72 THE GEOLOGY OF CALVERT COUNTY 



Strike, Dip and Thickness. 



The strike of the Calvert formation is in general from northeast 

 to southwest, but the outcrop frequently becomes very sinuous, because 

 of erosion and changes in topography. Thus in the northern portion 

 of the county streams have carved out deep valleys, producing a most 

 irregular outcrop, which departs widely from the direction of strike. 



The dip is, as a whole, about 11 feet to the mile toward the south- 

 east. Apart from the exposures on the Calvert Cliffs of this county 

 and the Nomini Cliffs of Virginia, there are no good localities for 

 determiniUig the dip, and as it must be calculated as a whole over 

 extensive regions, many of them beyond the borders of the county, 

 slight changes which may occur are not often brought to light. 



The Calvert formation occupies the higher portions of the stream 

 valleys throughout the northern part of the county and gradually 

 dips to lower and lower levels as it passes toward the southeast until 

 it sinks beneath tide level. The line along which it finally disappears 

 in Calvert County extends, as indicated above, from the mouth of Ben 

 Creek to a point on Calvert Cliffs midway between Governor Eun 

 and Flag Pond. In the northern part of tlie county, then, the streams 

 cut through the basal members of the formation, while in the southern 

 part the deepest stream valleys reach only the upper members of the 

 formation, wliile the shallow drainage ways do not cut low enough to 

 uncover it, but have only sunk their valleys into the later formations of 

 the Chesapeake Group. 



The full thickness of the Calvert formation within the borders of 

 the county has nowhere been actually observed. It has been diagon- 

 ally truncated above by the Choptank and younger forma- 

 tiojis, under which it lies unconformably so that in the region of 

 Davidsonville, in Anne Arundel County, it has a thickness of about 

 50 feet. From this point it thickens rapidly down the dip until at 

 Crisfield, in Somerset County, it shows a thickness of about 310 feet 

 in an artesian well. From various calculations it appears that the 

 average thickness in Calvert County is about 150 feet. 



