49 



record. Here and there fairly well developed anticlines 

 and synclines appear, while at other places the rock seems 

 to lie nearly flat. 



The southern part of the Port Colborne region is 

 underlain by the Onondaga limestone, while the Cobleskill 

 dolomite (Silurian) and the Salina beds (Silurian) occur 

 immediately under the surface deposits to the north. 

 These latter form but meagre outcrops although they are 

 reached by the drill in boring for gas. [6] Great heaps of 

 the Silurian rocks, removed during the construction of 

 the Welland canal, may be seen to the northward from 

 the village of Humberstone. These formations include 

 dolomitic beds and shales of varying thicknesses. 



The Onondaga was formerly called the Corniferous 

 limestone [5] because of the abundance of chert which it 

 contains. While chert is a striking characteristic of this 

 formation in Ontario near the eastern end of Lake Erie, 

 it is rare or absent in the same beds which outcrop along 

 the Detroit river and on the islands to the south It is 

 a most variable formation in its physical appearance. At 

 the Port Colborne locality its upper portion is a dark 

 bluish to brownish black limestone containing a great 

 quantity of dark coloured chert. Just below this, and 

 sometimes separated by a very sharp line, is a highly 

 calcareous, semi-crystalline limestone filled with corals. 

 This rock grades into beds of less purity, as the lower 

 portion of the formation is approached, while the basal 

 part is a conglomerate [9] (shown only in the bottom of 

 the Welland canal) of Silurian pebbles mingled with sand 

 and calcareous mud. The Onondaga limestone is abund- 

 antly fossiliferous. Many of the fossils are silicified and 

 stand out in relief with most of the structures preserved 

 as the limestone weathers away under the thin coating of 

 drift. Corals are most plentiful and these are often so 

 numerous as to form true reefs. These coral beds may be 

 traced westward from Fort Erie to Villa Nova — a distance 

 of over 45 miles (72-44 km.) Many of the types described 

 by E. Billings and James Hall, were obtained in the vicinity 

 of Port Colborne. 



SECTIONS OF THE ONONDAGA. 



The Hogan Quarry. This quarry now abandoned 

 but under the control of the Canadian Portland Cement 

 35066—4 



