Ixxviii GEOLOGICAL AXD PALEOXTOLOGICAL RELATIONS 



THE CPIOPTANK FORMATION. 



The Choptank river has suggested the name for this formation be- 

 cause of its great development on the northern bank of that estuary a 

 short distance below Dover Bridge. In this locality the Choptank 

 formation is very fossiliferous and may be seen at the base of a low 

 cliff which borders the stream for some distance. 



Areal Distribution. 



The Choptank formation, which constitutes the second member of 

 the Chesapeake Group in Maryland and lies immediately above the 

 Calvert formation, is found in Caroline, Talbot and Dorchester counties 

 on the Eastern Shore, and Anne Arundel, Calvert, Prince George's, 

 Charles and St. Mary's counties on the Western Shore. On the Eastern 

 Shore the Choptank formation is so completely buried beneath the 

 surface cover of Columbia sand and loam that its exact areal distribu- 

 tion is not definitely known. Its presence, however, has been detected 

 in the area indicated in numerous marl pits and well borings, although 

 the location of its northern and southern boundaries is largely a matter 

 of conjecture. The northern boundary appears to enter Caroline county 

 a little northeast of Greensboro and from there crosses in a south- 

 western direction to the mouth of the Choptank river. The southern 

 boundary follows a parallel course, cutting across southern Caroline 

 county, crossing the Choptank river not far from Cambridge and reach- 

 ing the Bay in about the middle of Taylor Island. 



In Calvert county, on the Western Shore, the Choptank formation is 

 not so much obscured by the Columbia deposits as it is in the counties 

 of the Eastern Shore. It may be found in a long line of outcrops ex- 

 tending from the hilltops just west of Herring Bay to a place on the 

 Calvert Cliffs a little distance north of Cove Point. It is also found 

 at intervals along the Patuxent river, but west of this estuary it is 

 almost as much obscured by younger deposits as on the Eastern Shore. 

 The boundaries of the Choptank formation in Calvei't county, although 

 in part conjectural, are better known than in any other portion of 

 southern Maryland, but the limitations set to its distribution in certain 

 parts of Prince George's and Charles counties have been determined 

 more by calculation than from observation. They are believed, how- 



