134 THE PLIOCENE AND PLEISTOCENE DEPOSITS OF MARYLAND 



how portions of the ocean bed, which were formerly bathed by salt water 

 and sustained a marine fauna, are now converted to lagoons behind bar- 

 rier beaches and have passed over in varying degrees to brackish-water 

 conditions bearing estuarine faunas. 



Another elevation of the region brought the Talbot epoch to a close. 

 During the erosion which followed, the Coastal Plain received its final 

 touches to the topography which it now exhibits. Water ways which had 

 been deepened through each successive uplift were now cut still deeper. 

 The ocean retreated across the continental shelf to a point far beyond 

 the present shore line and the Susquehanna river received as tributaries 

 the streams from both banks and flowed the length of Chesapeake Bay 

 out through the Capes to the Atlantic ocean beyond (Plate XXXI). 

 Active erosion began once more, but before it had proceeded far, the re- 

 gion sank to its present position, the sea took possession of the lower 

 Susquehanna valley and transformed it to the Chesapeake Bay and its 

 estuaries, imparting to the region its present aspect. When this down- 

 ward movement will cease or how extensive will be the changes which it 

 is destined to produce, no one can say. It is only known that this is 

 the latest of a long series of oscillations and that the region still appears 

 to be sinking. 



A few words may be added regarding the successive uplifts and de- 

 pressions which have taken place in the Coastal Plain from Lafayette 

 down to Eecent time. A much simpler explanation would doubtless be 

 afforded by concluding that these various terraces were deposited during 

 pauses in one general uplift. There are certain facts, however, which 

 show that such a simple explanation is impossible. These have all been 

 presented above, but may be briefly summarized here. 



First. With the exception of the Lafayette, the surface of each of the 

 terrace formations is found to extend up valley reentrants which pene- 

 trate the body of the terrace next above. Examination has shown that 

 this surface is not due to sedimentation without the valley and to cut- 

 ting within, but to sedimentation outside and inside as well. In other 

 words, the building of the terraces beneath the scarp was accompanied by 

 the filling of valleys within the body of the formation. Had there been 



