Bryn Mawr Formation
Reddish-brown to yellowish-brown silty quartz sand to sandy silt that interfingers with medium to coarse clayey sand with gravel. Sand fraction, where a sandy silt, is fine- to very fine-grained and angular to subangular. Iron-cemented zones are common. Gravel fraction is primarily quartz. Sands are quartzose with minor amounts of weathered feldspar. Opaque heavy minerals form up to 3 percent of the sand fraction. Unit ranges up to 70 ft thick but generally less than 30 ft thick and commonly less than 10 ft thick. Surface forms a distinctive terrace that has elevations between 350 ft and 425 ft, and it overlies saprolite of the Piedmont rocks. No macrofossils have been recovered. Fossil pollen from the York Pit in Cecil County, Maryland (Pazzaglia, 1993; unpublished DGS data) indicate a Miocene age. Owens (1999) considered the unit late Oligocene in Pennsylvania.