Natural History of District of Columbia — McAtee 75 



giniana) probably is not absent from one of them (of any 

 size), something which is not true of any other equally con- 

 spicuous plant. These bogs are restricted to Coastal Plain 

 formations, for it is only among those that the surficial 

 deposits give the proper basal conditions. Where a surface 

 layer, usually of coarse white gravel, or of gravel and sand 

 mixed, is underlaid by an impervious layer of clay ** and 

 flushed by a constant flow of spring water, there grows with- 

 out exception, and only there, some combination of the plants 

 which characterize what are here called Magnolia bogs. 



Such bogs exist at a number of points along Indian Creek 

 and its continuation the Eastern Branch, as at Ammendale, 

 Hollywood, Riverdale, Hyattsville, Bladensburg, Reform 

 School, Kenilworth and Deanewood. At the head of Brier 

 Ditch, a tributary, similar boggy spots exist at Lanham; 

 on the next tributary to the south are the Carter's Lane 

 and Lygodium bogs; and along Beaver Dam Branch, the 

 Magruder and Sarracenia bogs. On the other side of the 

 valley and flowing into Paint Branch are the four Powder- 

 mill bogs (others now drained once existed here) ; and tribu- 

 tary to Northwest Branch the Brookland, Terra Cotta and 

 Takoma bogs. Along Piney Branch and Rock Creek were 

 the two Brightwood bogs, Holmead Swamp, and Magnolia 

 Run Bog. The last four are all in the extreme edge of the 

 main body of Coastal Plain formations. In the bed of, and 

 across the creek from, Holmead and Magnolia Run bogs are 

 exposures of Piedmont Rocks. Along Four-mile Run Valley, 

 near Green Valley, and along the north side of Four-mile 

 Run Hill and Hunting Creek, are similar boggy spots. Bogs 

 of more or less the same nature exist at Laurel, Accotink ( ?), 

 Suitland, Silver Hill, Surattsville, Savage, Arundel and 

 Odenton. It may well be that a large number of such bogs 

 await discovery. 



It is the writer's purpose to describe in some detail the 

 Magnolia bogs with which he is best acquainted, namely, the 

 Powdermill bogs near Paint Branch (2 miles west of Belts- 



<3 By referring to the brief statement (p. 59) of the nature of Coastal 

 Plain and Piedmont deposits, it will be seen that only the former include 

 alternating clays and gravels. 



