MARYLAND GEOLOGICAL SURVEY 75 



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 imfossiliferous, although about 3 miles south of 

 Governor Run a few fossils have been discovered in it, of wliich the 

 following are among the number: Ecpliora quadricostata, Venus cam- 

 pechiensis var. cuneata, Dosinia acetabulum, Phacoides 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 sand simply filling in 

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

 extremely large, but the following will suflBee to give an idea of some 

 of the types : 



Ecpliora quadricostata, Turritella pleheia, Panopea amencana, 

 Corbula idonea, C. cuneata. Metis biplicata, Macrocallista marylandica, 

 Venus mercenaria, V. campechiensis var. cuneata, Dosinia acetabulum, 

 Isocardia fratcrna, Cardium laqueatum, Crassatellites turgidulus, Asiarte 

 thispliila, 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. It appears to thicken 

 considerably southwestward along the strike, for where best exposed 

 on the Patuxent Eiver it is at least 18 feet thick near the mouth of 

 St. Leonard Creek and over 30 feet thick at Drum Cliff, in St. Mary's 

 County. This zone corresponds to " Zone e " of Harris.' 



Zone 18. — This zone is for the most part unfossiliferous, although 

 in places it carries some imperfect fossils and fossil casts. The mate- 

 rial of which it is composed is for the most part yellowish sand above 

 but grades down into bluish clay below and at times the entire stratum 

 is composed of bluish clay. In thickness it varies from IS to 22 



'Tertiary Geology of Calvert Cliffs, Maryland. Amer. Jour. Sci., vol. xlv, 

 1893, pp. 21-31. 



