MARYLAND GEOLOGICAL SURVEY 85 



Suh-Divisions. 



There are certain faunal clifTerences which separate it from the Chop- 

 tank formation. It has been subdivided into the following zones: 



Zone 21. — This zone lies at the base of the St. Mary's formation and 

 conformably on the Choptank formation. It consists of a drab clay 

 carrying sandy bands of about the same color and appears to be devoid 

 of fossils. It may best be seen along the cliffs south of Flag Pond, 

 where it has a thickness of about 15 feet. 



Zone 22. — Lying immediately above the last mentioned stratum is 

 another band of drab clay in which thin beds of fossils are developed. 

 These first made their appearance in the cliffs south of Flag Pond, and 

 although the continuity of this bed is interrupted along the Bay sliore 

 by talus slopes and overgrowth of woodland, still it is believed to bo 

 continuous with the fossil-bearing beds at the base of the cliff at 

 Cove Point. The following are soine of the more important fossils 

 found in this zone: Balanus concavus, Terehra inornata, Mangilia 

 parva, Nassa peralta, Columbella communis, Ecphora quadricostata, Tur- 

 ritella plebem, T. variabilis, Polyniccs heros, Corhula inequalis, Pecten 

 jeffersonim. Area idonea, etc. This stratum is about 14 feet in thick- 

 ness. It corresponds to "Zone g" of Harris." 



Zone 23. — This zone is composed of drab clay and sand. It has suf- 

 fered considerably from erosion, but along the Calvert cliffs it carries 

 some fossils of which Turriiella pleheia is the most important. It shows 

 a thickness of 30 feet, but is unconformably overlain by the Pleistocene 

 sands and gravels. 



Zone 24. — A break in the strati gi-aphic continuity of the St. Mary's 

 formation occurs south of Drum Point and the exact relation of this 

 zone to those preceding is not definitely known. It is believed, how- 

 ever, to lie very close to Zone 23. At Chancellor Point on the St. Mary's 

 Elver, where it has been studied, 15 feet of bluish sandy clay are ex- 

 posed, overlain unconformably by Pleistocene loams. At this place a 

 large number of fossils are present, of which the following may be 

 mentioned: Acetco7i ovoides, Retusa marylandica, Terehra curvilirata, 



° Loc. cit. 



