It preserves fossils dating back to the Katian stage of the Ordovician period, or Shermanian to Chatfieldian in the regional stratigraphy.

Both the Bobcaygeon and Verulam Formations are composed of bioclastic wackestones, grainstones, and packstones interbedded with calcareous shales and siltstones.

Several hardgrounds have been documented in detail from the upper Bobcaygeon and lower Verulam.

Both formations form the Brechin Lagerstätte, a Lagerstätte of excellent preservation of numerous exceptionally preserved crinoid specimens with arms, stems, and attachment structures intact.

[2][3][4] Also ostracods, trilobites, bivalves, gastropods, cephalopods and other fossils were found in the formation.