126 THE GEOLOGY OF PRINCE GEORGE S COUNTY 



northwest of Upper Marlboro at the road crossing of Cabin Branch 

 near the Western Branch of the Patuxent River. It is now pre- 

 served in the musenm of Georgetown University. I^^ear Cornfield 

 Harbor, at the month of Potomac River, the formation has yielded 

 a great number of molhiscan shells representing a varied fauna of 

 marine and brackish-water origin. Practically all the plants and 

 animals are forms which still exist in this or other regions. 



Thickness. — The thickness of the Talbot formation is extremely 

 variable, ranging from a few feet to 40 feet or more. The uneven- 

 ness of the surface upon which it was deposited has in part caused 

 this variability. The proximity of certain regions to the mouths of 

 streams during the Talbot submergence also accounts for the in- 

 creased thickness of the formation in such areas. 



Stratigraphic Relations. — The Talbot rests unconformably, in 

 diiferent portions of the region, upon various older formations belong- 

 ing to the Cretaceous or Tertiary systems. It may in places rest 

 upon deposits of Lafayette, Sunderland, or Wicomico age, although 

 no positive evidence has yet been found to indicate such relations to 

 the older Pleistocene formations. The deposits occupy a nearly 

 horizontal position, having only a slight slope Toward Chesapeake 

 Bay and its estuaries. 



The Recent Deposits. 



In addition to the four terraces already discussed, a fifth is now 

 being formed by the waters of the rivers and the Avaves of the estu- 

 aries. This terrace is everywhere present along the water's edge, 

 extending from a few feet above tide to a few feet below. It is the 

 youngest and topographically the lowest of the series. jSTormally it 

 lies beneath and wraps about the margin of the Talbot terrace, from 

 which it is separated by a low scarp that as a rule does not exceed 

 15 to 20 feet in height. Where the Talbot formation is absent, the 

 Recent terrace may be found at the base of either of the other three 

 terraces. In such places, however, the scarp which separates them 

 is higher in proportion as the upper terrace is older. Peat, clay, 



