The Guelph Formation is a geologic formation in New York and in Ontario, Canada. It preserves fossils dating back to the Silurian period.Guelph, USGS, National Geologic Map Database, Geolex — Unit Summary
Fossils Fossils within the formation include: Pentamerus occidentalis (Hall) Megalomus canadensis (Hall) Murchisonia bivittata (Hall) M. macrospira (Hall) M. boydii (Hall) M. logani M. longispira M. uvittata M. turritiformis M. tullia Subulites ventricosus (Hall) Pleurotomaria solaroides (Hall) P. elora (Billings) P. galtensis (Billings) P. mora Cyclonema sulcata (Hall) C. galtensis C. thysbe C. psyche C. depressa Holopea guelphensis (Billings) Bellerophon angustata (Hall) Favosites gothlandica F. polymorpha Halysites catenulatus Columnaria galtensis Obolus sp. Orikoceras sp. Orthoceras darwini Cyrtoceras arcticameratum C. Jonesi Phragmoceras hector Calymene blumenbachii Diphyphyllum irregulare Amplexus laxatus Rhynchonella sp. Athyris sp.
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