MARYLAND GEOLOGICAL SURVEY 91 



unconformity. These breaks commonly disappear in short distances 

 showing probably that they are for the most part only local phenomena 

 within the same formation, produced by the contemporaneous removal of 

 material by shifting, shallow-water currents. They generally seem to 

 have no relation to each other in closely adjoining regions as far as can be 

 recognized. Since the Pleistocene formations occupy so nearly a hori- 

 zontal position it should be possible to connect these separation lines if 

 they were subaerial erosional unconformities. In the absence of any 

 definite evidence showing these lines to be stratigraphic breaks separating 

 two formations, they have been disregarded in the mapping. 



Yet it is not improbable that in some places the waves of the advancing 

 sea in Sunderland, Wicomico, and Talbot times did not entirely remove 

 the beds of the preceding period of deposition over the area covered by 

 the sea in its next transgression. Especially would deposits laid down 

 in earlier drainage lines as the sea advanced be likely to persist as isolated 

 remnants which later were covered by the next mantle of Pleistocene 

 materials. If this is the case each formation from the Lafayette to the 

 Wicomico is probably represented by fragmentary deposits beneath the 

 later Pleistocene formations. Thus in certain sections the lower portions 

 may represent an earlier period of deposition than that of the overlying 

 beds. In those regions where the Miocene or older materials are not 

 exposed in the base of the escarpments each Pleistocene formation near 

 its inner margin probably rests upon the attenuated edges of the next 

 older formation. Since lithologic differences furnish insufficient criteria 

 for separation of these late deposits, and sections are not numerous enough 

 to distinguish between local interformational breaks and widespread 

 unconformities resulting from an erosion interval, the whole mantle of 

 Pleistocene materials occurring at any one point is referred to the same 

 formation. Even if the stratigraphic relations could be determined the 

 areas of outcrop of the subjacent materials exposed in the present stream 

 channels would hardly admit of cartographic representation. For ex- 

 ample, the Sunderland is described as overlying the Jurassic ( ?), Creta- 

 ceous, Eocene and Miocene deposits and extending from the base of the 

 Lafayette-Sunderland escarpment to the base of the Sunderland-Wicomico 



