72 THE PHYSIOGRAPHY OF CECIL COUNTY 



Appalachian Mountains. The extent of this ancient land mass can- 

 not be accurately determined, but it seems certain that only a portion 

 of it is represented by the Piedmont Plateau, and that another large 

 part has disappeared and is now buried beneath Coastal Plain sedi- 

 ments or submerged beneath the waters of the Atlantic Ocean. 



A portion of the Piedmont rocks which are now crystalline, were 

 not always so, but were in the form of sediments deposited by an 

 ancient sea. On being folded up into a mountain system, they were 

 not only transformed from clastic to metamorphic rocks, but were 

 also injected with a quantity of eruptive rocks, introduced from lower 

 regions. These rocks, which were first situated deep within the 

 earth's crust, have been brought to the surface by the erosion of the 

 cover which formerly overlaid them, and now lie exposed in the 

 Piedmont hills. 



THE SCHOOLEY PEKEPLATN" STAGE. 



At the close of the Paleozoic period, the sediments which had been 

 accumulated in the Interior Sea to the west of the Piedmont Plateau, 

 were raised into the Appalachian Mountains. It is not known that 

 the Piedmont Plateau shared in this movement, but it is certain that it 

 suffered greatly during the erosion interval which followed. This 

 period of erosion, which took place in Mesozoic time, was of great 

 duration and extent. When it began, the Appalachian Mountains 

 were probably as high, if not higher, than they are today; when it 

 came to a close, the mountains had almost entirely vanished, and in 

 their place there was a low and nearly featureless plain which ex- 

 tended out across the Piedmont Plateau to the Atlantic Ocean. This 

 peneplain, which was almost co-extensive with the Appalachian uplift, 

 is known in Maryland and the neighboring regions as the Schooley 

 peneplain. Before this erosion period came to a close, however, the 

 eastern margin of the Piedmont Plateau seems to have been depressed 

 below tide-level, and buried under a load of Cretaceous sediments; 

 thus while erosion was completing the plaination of the interior por- 

 tion of the Schooley peneplain, deposition was taking place along its 

 eastern border. The deposition of these sediments was not contin- 



