MARYLAND GEOLOGICAL SURVEY Ixxxi 



known, as the data from well records are too meagre to draw any con- 

 clusion regarding this question. Above, the Choptank formation lies 

 conformably beneath the St, Mary's formation. 



Subdivisions. 



Zone 16. — This zone varies in composition from yellowish sand to 

 bluish or greenish sandy clay. It is about 10 feet thick and may be 

 found exposed along the Calvert Cliffs from near Parker Creek south- 

 ward to a point a little north of Flag Pond, where it disappears be- 

 neath the beach. Where the Choptank first makes its appearance in 

 the Calvert Cliffs at Parker Creek this zone is absent, and Zone 17 of 

 the Choptank rests immediately upon Zone 15 of the Calvert. Zone 16 

 is for the most part unfossiliferous, although about 3 miles south of 

 Governor Eun a few fossils have been discovered in it, of which the 

 following are among the number : Ecpliora quadricostata, Venus 

 campechiensis var. cuneata, Dosinia acetabulum, PJiacoides contractus, etc. 



Zone 17. — The Choptank formation carries two well-defined fossil 

 zones. Of these, Zone 17 is the lower one. The material composing 

 this stratum is mostly yellow sand along the Calvert Cliffs. It is 

 almost entirely composed of fossils, the yellow saiid simply filling in the 

 spaces between the organic remains. The fauna of this zone is extremely 

 large, but the following will suffice to give an idea of some of the types : 

 Ecpliora quadricostata, Tun-itella plebia, Panopea americana, Corbula 

 idonea, C. cuneata. Metis biplicata, MacrocaUista marylandica, Ycnus 

 mercenaria, V. campechiensis var. cuneata, Dosinia acetabulum, Iso- 

 cardia fraterna, Cardium laqueatum, CrassatelUtes turgidulus, Astarte 

 thisphila, Pecten coccymelus, P. madisonius, Melina maxillata. Area 

 staminea, etc. This zone makes its appearance along the Calvert 

 Cliffs at Parker Creek, where it is about 6 feet in thickness, and is 

 continuously exposed until it dips beneath tide a little north of Flag 

 Pond. It may also be seen at various points on the Patuxent Eiver and 

 on the Eastern Shore. Zone 17 appears to thicken considerably south- 

 westward along the strike, for where best exposed on the Patuxent River, 

 as near the mouth of St. Leonards Creek, it is at least 18 feet thick, and 

 over 30 feet thick at Drum Cliff. This zone corresponds to " Zone e " of 



Harris.^ 



^ Loc. cit. 



