96 THE GEOLOGY OF CALVERT COUNTY 



on one side and to Chesapeake Bay on the other. The most pronounced 

 slope is toward the former as much of the Sunderland formation has 

 been eroded from the latter. 



The thickness of the Sunderland formation is extremely variable. 

 About a mile south of Little Cove Point, near the mouth of the Patuxent 

 Eiver, a thickness of 85 feet has been measured, which is the greatest 

 anywhere visible throughout the county. From this it thins down and 

 disappears. Its average thickness for the region is very close to 35 feet. 



CJiaracter of Materials. 



The materials which compose the Sunderland formation consist of 

 clay, loam, peat, sand, gravel, and ice-borne boulders. These, as a rule, 

 do not lie in well-defined beds, but grade into each other both vertically 

 and horizontally. The coarser materials, with the exception of ice-borne 

 boulders, are usually found with a cross-bedded structure, while the 

 clays and finer materials are either developed in lenses or are horizontally 

 stratified. The ice-borne blocks are scattered through the formation 

 and may occur in the gravel beneath or in the loam above. There is 

 distinguishable throughout the formation a tendency for the coarser 

 materials to occupy the lower portions and the finer the upper portions 

 of the formation, but the transition from one to the other is not marked 

 by an abrupt change. The coarser materials are frequently found above 

 in the loam and the finer materials below in the gravel. Many of these 

 materials are in an advanced stage of decay. A fossil bed bearing car- 

 bonaceous matter containing recognizable plant remains occurs at Point 

 of Rocks. 



Stratigraphic Relations. 



The Sunderland formation is built as a terrace lying unconformably 

 and somewhat irregularly on the older deposits of Eocene and Miocene 

 age. This terrace was laid down about the margin of the Lafayette 

 formation although this relation, so well shown in adjacent regions, is 

 not represented in this county. At Charlotte Hall, in St. Mary's County, 

 and at Marriott Hill, in Anne Arundel County, the surface of the Lafay- 



