70 THE PHYSIOGRAPHY OF PKINCE GEOKGe's COUNTY 



striking contrast to the swift streams of the other two provinces 

 which flow in steep rock-walled gorges; while the superimposed, 

 meandering streams of the Piedmont Plateau are markedly unlike 

 the Appalachian streams which flow in structural valleys. But 

 probably the greatest distinction between the three provinces is due 

 to the character of the rocks. The unconsolidated sediments of the 

 Coastal Plain, dipping gently toward the ocean, are sharply sepa- 

 rated from the contorted metamorphosed igneous intruded strata of 

 the Piedmont Plateau, while these in turn can be readily differenti- 

 ated from the unmetamorphosed Appalachian Ptegion limestones and 

 sandstones which have been thrown into broad, open folds, forming 

 longitudinal ridges and valleys with a northeast-southwest trend. 



Prince George's County lies almost entirely within the eastern 

 province and is known as a Coastal Plain county, although its ex- 

 treme western portion forms a part of the Piedmont Plateau. 



TOPOGKAPHTC DeSCKIPTION, 



As previously stated, Prince George's County contains portions of 

 two great physiographic provinces which have characteristic topo- 

 graphic features. The topography of the Piedmont Plateau in this 

 county, however, is not characteristic of the general topography of 

 the province for the reason that it has been greatly modified by the 

 Coastal Plain deposits overlying it. It is represented only in the 

 uplands west and northwest of Washington and in small areas along 

 the western border of the county between Washington and Laurel. 

 Within the area under discussion the northwest portion of the Dis- 

 trict of Columbia shows the best examples of Piedmont Plateau 

 topography. Here occur many hills, irregular in outline with rounded 

 flat-topped summits separated from each other by steep, precipitous 

 valleys. Those hills without coverings of Coastal Plain sediments 

 are seldom flat-topped but instead slope gradually in all directions 

 for a short distance from the highest point, and then very rapidly to 

 the streams occupying the narrow gorge-like valleys. 



In the Coastal Plain portion of the county the flat-topped stream 

 divides separated by broad open valleys afFord a striking contrast to 

 the topography of the Piedmont Plateau. The broad tidal estuaries 



