Ixxii GEOLOGICAL AND PALEONTOLOGICAL RELATIONS 



down the dip, the data probably indicate a rapid thickening of 

 this formation as it passes southeast toward the ocean. At Cris- 

 field, the Calvert formation lies 465 feet below the surface of the 

 country, at Centerville it is found at a depth of 81 feet and is G5 

 feet thick, while 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 at a depth of 60 feet. 



The Calvert formation occupies the hilltops throughout the northern 

 portion of its area and gradually dips to lower and lower levels as it 

 passes toward the southeast until it finally sinks beneath tide level. 

 The line along which it finally disappears on the Western Shore is a 

 diagonal line extending from near Point of Rocks on Chesapeake Bay 

 through the mouth of Indian creek on the Patuxent to the mouth of 

 Wicomico river on the Potomac. On the Eastern Shore, as stated 

 above, the country is everywhere flat and no marked difference in eleva- 

 tion of the Calvert formation is discernible. 



Subdivisions. 



The Calvert formation cannot be readily divided throughout the 

 Eastern Shore, as it is so completely covered up by younger deposits 

 that the bipartite division if present there has not been observed. 

 On the Western Shore, however, the divisions are more clearly marked 

 and have been traced from Chesapeake Bay to the Potomac river. 

 The two divisions into which the Calvert formation falls are the Fair- 

 haven diatomaceous earth and the Plum Point marls. 



Fairhaven Diatomaceous Earth. — This member lies at the base 

 of the Calvert formation and is characterized by the presence of a large 

 proportion of diatoms imbedded in a very finely divided quartz matrix. 

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

 Beside diatoms, there are other Miocene fossils, usually in the form of 

 casts, and organic remains reworked from the underlying Eocene beds. 

 Fairhaven, Anne Arundel county, where the beds are well developed, 

 has suggested the name for this division. 



The contact of the diatomaceous earth with the Eocene beds lies 

 about two feet beneath a band of siliceous sandstone from 4 to 8 inches 

 in thickness, which carries casts of Pecten Immphreysii and other Miocene 



