'6 A POPULAR EXPOSITION OF THE 



pied by these Middle and Upper Silurian formations, but their strata 

 are mostly concealed by Drift- deposits. The localities in which in- 

 structive exposures occur, have been mentioned under. the separate 

 descriptions of each formation, at the commencement of this Part of 

 our Essay. The Clinton beds near the mouth of the Niagara River 

 are only a few feet in thickness, but they ^increase towards the north- 

 west, and attain, on the shores of Georgian Bay, a thickness of about 

 180 feet. The Niagara formation increases in the same direction, 

 from about 240 or 250 feet, to probably about 400 feet. The Guelph 

 formation at its thickest part is estimated by Sir Wra. Logan at 160 

 feet. The Onondaga formation averages from 200 to 300 feet. 



Still further to the west, a thin band of sandstone, belonging to the 

 Oriskany Formation (Map : No. 15), crops out above the Eurypterus 

 beds in the townships of Bertie, Cayuga, &c. This forms the base of 

 the Devonian series. It is succeeded by a large development of the 

 cherty limestones of the Corniferous Formation, (No. 16), averaging 

 collectively about 200 (?) feet in thickness, and supposed to be the 

 source of the Petroleum supplies of that district. These are followed 

 by the encrinal limestone bands and calcareous shales of the Hamilton 

 (or Lambton) series (No. 17,) making up an additional thickness of 

 from 200 to 300 feet. Finally, at Kettle Point, and in the townships 

 of Warwick and Brooke, a few isolated patches of dark bituminous 

 shales, containing calaraites and fish-scales, conclude the Devonian 

 series as developed in this part of Canada. These bituminous shales, 

 are referred to the base of the Portage group (No. 18). The relations 

 of the Hamilton or Lambton shales to the underlying Corniferous 

 strata, and the chief points of interest belonging to the occurrence of 

 petroleum in this region, have already been sufficiently discussed. 



The Drift accumulations spread so generally over this western basin, 

 consist of thick beds of clay, overlaid in most places by deposits of 

 sand and gravel, with boulders of gneiss, syenite, limestone, and other 

 rocks. The thickness of the entire mass varies greatly, but in places 

 it exceeds 100 feet. In the upper Drift beds, or rather in those formed 

 out of Drift and other materials by Post-glacial influences, numerous 

 shells of existing fresh-water mollusks {planorbis, cyclas, &c.), occur 

 at different heights above our present lake-waters ; whilst there seems 

 to be an entire absence, in these beds, of marine or estuary types, such 

 as occur in deposits of a similar age in the St. Lawrence basin. Hence 

 the inference, that, at a comparatively recent geological period, our 



