The pre-Dundee rocks outcropping in the Sibley quarry near Trenton, Michigan, contain abundant and well-preserved stromatoporoids comprising 2 genera and 4 species: Anostylostroma sibleyense n. sp., A. ponderosum (Nicholson), and Syringostroma densum Nicholson and S.sherzeri are known from the Columbus Limestone of Northern Ohio; this suggests that the pre-Dundee rocks at Sibley are perhaps equivalent to the Columbus rather than the Anderdon Limestone as assumed by previous authors. S. sherzeri is present in the Amherstburg Dolomite and Formosa reef limestone and perhaps in the Upper Abitibi River and Jeffersonville limestones.

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