MARYLAND GEOLOGICAL SURVEY Ixxix 



ever, to be approximately correct and are fixed as accurately as our 

 present knowledge warrants. 



The streams of the Western Shore have cut deeper and more ramifying 

 channels than those of the Eastern Shore and the contact of the Chop- 

 tank with the Calvert formation appears consequently very irregular. 

 The northern border of the Choptank formation extends in a ]Sr. E.- 

 S. W. direction from the hills west of Herring Bay to the flat country 

 at the head-waters of AYicomico river. The southern border of the 

 Choptank formation is also a diagonal line running approximately par- 

 allel with the northern border and extending from near Cove Point on 

 Chesapeake Bay to the mouth of Flood Creek on the Potomac river. 

 This last locality is only approximately fixed as the ]\Iiocene beds in 

 this region are obsciired by younger deposits. The point where the 

 Choptank formation dips below the tide cannot, however, be very far from 

 the locality indicated. 



Strike^ Dip and Tliichncss. 



The strike of the Choptank formation is in general from northeast 

 to southwest; but due to erosion, particularly on the Western Shore, 

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

 to change locally. On the Eastern Shore, as the country is extremely 

 fiat, the rivers have not opened up extensive drainage lines and the out- 

 crop is therefore approximately parallel to the strike. 



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 KJ feet to the mile. Due to this struc- 

 ture, 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 of the Chop- 

 tank may be seen dipping gradually toward the southeast. 



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



