No. 1.] GEOLOGICAL SURVEY 01^ CANADA. 77 



portion of the region in Ontario underlaid by tliis formation, it is 

 so much concealed that it is not easy to determine its thickness. 

 If we may conclude from the boring at Clinton, it would seem to 

 be in that locality not far from 200 feet. In the numerous bor- 

 ins^s which have been sunk throus-h this limestone, there is met 

 with nothing distinctive to mark the separation between it and 

 the limestone beds which form the upper part of the Onondaga 

 or Salina formation, and consist of dolomite, alternating with beds 

 of a pure limestone like that of the Corniferous formation. The 

 saliferous and gypsiferous soft magnesian marls, which form the 

 lower part of the Onondaga formation are, however, at once recog- 

 nized by the borers, and lead to important conclusions regarding 

 this formation in Ontario. 



At Tilsonburs:, a borins; showed the existence of the Corniferous 

 limestone directly beneath about forty feet of clay, while in an- 

 other boring, about two miles to the south-west, it was overlaid 

 by a few feet of soft shales, probably forming the basis of the 

 Hamilton formation. The first boring at Tilsonburg, as mentioned 

 in the report for 1866, was carried to a depth of 854 feet in the 

 solid rock. Numerous specimens of the borings from the first 

 196 feet, were of pure non-magnesian limestones, but below that 

 depth similar limestone alternated with dolomite. The marls 

 which occur at the base of the Onondaga formation were not met 

 with in this boring, though the water from 854 feet was said to 

 be strongly saline. I was informed by the proprietors, Messrs. 

 Hebbard & Avery, that the well furnished, by pumping, a brine 

 marking from 35^^ to 50° of the salometer, but I was not able to 

 get any of the water, and the well was soon after abandoned, al- 

 though the presence of so strong a brine would seem to show the 

 proximity of a saliferous stratum. 



In a boring at London, where the presence of the base of the 

 Hamilton was marked by about twenty feet of gray shales, in- 

 cluding a band of black pyroschist, overlying the Corniferous, 600 

 feet of hard rock were passed through before reaching soft mag- 

 nesian marls, which were penetrated to the depth of seventy-five 

 feet. Specimens of the borings from this well, and from another 

 near by, carried 300 feet from the top of the Corniferous, show 

 that pure limestones are interstratified with the dolomites to a 

 depth of 400 feet. At Tilsonburg a pure limestone was met with 

 at 524 feet from the top. 



At St. Mary's, 700 feet, and at Oil Springs in Enniskillen, 



