MARYLAND GEOLOGICAL SURVEY 73 



Areal Distribution. 

 The Choptank formation, which constitutes the second member of 

 the Chesapeake Group in Maryland and lies immediately above the 

 Calvert formation, is found in Caroline, Talbot, and Dorchester counties, 

 on the Eastern Shore, and Anne Arundel, Calvert, Prince George's, 

 Charles, and St. Mary's counties on the Western Shore. 



Strike, Dip and Thickness. 



The strike of the Choptank formation is in general from northeast 

 to southwest; but because of erosion, j^articularly on the Western Shore, 

 as pointed out above, the outcrop is very sinuous and the strike appears 

 to change locally. 



The dip does not appear to be constant throughout the entire extent 

 of the formation. In Calvert County, where the Choptank is best 

 exposed, the northern portion of the formation down to Parkers Creek 

 seems to lie almost horizontal; but south of this point the base of the 

 formation dips away at about 10 feet to the mile. Because of this 

 structure, the Choptank formation occupies hilltops in the northern por- 

 tion of its area and gradually occupies lower and lower levels, until in 

 the southern portion of its area it is found in river bottoms and finally 

 disappears beneath tide. The best place to examine the dip of the 

 Choptank formation is along the Calvert Cliffs between Parker Creek 

 and Point of Eocks. Here an almost unbroken exposure may be seen 

 dipping gradually toward the southeast. 



The thickness is variable. In the Nomini Cliffs, Virginia, it is 

 present as a 50-foot bed between the Calvert formation below and the 

 St. Mary's formation above. This is the thickest exposure which is 

 open to direct observation. In the well section at Crisfield, mentioned 

 above in connection with the Calvert formation, the Choptank forma- 

 tion attains a thickness of about 175 feet. It will thus be seen that 

 like the Calvert, it thickens as it passes down the dip. The average 

 thickness in St. Mary's County appears to be about 112 feet. 

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