12 THE CANADIAN NATURALIST. [March 



times called the Upper Helderberg, and consisting of the Oriskany, 

 with its overlying Corniferous limestone (embracing the local sub- 

 division known as the Onondaga limestone) constitutes what may 

 be provisionally called the Lower Devonian. The second group 

 has for its base the black pyroschists known as the Marcellus 

 shale, followed by the Hamilton shale, with the local TuUy 

 limestone, and terminated by another band of black pyroschist, the 

 Genesee slate ; the whole constituting what may be termed 

 the Middle Devonian. The third group, embracing the Portage 

 and the Chemung shales and sandstones, with the local Catskill 

 sandstone, makes the Upper Devonian. (*) 



The black Genesee slate, according to Mr. Hall, is paleontologi- 

 cally related to the Hamilton slates, and by him included as part 

 of the Hamilton group, as recognized in the Geology of Canada. 

 Similar black slates, though thicker, less fissile, and interstratified 

 with greenish arenaceous beds, occur at the base of the Portage 

 formation, marked by the remains of land-plants and of fishes 

 which characterize the Upper Devonian. The black slates of this 

 horizon thus constitute, as it were, beds of passage. The 

 thickness of the lower and more fissile black beds, recognized 

 by Mr. Hall as belonging to the Hamilton group, is, according to 

 him, only twenty-four feet at the eastern end of Lake Erie. 



There exists in south-western Ontario, along the River St. Clair, 

 an area of several hundred square miles underlaid by black shales, 

 in the counties of Lambton and Kent, of which only the lower 

 part belongs to the Hamilton group. These strata are exposed in 

 very few localities, but the lower beds are seen in Warwick, where 

 they were, many years since, examined by Mr. Hall, in company 

 with Mr. Alexander Murray of the Geological Survey of Canada, 

 and were by the former identified with the Genesee slate forming 

 the summit of the Hamilton group. They are in this place, 

 however, overlaid by more arenaceous beds, in which Prof. Hall 

 at the same time detected the fish remains of the Portage 

 formation. The thickness of these black strata, as appears from 

 a boring in the immediate vicinity, is fifty feet, beneath 

 which are met the gray Hamilton shales. A similar section 

 occurs at Cape Ipperwash or Kettle Point in Bosanquet, on Lake 

 Huron, where bands of alternating greenish and black arena- 



(*) .Tames Hall, in Foster & Whitney's Geology of Lake Superior, ii, 

 336. 



