70 the geology of calvert county 



The Miocene. 

 The Chesapeake Group. 



The Miocene deposits of the Middle Atlantic slope have been de- 

 scribed under the name of the Chesapeake Gronp. In Maryland, the 

 materials which compose the formations of this group consist of clay, 

 sandy-clay, sand, marl and diatomaceous earth. The sand3'-clay mem- 

 bers are, when freshly exposed, greenish to greenish-bhie but slowly 

 change under the influence of the weather to a slate or drab color. 

 As the Miocene beds contain but little glauconite, it is not a difficult 

 task on the basis of lithologic criteria to separate them from the Eocene 

 deposits, and they are still more readily distinguished from the Columbia 

 loams and gravels above. 



It has been found possible to separate the beds of the Chesapeake 

 Group into three formations, which are designated, beginning with 

 the oldest, the Calvert formation, the Choptank formation and the 

 St. Mary's formation. 



THE CALVERT FORMATION, 



Calvert County has suggested the name for this formation because 

 of its typical development there. In the famous Calvert Cliffs along 

 the eastern border of this county the waves of Chesapeake Bay have 

 cut an almost unbroken exposure rising nearly 100 feet in height and 

 extending from Chesapeake Beach to Drum Point, a distance of about 

 30 miles. 



Areal Dktrihution. 



The Calvert formation wliich lies at the base of the Chesapeake Group 

 in Maryland crosses the state from northeast to southwest. On the 

 Eastern Shore it is found in the southeastern corner of Kent County, 

 throughout almost the entire extent of Queen Anne's County and the' 

 northern portions of Talbot and Caroline counties. 



On the "Western Shore the Calvert formation is found extensively 

 developed in Anne Arundel, Prince George's, Charles, Calvert, and St. 

 Mary's counties. It appears as a long line of outcrop extending from 

 the hills near the head of South River estuary to a place on the Calvert 



