. It is probable that the valleys of 

 the Potomac and Patuxent rivers, together with their larger tributaries, 

 were cut at this time, and that the trough in which Chesapeake Bay 

 now lies was also excavated by the Susquehanna Eiver, which flowed 

 down from the north and out to the ocean somewhere in the vicinity 

 of the present outlet of Chesapeake Bay. It is not probable that at 

 this time these depressions were cut to their present depth. They have 

 apparently been deepened during each successive uplift. 



At the close of the post-Lafayette elevation the terrace which the 

 Lafayette sea had deposited had suffered considerably from erosion, and 

 had been so largely removed from St. Mary's County that large areas of 

 the underlying miocene deposits were exposed. On this surface the 

 Sunderland sea advanced when the region sank once more beneath the 

 ocean. The depression during this subsidence was not as great as during 

 the Lafayette stage, although when it had reached its maximum the 

 county was again submerged with the exception of a few islands near 

 Charlotte Hall. The appearance of the region during this maximum 

 subsidence is shown in Fig. 1. 



THE WICOMICO STAGE. 



As the region slowly rose above the waves, the terrace which had 

 just been deposited by the Sunderland sea was gradually elevated to 

 dry land and now forms the main divide of the county. As this surface 

 gradually appeared above the ocean, it was vigorously attacked by sub- 

 aerial erosion and much of it was destroyed by the rivers, which rapidly 

 advanced their valleys across it. After the county had stood for some 

 time above the ocean, it was again depressed to receive the waters of 



