86 THE GEOLOGY OF PRINCE GEOKGE S COUNTY 



formation "were readily separable into distinct formations on the basis 

 of unconformities and fossil content. 



Ai-eal Distribution. — The area of outcrop of the Patuxent forma- 

 tion extends from the mouth of Piscataway Creek up the west shore 

 of the Potomac Piver to and beyond Anacostia River which, with its 

 tributary, Indian Creek, constitutes for the most part the eastern 

 boundary of the formation. It underlies the greater portion of the 

 City of Washington and extends as almost continuous outcropping 

 beds to Laurel. 



Character of Materials. — The materials composing the Patuxent 

 formation are extremely variable, although prevailingly arenaceous. 

 Buff and light-colored sands, both fine and coarse, predominate, while 

 beds and lenses of clays and gravels occur less commonly. The sandy 

 strata, which usually contain considerable amounts of kaolinized 

 feldspar and are therefore an arkose, were called by Rogers "felds- 

 pathic sandstone." The sands are in many places cross-bedded, and 

 M'ith the gravels are here and there indurated by oxide of iron to form 

 ferruginous sandstones. The sands contain small and large lenses of 

 clay, which are commonly light in color, though locally they are 

 highly colored by iron compounds. 



The following section exposed in the northwestern part of Wash- 

 ington, is characteristic of the formation : 



Section in nortliioe stern part of Washington. D. C. 



Sunderland: Feet. 



Red loam 2 



Stratified gravels, sands, and clays 23 



Patuxent : 



Coarse white arkosic pebbly sand, slightly lignitic; small 

 pellets of white clay, and a lens of light greenish- 

 drao sandy clay 5 feet in thickness. The strata show 

 both horizontal and cross bedding. Amount exposed. . 15 



40 



Paleontologic Character. — The organic remains of the Patuxent 

 formation are neither plentiful nor varied. I^o animal remains have- 

 thus far been found in deposits of this age within Prince George's 

 County, but a teleost fish has been reported from beds of apparently 

 the same age on James River in Virginia. Plant remains are equally 

 rare and consist chieflv of the liffnitized and silicified trunks of 



