MARYLAND GEOLOGICAL SURVEY i 1 



The Structure of the Piedmont Plateau Region. — The materials of 

 the Piedmont region consist of crystalline rocks of very great age. 

 These have been formed at various times, and nnder very different 

 conditions. The older rocks have been folded, rent asunder, and 

 intruded by younger rocks, which in their turn have been subjected 

 to the same processes until the region exhibits a most complicated 

 interlocking of metamorphic and eruptive rocks. 



Topographic History. 

 A careful study of these topographic features and of the deposits 

 which composed them, reveal some of the incidents which have given 

 rise to the present relief. An outline of the topographic history will 

 now be given, under the following seven stages, beginning with the 

 oldest: 



1. The Crystalline Kock Forming Stage. 



2. The Schooley Peneplain Stage. 



3. The Lafayette Stage. 



4. The Sunderland Stage. 



5. The Wicomico Stage. 



6. The Talbot Stage. 



7. The Eecent Stage. 



THE CRYSTALLINE ROCK FORMING STAGE. 



With the exception of remnants of Coastal Plain sediments, which 

 are scattered along the southern border of the Piedmont Plateau, 

 the rocks of the latter are either eruptive or metamorphic. Research 

 has shown that the Piedmont Plateau was part of an ancient uplift, 

 possibly a low mountain system, which was developed as a long, 

 narrow peninsula or island, extending from Canada to Alabama, and 

 separating the Atlantic Ocean on the east from a great Interior Sea 

 which covered the central part of K'orth America on the west. This 

 land mass ante-elated the Appalachian Mountain system, and the 

 materials which were stripped from its surface and carried out west- 

 ward into the Interior Sea, contributed in a large measure to the 

 building up of deposits which were afterward raised to form the 



