Ixxiv GEOLOGICAL AND PALEONTOLOGICAL RELATIONS 



ably on the Eocene deposits is a bed of brownish sand carrying Phacoides 

 contractus. This stratum varies somewhat in thickness from place to 

 place, but does not depart widely from six feet on the average. 



Zone 2. — Lying immediately above Zone 1 is a thin stratum of white 

 sand of about one foot in thickness which is locally indurated to sand- 

 stone. It contains a large number of fossils, of which the following 

 are the most important: Ecpliora tricostata, Panopea ivhitfieldi, P. 

 americana, Corhula elevata, Phacoides contractus, Venericardia granu- 

 lata, Astarte cuneifonnis, A. thomasi, Thracia conradi, Pecten madi- 

 sonius, P. humphreysii, Chione latilirata, Cytherea staminea. 



Zone 3. — This stratum when freshly exposed consists of a greenish 

 colored diatomaceous earth which, on weathering, bleaches to a white 

 or buff-colored deposit breaking with a columnar parting and presenting 

 perpendicular surfaces. It is very rich in diatomaceous matter, the me- 

 chanical analysis of specimens yielding more than 50 per cent of diatoms. 

 The thickness of this bed varies from place to place, but where it is pen- 

 etrated at Chesapeake Beach by an artesian well it has a thickness of 

 about 55 feet. At Fairhaven, where it is well exposed, it carries large 

 numbers of Phacoides contractus. This zone is best exposed at Popes 

 Creek, Lyons Creek, Fairhaven, and in stream gullies lying along the 

 northern margin of the Miocene beds. 



Plum Point Marls. — The Plum Point marls occupy the remainder 

 of the Calvert formation above the Fairhaven diatomaceous earth. 

 Plum Point in Calvert county where the beds are typically developed, 

 has suggested the name for this member. These marls consist of a 

 series of sandy-clays and marls in which are imbedded large numbers 

 of organic remains including diatoms. The color of the material is 

 bluish-green to grayish-brown and buff. Fossil remains although 

 abundant through the entire member are particularly numerous in two 

 prominent beds from 30 to 35 feet apart. These beds vary in thick- 

 ness from 4^ to 13 feet. They may be easily traced along the Calvert 

 Cliffs from Chesapeake Beach to a point 2 miles below Governor Run. 

 At Chesapeake Beach they lie high up in the cliffs and pass gradually 

 downward beneath the surface of the water as the formation is followed 

 southward. Along the Patuxent river the Plum Point marls are 

 not exposed so extensively as. in the Calvert Cliffs but they are visible 



