108 THE GEOLOGY OF PRINCE GEOKGe's COUNTY 



above it unconforiiiably. Fortunately, a reliable well record at 

 Ch'isfiekl, Somerset County, exhibits the entire thickness of Miocene 

 strata. In this well the Calvert formation is apparently about 300 

 feet thick. As this well is located in the extreme southern portion 

 of the State and far down the dip, there is probably a rapid thicken- 

 ing; of this formation as it passes to the southeast toward the ocean. 

 At Chesapeake Beach, on the bay shore in Calvert County, a well 

 which begins in the Calvert formation a little above tide passes out 

 of it and into the Eocene at a depth of 60 feet ; at Centerville it is 

 found at a depth of 81 feet and is 65 feet thick; at Crisfield the 

 formation lies 465 feet below the surface. 



Stratigrapliic BeJations. — Xear the Maryland-Delaware border 

 the Calvert rests unconformably u}X)n one of the Cretaceous forma- 

 tions (Rancocas). Farther southwest it overlies the Aquia forma- 

 tion, and in southern Maryland it lies unconformably upon the 

 Xanjemoy, a relationship which shows the gradual transgression of 

 the Miocene deposits southwestward. In this county it lies uncon- 

 formably upon the I^anjemoy, Aquia, or Matawan formations and 

 is overlain unconformably by deposits belonging to the Lafayette or 

 Pleistocene. 



Suhdi visions. — The Calvert formation has been divided into two 

 meml)ers, known as the Fairhaven diatomaceous earth and the Plum 

 Point marls. These are more fully described in the above-mentioned 

 report on the Miocene of Maryland. 



The Fairhaven diatomaceous earth lies at the base of the forma- 

 tion and is characterized by the presence of a large proportion of 

 diatoms embedded in a very finely divided quartz matrix. Calcar- 

 eous material is present in this bed in only very small amounts. 

 Besides diatoms, there are other Miocene fossils, usually in the form 

 of casts, and organic remains reworked from the underlying Eocene 

 beds. The name for this member is derived from Fairhaven, Anne 

 Arundel County, wliere the beds are well developed. 



The contact of the diatomaceous earth with the Eocene beds lies 

 about 2 feet l)eneath a band of sandstone from 1 to 8 inches thick, 



