78 THE PHYSIOGEAPIIY OF PRIXCE GEOKGE S COU^SfTY 



Tlie Potomac River receives many tributaries which drain por- 

 tions of the county. Anacostia River, Oxon Run, Broad and 

 Piscataway creeks, all of which are estuaries in their lower portions, 

 are the most important. The heads of their estuaries are all being 

 gradually filled by the materials brought down by their headwaters 

 and by the accumulation of vegetable debris of marsh grasses which 

 thrive in the shallow waters. Since the settlement of the region all 

 of these streams have shown an appreciable amount of shoaling and 

 navigation is now restricted to a very short distance from their 

 junctions with the Potomac River. At present Anacostia River is 

 not navigable above the bridge between the ]S"avy Yard and Ana- 

 costia, while Piscataway Creek is navigable as far up as Farmington 

 Landing and that only at high tide. 



Tlie Patuxent Rive)'. — The Patuxent River forms the boundary 

 of Prince George's County on the east and northeast sides. In most 

 respects this stream is very much like the Potomac. Like it, it 

 descends from the Piedmont Plateau as a rather swift-flowing stream 

 in a rocky channel and quickly changes its character to a sluggish 

 stream with banks of mud so soon as it enters the Coastal Plain. 

 This change takes place at Laurel, where the crystalline rocks of 

 the Piedmont Plateau disappear beneath the covering of uncon- 

 solidated sediments. In the Patuxent River tide water does not 

 extend up to the inner margin of the Coastal Plain as in the Potomac. 



The channel of that portion of Patuxent River bordering Prince 

 George's County is about 16 feet deep in the southern portion and 

 shallows gradually to Leon, which is the head of steamboat naviga- 

 tion. The river is bordered by marshy areas in many places through 

 which the stream meanders in broad, open loops. 



Of the tributaries of the Patuxent River the Western Branch is 

 the only one of any considerable importance. This stream drains a 

 large area in the northern part of the County. Mataponi, Rock, 

 Black Swamp, and Swanson creeks drain most of the southeastern 

 portion of the County. 



