MAKYLAXD GEOLOGICAL SUltVEV 111 



trated in two well-defined beds which seem to be distributed very 

 extensively through the areas of the deposit, though not represented 

 in Prince George's County. The fossils of this formation have 

 recently been fully described and illustrated in the two volumes on 

 the Miocene published by the Maryland Geological Survey. 



Strike, Dip, and Thickness. — The strike of the Choptank forma- 

 tion is in general from northeast to southwest ; but as a result of 

 erosion, particularly on the Western Shore of Chesapeake Bay, the 

 outcrop is very sinuous and the strike appears to change locally. 



The dip does not seem to be constant throughout the extent of the 

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

 the northern portion of the outcrop, down to Parker Creek, seems 

 to lie almost horizontal ; but farther south the formation at its base 

 dips southward at the rate of about 10 feet to the mile, so that toward 

 the south it occurs at 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 in this state to examine the dip of this 

 formation is along the Calvert Cliffs bordering Chesapeake Bay be- 

 tween Parker Creek and Point of Rocks. Here an almost unbroken 

 exposure of the Choptank may be seen dipping gradually toward the 

 southeast. 



The thickness of the Choptank formation is variable. In the well 

 section at Crisfield, mentioned in connection with the description of 

 the Calvert formation, the Choptank is more than 100 feet thick, so 

 that, like the Calvert, it thickens as it passes down the dip. 



Stratigraphic Relations. — The Choptank formation lies uncon- 

 formably upon the Calvert formation. The unconformity is in the 

 nature of an overlap, but is not easily discernible even where the 

 contact is visible. The best place to observe the unconformity is in 

 the portion of the Calvert Cliffs just below the mouth of Parker 

 Creek. Even here it can not be seen from the beach, but is visible 

 from a boat a short distance from the shore. This unconformity is 

 also proved by the fact that at the above-mentioned locality the fossil- 

 iferous bed which lies lowest in the Choptank formation rests upon 

 the Calvert, while at Mount Harmony, in Calvert County, and 



