MARYLAND GEOLOGICAL SURVEY 69 



and the rivers flow from its surface as if they were flowing from a 

 country composed of unconsolidated deposits of clays, sands and 

 gravel horizontally bedded throughout. 



THE PIEDMONT PLATEAU REGION. 



The Topography of the Piedmont Plateau Region. — The Piedmont 

 Plateau is the name applied to a rolling and picturesque upland, 

 occupying the region between the Atlantic Coastal Plain on the east, 

 and the eastern margin of the Appalachian Mountain System on the 

 west, and extending from New York to the middle of Alabama. As 

 it passes through Maryland it varies in width from 85 miles in the 

 northeastern portion of the State to 37 miles in the southern portion. 

 In general it may be understood as that portion of the State of Mary- 

 land lying between the Baltimore and Ohio Railroad on the east, and 

 the Blue Ridge and Catoetin Mountain on the west. It will thus be 

 seen that the northern third of Cecil county lies within the Piedmont 

 Plateau region. 



Although the Baltimore and Ohio Railroad may be regarded 

 roughly as the boundary between the Piedmont Plateau and the 

 Atlantic Coastal Plain, yet the contact between them is by no means 

 as sharp as the definition would seem to indicate. On the one hand, 

 the deposits belonging to the Coastal Plain extend well up on the 

 surface of the Piedmont Plateau, in some instances as much as 5 

 miles north of the Baltimore and Ohio Railroad, and on the other 

 hand, the rocks of the Piedmont Plateau are exposed in the beds 

 of creeks well within the Coastal Plain and may reach as much as 

 one and a half to two and a half, or even three miles south of the 

 same railroad. The surface of the Piedmont Plateau is gently roll- 

 ing, except where it is crossed by the more important drainage lines, 

 such for instance as the Big Elk, Little Elk, Principio, Octoraro, 

 Conowingo creeks, and the Susquehanna river. Wherever these 

 streams cross the region they have cut deep and usually narrow 

 gorges imparting a rugged and picturesque beauty, to otherwise soft- 

 ened topography. Leaving the relative elevation aside for a moment, 

 there is between the general topography of the Piedmont region and 



