SILURIAN FORMATIONS OP ONTARIO. 231 



Guelph. — Underneath the Onondaga, is met with, over a considerable 

 portion of the province, a series of yellowish to brown and in places 

 bituminous dolomites, having a probable thickness of not more than 160 

 feet and known as the Guelph formation. These beds have been pierced 

 in many wells in Ontario, but efforts to obtain from drillers definite in- 

 formation as to their thickness and character have been useless, nor has 

 it been found possible to draw any distinction, in records of wells so far 

 obtained, between the dolomites of this formation and the gray dolomite 

 of the Niagara, which immediately underlies it. In the wells of the Bertie 

 township, Welland county, gas field are found about 240 feet of dolomites 

 of Guelph and Niagara age, and in number 1 well sunk by the Port 

 Colborne Natural Gas Light and Fuel company in Humberstone town- 

 ship, Welland county, there are found, according to the driller, 30 feet 

 of shaly dolomite and 188 feet of brown dolomite, with dark-blue shales 

 toward the bottom. In the town of Paris a well was sunk in which 99 

 feet of Guelph dolomite was found immediately underlying the Onon- 

 daga. The boring was not continued beyond this depth, so it is impos- 

 sible to say what thickness the formation attained at this point. 



Niagara. — The Niagara formation, the upper beds of which are com- 

 posed of dolomites, as stated above, has a probable thickness in Welland 

 county of about 140 feet, made up of gray dolomites reposing upon about 

 50 feet of dark shale. It extends throughout the province in a north- 

 westerly direction to Cabotshead, where, according to the Geology of 

 Canada, 1863, it would have a thickness of about 450 feet, and is com- 

 posed of a whitish subcrystalline limestone. On the Welland canal, near 

 Thorold, is seen the following section in ascending order:* 



Bluish-black bituminous shale 55 feet. 



Bluish-gray argillaceous limestone 8 " 



Dark bluish bituminous limestone 8 " 



Light and dark -gray magnesian limestone 20 " 



Bluish bituminous limestone 7 " 



Total 104 " 



This section does not include two 10-foot beds of bluish-gray magne- 

 sian limestone which maybe of Clinton age, though toward their summit 

 holding two species of fossils characteristic of the Niagara series in New 

 York, nor does it reach the summit of the formation. In Essex county 

 the beds met with in the various wells sunk near Kingsville and Ruth- 

 ven at a depth of from 1,000 to 1,100 feet consist of a light yellowish-gray 

 vesicular dolomite which is probably of Niagara age. It is from this 

 dolomite that the lame flows of gas have been obtained. 



I Geology of Canada, 1863, p. 322. 



