MARYLAND GEOLOGICAL SURVEY 81 



Stratigrapliic lielations. 



The Choptank formation lies iinconformably on the Calvert forma- 

 tion. This imconformity is in the nature of an over-lap but is not 

 easily discernible even where the contact is visible. The best place to 

 observe it is in that portion of the Calvert Cliffs just below the mouth 

 of Parker Creek. Even here, the unconformity cannot be seen while 

 standing on the beach but may be observed from a boat a short distance 

 from the shore. The unconformity of the Choptank on the Calvert 

 formation is also jiroved i'lom the fact that at the above-mentioned 

 locality the fossil bed which lies lowest in the Choptank formation 

 rests on the Calvert, while at Mt. Harmony and northward the upper 

 fossil bed of the Choptank rests on the Calvert formation. There are 

 also certain differences between the fauna of the Calvert and that of 

 the Choptank, How far this unconformity continues down the dip 

 after the beds disappear from view is not known, as the data from well 

 records are too meager to draw any conclusion regarding this question. 

 Above, the Choptank formation lies conformably beneath the St. Mary's 

 formation. 



Sub-Divisions. 



The Choptank formation has been subdivided into five zones which 

 may be characterized as follows : 



Zone IG.^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. Whore 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 IG 

 is for tlie 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: EcpJiora quadricostaia, Venus cam- 

 pechiensis var. cuneata, Dosinia acetabulum, Phacoidcs contractus, etc. 



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



