MARYLAND GEOLOGICAL SURVEY 83 



and is continuously exposed from Parker Creek southward to near Cove 

 Point, where the stratum dips beneath the beach. The following is 

 a partial list of fossils found in this zone: Balanus concavus, Carhiila 

 idonea, MacrocaUisia marylandica , Dosinia acetabulum, Cardium laquea- 

 tum, Phac&ides anodonia, Crassatellites marytandicus, Astarte thisphila, 

 Ostrea caroUnensis, Pecten madisonius. Area staminca, etc. This zone 

 corresponds to " Zone f " of Harris.* 



Zone 20. — This zone lies at the top of the Choptaiik formation. It 

 consists of greenish sand wliich is frequently oxidized to a red color, 

 and at times it carries bands of clay. It seems to be devoid of fossils 

 and is 15 feet thick, although it has frequently suffered by erosion. It 

 may be best seen near Flag Pond, where it is overlaid by the St. Mary's, 

 formation. 



THE ST. MARY's FORMATION, 



The name of this formation has been suggested by St. Clary's County 

 on account of its great development within that region. The formation 

 is found exposed in numerous places along the St. Mary's Eiver in the 

 vicinity of St. Mary's City. In Calvert County it is best seen along 

 the Calvert Cliffs from Point of Rocks southward to Drum Point. 



Areal Distribution. 



The St. Mary's formation, like the Calvert and the Choptank forma- 

 tions, crosses the state from northeast to southwest. On the Eastern 

 Shore, it is present, if at all, in Caroline, Talbot, Wicomico and Dor- 

 chester counties. 



On the Western Shore the St. ^Mary's formation is found developed 

 in southeastern Calvert and St. Mary's counties. In this region 

 it is very much obscured by a mantle of younger material lie- 

 longing to the Columbia Group and is, therefore, seldom seen on the 

 surface. Good exposures, however, are found along the Bay shore and 

 the Patuxent Eiver and its tributaries. The most extensive exposure 

 is found in Calvert County along the Bay shore from Point of Eocks 



' Loc. cit. 



