XIII. ] GEOGNOSY OF THE APPALACHIANS. 259 



closely related genus, which he has named Olenellus, and which 

 is now regarded as belonging to the horizon of the Potsdam 

 sandstone, to which we shall presently advert. 



Further studies of the fossiliferous rocks near Quebec showed 

 the existence of a mass of sediments estimated at about 1,200 

 feet, holding a numerous fauna, and corresponding to a great 

 development of strata about the age of the Calciferous and 

 Chazy formations, or, more exactly, to a formation occupying a 

 position between these two, and constituting, as it were, beds 

 of passage between them. In this new formation were in- 

 cluded the graptolites already described by Hall, and the 

 numerous Crustacea and brachiopoda described by Billings, all 

 of which belong to the Levis slates and limestones. To these 

 and their associated rocks Sir William Logan then gave the 

 name of the Quebec group, including, besides the fossiliferous 

 Levis formation, a great mass of overlying slates, sandstones, 

 and magnesian limestones, hitherto without fossils, which have 

 been named the Lauzon rocks, and the Sillery sandstones and 

 shales, which he supposed to form the summit of the group, 

 and which had afforded only an Obolella and two species of 

 Lingula ; * the volume of the whole group being about 7,000 

 feet. 



The paleontological evidence thus obtained by Billings and 

 by Hall, both from near Quebec and in Vermont, led to the 

 conclusion that the strata of these regions, so much resembling 

 the upper members of the Champlain division, were really a 

 great development, in a modified form, of some of its lower por- 

 tions. Their apparent stratigraphical relations were explained 

 by Logan by the supposition of " an overturned anticlinal fold, 

 with a crack and a great dislocation running along the summit, 

 by which the Quebec group is brought to overlie the Hudson 

 Eiver group. Sometimes it may overlie the overturned Utica 

 formation, and in Vermont points of the overturned Trenton 

 appear occasionally to emerge from beneath the overlap." He, 

 at the same time, declared that " from the physical structure 

 alone, no person would suspect the break that must exist in 

 * See Billings, Palaeozoic Fossils of Canada, p. 69. 



