A succession of Devonian strata, ranging in age from Pragian? to Famennian and possibly postFamennian, occurs in southwestern Ontario. The Lower Devonian sequence comprises the sandstone of the Oriskany Formation (Pragian?), cherty dolomitic limestone of the Bois
Blanc Formation (robust us Zone , and possibly equivalent to the serotinus Zone; Emsian), the bioclastic limestone of the Amherstburg Formation (possibly serotinus to patulus Zones; Emsian?) and the lithologically variable Lucas Formation. The latter two units form the Detroit River Group. The sandy
limestone facies ("Columbus limestone"), developed within the Anderdon Member of the Lucas Formation, contains conodonts of the patulus Zone (undivided). Pending the final decision, the Lower-Middle Devonian boundary lies very close to the patulus Zone, and therefore to the Anderdon Member. In the
Niagara Peninsula, New York nomenclature is applicable, and parts of the Onondaga Formation are recognized (in ascending order): Edgecliff, Clarence, and Moorehouse Members. The true relationship of the Onondaga and the Detroit River is still not entirely known.
At the base of the Middle Devonian sequence is the fossiliferous, micritic limestone of the Dundee Formation which lies disconformably on the Detroit River strata. Dundee conodonts are assignable to the costatus costatus, australis and kockelianus Zones, of Eifelian age. The overlying Hamilton
Group, studied only in outcrop sections, includes the upper part of the Arkona Formation (shale), and the Hungry Hollow (shale and limestone), Widder (shale), and Jpperwash (jimestone) Formations. The conodonts of this upper part of the Hamilton belong to the Lower varcus Subzone of Givetian age.
The lower part of the Hamilton may possibly contain conodonts of the ensensis Zone, which straddles the Eifelian-Givetian boundary.
The Upper Devonian black shales of the Kettle Point Formation lie disconformably on the Ipperwash Formation. Kettle Point conodonts are assignable to the Middle asymmetricus Zone to possibly the costatus Zone (Winder, (966), thus demonstrating that almost the entire Upper Devonian (ranging in age
from early Frasnian to late Famennian) is represented in the subsurface.
The Devonian conodonts of southwestern Ontario were among the earliest to be studied in North America (Hinde, 1879; see also Bergstrom and Hansen, 1979). In the present study, one new species, Icriodus hankae, is introduced.
