SURFACE CONFIGURATION 



211 



these phenomena is found in the hypothesis of incipient folding in 

 post-Potomac time. 



Surface Configuration of Potomac Group and its possible 



Interpretation 



The records of deep artesian well borings to the eastward of the Poto- 

 mac belt indicate some clearly defined irregularities in the rate of 

 decline of the Potomac surface. It will be seen from the following- 

 table that only a single record shows a greater decline than 25 feet, 

 while most of them show a descent much less than this amount, in one 

 instance (Crisfield) even less than the observed average landward dip 

 (12 J feet),of the Eocene deposits which immediately overlie the Poto- 

 mac beds to the southward. 















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Location of well. 



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istance 

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Miles. 



Feet. 



Feet. 



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Middletown, Delaware 



6 



7 



150± 

 240 



25+ 

 34 



302+ 



Rock Hall, Maryland 



Unknown 



Claiborne, Maryland 



19 

 24 



440. 

 430 



23 



18 



<t 



Tunis Mills, Maryland 



" 



Tilghmans island, Maryland 



27 



400 



15 



< < 



Gloucester Court- House, Virginia. . . . 



38 



600 



16 



t ( 



Williamsburg, Virginia 



88 



550+ 



14.5 



276+ 



North End point, Virginia 



62 



920 



15 



252 



Crisfield, Maryland 



9L 



964 



10.6 



1004- 





According to these records, there is a marked lessening in the decline 

 of the Potomac surface far to the seaward. There is even an actual 

 rise in this surface in the u Eastern shore " of Maryland and Delaware 

 between the Chester and Choptank rivers, although it again declines 

 eastward a little farther seaward, as shown by the boring at Gloucester 

 Court-House, Virginia. Whether we have to do with an erosional irreg- 

 ularity in the Potomac surface or with incipient deformation, the facts 

 at hand do not permit us to determine. If the irregularity is due to 

 the latter cause, the axis of the anticline would not seem to be coinci- 

 dent with that of the peninsula of Delaware, but would cross the latter 

 in a northeast-southwest direction. A depressed barrier such as has 



XXXI— Bull. Geol. Soc. Am., Vol. 13, 190L 



