That's a slab of the Shawangunk Formation conglomerate, from eastern Pennsylvania. I collected it a couple of years ago when I drove up to go fossil hunting at the Whaleback, but it wasn't until last year that I slabbed and polished it. (The slab measures 10 cm wide by 27 cm in length.) Then a couple of months to get around to scanning it, and finally a few months more before posting it. Sheesh.

It's a lovely quartz-rich clast-supported conglomerate, a ridge former in the Valley & Ridge province of the Appalachians. Like the Massanutten Formation, it's Silurian in age, and thought to be part of the "molasse" sequence shed off the Taconian mountain belt, first raised during the late Ordovician. It is interpreted as a relatively-high-energy fluvial system deposit; sediments laid down by rivers as the mountains next door were weathered and eroded.

Labels: appalachians, pennsylvania, quartz, sediment, silurian, valley and ridge, weathering