80 THE GEOLOGY OF CALVERT COU^ITY 



as pointed out above, the outcrop is very sinuous and the strike appears 

 to change locally. 



The dip does not appear to be constant throughout the entire extent 

 of the formation. In Calvert County, where the Choptank is best 

 exposed, the northern portion of the formation down to Parkers Creek 

 seems to lie almost horizontal; but south of this point the base of the 

 formation dips away at about 10 feet to the mile. Because of this 

 structure, the Choptank formation occupies hilltops in the northern por- 

 tion of its area and gradually occupies lower and lower levels, until in 

 the southern portion of its area it is found in river bottoms and finally 

 disappears beneath tide. The best place to examine the dip of the 

 Choptank formation is along the Calvert Cliffs between Parker Creek 

 and Point of Eocks. Here an almost unbroken exposure may be seen 

 dipping gradually toward the southeast. 



The thickness is variable. In the Nomini Cliffs, Virginia, it is 

 present as a 50-foot bed between the Calvert formation below and the 

 St. Mary's formation above. This is the thickest exposure which is 

 open to direct observation. In the well section at Crisfield, mentioned 

 above in connection with the Calvert formation, the Choptank forma- 

 tion attains a tliickness of about 175 feet. It will thus be seen that 

 like the Calvert, it thickens as it passes down the dip. The average 

 thickness in Calvert County appears to be about 100 feet. 



Character of Materials. 



The materials composing the Choptank formation are somewhat vari- 

 able. They consist of fine yellow quartz-sand, bluish-green sandy- 

 cla}'-, slate-colored clay and, at times, ledges of indurated rock. In 

 addition to these materials, there are abundant fossil remains dissemi- 

 nated throughout the formation. The sandy phase is well shown in 

 the Calvert Cliffs from Parker Creek southward to Point of Rocks. 

 The sandy-clay and clayey members may be seen in the same cliffs near 

 Point of Eocks and southward. The indurated rock is well shown in 

 Drum Cliff on the Patuxent and at Point of Rocks, and the fossil re- 

 mains are seen typically developed at Drum Cliff and at Governor Eun. 



