MARYLAND GEOLOGICAL SURVEY 71 



Cliffs near Point of Eocks. \\'itli this breadth, it extends across south- 

 ern Maryland from Chesapeake Bay to the Potomac Eiver, and is devel- 

 oped along the latter stream from the hills north of Washincrton to 

 the mouth of the Wicomico. 



ISTot^vithstanding this great development, the Calvert formation is 

 seldom met with on the surface of the countiT hut must be sought in 

 the cliffs of the larger estuaries and in the walls of stream gorges. 

 As on the Eastern Shore so on the Western, the Calvert formation is 

 covered by younger formations. 



The distribution of the Calvert formation in this county is shown 

 on the geologic nuip wliicli accompanies this report. It is found 

 throughout the entire northern two-thirds of the region from Lyons 

 Creek to a point two miles below Governor Run on the Bay shore and 

 to the mouth of Ben Creek in the valley of the Patuxent River. Through- 

 out this region the Calvert formation is so extensively covered over by 

 the sands and gravels of the formations belonging to the Columbia 

 Group that it is nowhere found along the divides, but occurs in tlie 

 valley walls of every important stream. In the northwestern portion of 

 the coimty it lies unconiformably on the eroded surface of the Nanjemoy 

 formation. This contact occurs at an elevation of about 20 feet above 

 tide in the valley of Lyons Creek, but rapidly declines toward the 

 south until near the mouth of Hall Creek, the Nanjemoy dips below 

 the level of the Patuxent River, and the base of the Calvert formation 

 reaches tide. From this point southward to a line drawn from the 

 mouth of Ben Creek to the Calvert Clilfs, midway between Governor 

 Run and Flag Pond, the Calvert formation is found either in the sides 

 or the bottom of every creek valley, which is eroded to any considerable 

 depth. The headwaters of St. Leonard Creek and a few of its associates 

 on the southern margin of the Calvert area have not eroded quite deep 

 enough to reach it. By far the best exposure of the Calvert formation 

 is to be seen along the Calvert Cliffs from Chesapeake Beach south- 

 ward to two miles below Governor Run. Here there is an exposure of 

 the Calvert formation broken only for a short distance near Dares 

 Wharf, where some of the surficial deposits cover over and obscure it. 



