The Billings, Carlsbad and Queenston Fromations are included together because they consist of basically dark shaley rock (Billings) which becomes interbedded with calcareous siltstone and silty limestone (Carlsbad), and then becomes an interbedded red to greenish gray siltstone and shale (Queenston). These fossilized rocks were formed in an anoxic marine environment (lack of oxygen), and are characterized by fossils made of pyrite (see Fossils). In addition to the fossils indicated in this composition, the Billings Formation contains gratolites; the Carlsbad Formation contains silty bioclastic limestone and shale with crinoids, brachiopods and bryozoans.

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