MARYLAND GEOLOGICAL SURVEY IxXl 



belonging to both the Lafayette and Columbia formations, while south 

 of the diagonal line the Calvert formation occupies the base of the 

 sections and is overlain with sands and clays belonging to the Chop- 

 tank formation, the next succeeding member of the Chesapeake Group. 

 The northern and southern margins of the Calvert formation, or 

 the line of its contact with older and younger beds respectively, are not 

 in all places definitely known. The heavy mantle of Lafayette and 

 Columbia gravels makes it impossible to locate it accurately in all 

 places, but enough contacts have been discovered to establish its posi- 

 tion in many instances and to render the calculation of its presence 

 possible in others. 



Strike, Dip and Thichness 



The strike of the Calvert formation is in general from northeast to 

 southwest, but due to erosion and change in topography the outcrop 

 frequently becomes very sinuous and the strike apparently changes. 

 Thus on the Eastern Shore, where the country is low and very flat 

 and has been little dissected by streams, the outcrop is regular and 

 approximately coincides with the strike. But on the Western Shore 

 the country is higher and the 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 and Nomini cliffs, 

 there are no good places for examining the dip and as it must be 

 calculated as a whole over extensive regions, slight changes which may 

 occur in the dip are not often brought to light. 



The full thickness of the Calvert formation has been nowhere actu- 

 ally observed. The formation has been diagonally truncated above by 

 the Choptank and younger formations under which it lies uncon- 

 formably, so that in the region of Davidsonville the Calvert formation 

 shows only about 50 feet in thickness. We are fortunate in possessing 

 a reliable well-record at Crisfield in Somerset county, which passes 

 through the entire thickness of Miocene strata. In this well, the 

 thickness of the Calvert formation is apparently about 310 feet. Located 

 as this is in the extreme southern portion of the state and well 



