Ixxxiv GEOLOGICAL AXD PALEOJSTOLOGICAL RELATIONS 



Mail's formation have been found oiitcrdpping just west of St. Jerome 

 Creek and in the head-waters to the east at Smith Creek. In the 

 extreme southern portion of St. ]\Iary's count}^, however, tlie St. Mary's 

 formation seems to have been removed and loams and clays belonging to 

 the Columbia group deposited in its stead. 



Strik-r, Dip and TJtuliness. 



The strike of the St. Mary's formation, like that of the two pre- 

 ceding ones, is from northeast to southwest. On the Eastern Shore, 

 the occurrence and strike are approximately coincident; on the Western 

 Shore, however, due to the greater di^•er3ity in the topography, tlie 

 outcrop is extremely irregular and- departs very Avidely from the direc- 

 tion of strilce. The St. Mary's formation rests conformably on the 

 underlying Choptank and is overlain unconformably by younger mate- 

 rials. The dip averages about 10 feet to the mile toward the southeast. 



The thickness of the St. Mary's formation varies from nothing to 

 about 280 feet. In the liilltops south of Prince Frederick, where tlie 

 dip carries the formation up to an elevation of 100 feet or more, the 

 thickness thins down gradually to nothing; while in the well boring 

 at Crisfield it occupies a thickness of about 280 feet, although it is 

 possible that the upper portion of this may be Pliocene. 



Character of Materials. 

 The materials composing the St. Mary's formation consist of clay, 

 sand and sandy clay. As exposed in Maryland, it is typically a greenish- 

 blue sandy clay bearing large quantities of fossils and resembling very 

 closely the sandy clay of the Calvert formation described above. Locally, 

 the beds have been indurated by the deposition of iron and again in 

 other localities, notably on the south bank of the Patuxent river about 

 one-half mile west of Millstone Landing and again near Windmill 

 Point, clusters of radiating gypsum cry.sj:als are found. 



Stratigraphic Bdations. 

 The St. Mary's formation lies unconformably on the Choptank forma- 

 tion. It is overlain unconformably by clays, loams, sands and gravels 

 belonging to various members of the Columbia group. There are 



