76 PROCEEDINGS OP THE WASHINGTON MEETING 



they were in reality the same forms. These may have been internal molds 

 loosened from the Anderdon and incorporated into the Onondaga at the time 

 the latter was being deposited. 



There is thus an accumulation of positive evidence demonstrating the exist- 

 ence of a period of erosion of long duration at the basal contact of the 

 Onondaga in the Amherstburg quarry, and very similar evidences may be 

 found on the Michigan side of the river. It is, of course, impossible to say 

 positively that the sand at the contact represents the Oriskany in this region. 

 remote from any known deposits of that formation, or that it is even material 

 derived from the erosion of an Oriskany deposit, as is certainly the case farther 

 northeast in Ontario. It is equally possible that the sand at Amherstburg 

 was derived from outcrops of the Sylvania. subjected to erosion in pre-Onon- 

 daga time, since the Onondaga (Dundee) limestone is in contact with the 

 Sylvania sandstone at the National Silica Company's quarry. 7 miles north- 

 west of Monroe. Michigan/' and hence may have a similar relation at other 

 near-by localities. It should be pointed out also that the Onondaga of extreme 

 southwestern Ontario, like the Columbus limestone of northern Ohio, probably 

 does not represent the whole of the formation as developed in western New 

 York. In Ontario, immediately across the Niagara River from Buffalo, where 

 the Onondaga limestone is probably the exact equivalent of the same deposit 

 in New York, the lower layers are characterized by the relative absence of 

 corals and the abundance of brachiopods. Some of the most characteristic 

 fossils of this horizon are Amphigenia elongata, Anophia nucleate, Anoplotheca 

 Camilla, Gentronella glansfagea, Ghonetes hemisphericus, Cypricardinia in- 

 denta, Platyceras dentalium, and numerous others that are abundant at higher 

 horizons. The beds carrying these species have been traced across the prov- 

 ince and are last found near the shore of Lake Huron to the south of Port 

 Elgin. These species are not found in the Onondaga at Goderich or at Am- 

 herstburg; neither are they found in the outcrops on the islands of Lake Erie 

 and at Marblehead. The probability is that the beds which should contain 

 them were never deposited in those regions, and that the lowest Onondaga is 

 wanting. Some of these species reappear in the Columbus limestone of central 

 Ohio, where the Onondaga fauna is again more like that of western New York. 



It. is therefore evident that the time interval represented by tbe uncon- 

 formity (disconformity) between the Anderdon limestone and the Onondaga 

 was a long one. If we may trust the record of tbe Goderich well, as described 

 by Hunt, and the excellent section of the Oakwood salt shaft, tbe stratigraphic 

 order as given by Sherzer and Grabau cannot be disputed. The period of 

 erosion at Amherstburg therefore removed all the Lucas and Amherstburg 

 dolomites and lasted through as much of the Onondaga as is represented by 

 the lower zone of that formation at the eastern end of Lake Erie. Tbe par- 

 ticular division of the Detroit River series which shows most marked Middle 

 Devonian faunal characters therefore preceded its derivative fauna, tbe Onon- 

 daga, by the Lucas dolomite interval and this long erosion period. If tbe 

 arenaceous material at the base of the Onondaga at Amherstburg and near-by 

 localities in Michigan represents the Oriskany horizon, as believed by Sherzer 



8 W. H. Sherzer and A. W. Grabau: Geol. and Biol. Survey Michigan', Pub. 2, Geol. 

 •r. 1, 1009 (1910), p. 40. 



