MARYLAND GEOLOGICAL SURVEY 85 



(Fig. 4). They all dip oently toward the surrounding waters and to- 

 gether are widely distributed over the surface of the county and obscure 

 in a great measure the older deposits which lie beneath them. 



THE SUNDERLAND FORMATION. 



The Sunderland formation has been named from its typical develop- 

 ment near the hamlet of Sunderland in Calvert County. It consists of 

 a wave-built terrace, which was formed by the waters of the Atlantic 

 Ocean or its estuaries when the country stood at a lower level than to-day. 

 It is distributed over the entire county occupying the divides between 

 the headwaters of the principal streams. Since the time of deposition, 

 the Sunderland formation has suffered extensively from erosion. Water- 

 ways have opened up their valleys through it and have transformed a 

 once continuous mantle of loam and gravel into a series of isolated 

 patches with sinuous outlines occupying the higher portions of the 

 county, and its once level surface has now been changed by the same 

 processes into a gently rolling upland. 



Areal Distribution. 



The Sunderland formation is the most widely developed of the 

 Pleistocene deposits in St. Mary's County. With the exception of the 

 isolated outliers of Lafayette in the vicinity of Charlotte Hall, it occu- 

 pies the highest divides from the northern margin of the country, near 

 Indian, southward to Eidge, near Point Lookout. On either side in both 

 the valleys of the Patuxent and Potomac rivers, as well as in the gorges 

 of the streams which are tributary to these estuaries, the Sunderland 

 formation is surrounded by terraces of the 3^ounger formations of the 

 Columbia Group, which lie beneath it. These terraces are more ex- 

 tensively developed in the Potomac than in the Patuxent Valley. 



Many streams have forced their headwaters back into the body of the 

 Sunderland formation, so that it is no longer as continuous as when 

 first deposited, but has developed a sinuous outline. 



