The Pottsville Group is a Pennsylvanian-aged cyclothemic succession containing nonmarine shales, marine shales, siltstones, sandstones, coals, marine limestones, and chert ("flint"). The lower Pottsville dates to the late Early Pennsylvanian. The upper part dates to the early Middle Pennsylvanian. The Lower-Middle Pennsylvanian boundary is apparently somewhere near the Boggs Limestone horizon (?).

The ledge-like unit exposed just above the leaf-covered talus pile in the above photo is the Boggs Member, a relatively thin stratigraphic interval in the Pottsville Group. It typically consists of marine fossiliferous limestones, dominated by brachiopods and crinoid ossicles. Significant lateral and vertical lithologic variation is present - the Boggs interval ranges from being a fossiliferous limestone to an intraclastic limestone to a chert to a dolostone. In places, it has a relatively high component of disseminated pyrite. In other places, it is relatively rich in black manganese oxide(s).

Minerals observed in the Boggs Limestone interval: calcite, dolomite, glauconite, goethite, gypsum, limonite, pyrite, sphalerite, turgite, vivianite, wad.

At this site, the Boggs is principally a ferruginous fossiliferous chert/flint. The fossils and fossil fragments show up as light-colored specks in the rock (see: <a href="https://www.flickr.com/photos/jsjgeology/31215514761">www.flickr.com/photos/jsjgeology/31215514761</a>).

This is the first locality where I ever observed the Boggs Member - it's a scrappy exposure for Boggs, although the site is excellent for seeing supra-Boggs stratigraphy. Blocks of ferruginous flint derived from the Boggs is scattered about as talus - this is one of two spots that have Boggs outcrop.

Stratigraphy: Lower Mercer Limestone & Boggs Member, Pottsville Group, lower Atokan Stage, lower Middle Pennsylvanian