100 THE GEOLOGY OF CALVERT COUNTY 



Many streams have forced their headwaters back into the body of 

 the Wicomico formation so that it no longer is as continuous as when 

 first deposited, but has developed a sinuous outline and is broken into a 

 number of isolated areas. 



Structure and Thickness. 



The base of the Wicomico formation throughout the county rests at 

 an elevation of about 40 or 45 feet and has suffered apparently little or 

 no deformation since it was deposited. There is, however, a gentle slope 

 from the inner margin to its outer edge where it approaches the sur- 

 rounding waters. This is not to be attributed to a tilting of the forma- 

 tion, but is due to the original slope which the formation had when it 

 was deposited. 



The thickness of the Wicomico formation is extremely variable. Near 

 Dares wharf a thickness of 38 feet has been measured. In other places, 

 however, the formation has been found to thin down and disappear. 

 Its average thickness for the county is about 20 feet. 



Character of Materials. 



The materials which compose the Wicomico formation consist of 

 clay, loam, 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 hori- 

 zontally stratified. The ice-borne blocks are scattered throughout the 

 formation and may occur in the gravel beneath or in the loam above. 

 There is distinguishable throughout a tendency for the coarser materials 

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

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

 marked by an abrupt change. The coarser materials are frequently 

 found above in the loam and finer materials below in the gravel, and are 

 frequently much decaj^ed. 



