Maryland Geological Survey 85 



direction is evidenced by the varying character of the deposits and the 

 statigraphic relations which the several formations sustain to each 

 other. In the succeeding chapters the surface configuration, both of 

 the crystalline floor and of the Potomac Group is discussed, and some pos- 

 sible interpretations advanced. 



The greater thickness of the formations of the Potomac Group along 

 a belt somewhat to the eastward of the Fall-line may have emphasized 

 the downward movements in this portion of the Coastal Plain during 

 Potomac time. On the other hand, the gradual removal of the weight 

 over the Piedmont region by the removal of its residuals has possibly 

 occasioned an upward movement of that area as well as of immediately 

 adjacent Coastal Plain regions. The accumulating results of these ten- 

 dencies, particularly the first mentioned, from the beginning of Potomac 

 time until the present, have been the weakening of the crystalline floor 

 near the landward border of the Coastal Plain, accompanied by monoclinal 

 folding and even faulting on a limited scale. The studies of McGee in 

 the upper Chesapeake area, and of others to the northward and south- 

 ward, fully convinced him that displacement had actually occurred, al- 

 though no very definite evidence was adduced in demonstration of the 

 same. Other writers, including Fontaine, however, believe that we have 

 to do merely with sedimentation across a pre-Potomac escarpment. In 

 the opinion of the authors of this paper, the Fall-line phenomena in 

 Maryland, and elsewhere, afl'ord considerable evidence of actual dis- 

 placements. A number of carefully constructed vertical sections on a 

 large scale have been made across the Fall-line zone, and these show 

 in nearly every instance evidence of this. 



Evidence of the actual displacement in the Potomac beds is very 

 clearly defined in the vicinity of Eelay, Maryland, and this is further 

 strengthened by the fact that the Miocene beds at Catonsville, near by, 

 lie considerably higher than the normal dip of the main body of the 

 Miocene deposits calls for. 



At the openings of the Maryland Clay Company, at Northeast, Mary- 

 land, there occurs a well-defined example of an anticline in the Patuxent 

 beds which is believed by Ries to have been produced by the hydration 



