1869.] HUNT — GEOLOGY OF SOUTH-WESTERN ONTARIO. 19 



pointed out by uie in 18G1. The conditions under which oil 

 occurs in these limestones in Ontario are worthy of notice, inas- 

 much as they present grave difficulties to those who maintain 

 that petroleum has been generated by an unexplained process of 

 distillation going on in some underlying hydrocarbonaceous rock. 

 Numerous borings in search of oil on Manitoulin Island, have 

 been carried down through the Utica and Loi'aine shales, but 

 petroleum has been found only in fissures at considerable depths 

 in the underlying limestones of the Trenton group. The supplies 

 from this region have not hitherto been abundant, yet from one 

 of the wells just mentioned, 120 barrels of petroleum were 

 obtained. The limestone here rests on the white unfossiliferous 

 Chazy sandstone, beneath which are found only ancient crystalline 

 rocks, so that it is difficult to avoid the conclusion that this lime- 

 stone of the Trenton group is, like those of Upper Silurian and 

 Devonian age, already noticed, a true oil-bearing rock. 



In concluding these observations on the geology of Ontario, it 

 may be remarked that throughout the south-western counties, the 

 distribution of the Middle and Upper Devonian rocks has been 

 determined almost wholly from the results of borings undertaken 

 in search of petroleum. From these it appears that the wide 

 spread of these rocks in this region is connected, first, with a 

 transverse north and south synclinal depression, which traverses the 

 peninsula, and has been noticed in the Geology of Canada, p. 3(JiJ, 

 and secondly, with several small undulations, running north-east 

 and south-west, on the north west side of the anticlinal of the 

 Thames; which is a prolongation of that passing by Cincinnati, 

 and may be -regarded as part of the main anticlinal of the great 

 axis of elevation which divides the coal field of Pennsylvania from 

 that of Michigan. 



The Devonian rocks are found, in the region under considera- 

 tion, at depths not only far beneath the water-level of the adja- 

 cent lakes of Erie and St. Clair, but actually below the horizon 

 of the bottom of those shallow lakes. Thus at Vienna, in Bay- 

 ham, at a point said to be about forty feet above the level of Lake 

 Erie, the underlying rock was met with beneath 240 feet of clay, 

 while at Port Stanley, twenty feet above the lake, the Hamilton 

 shale was struck beneath 172 feet of clay, and at the Rondeau, 

 just above the level of Lake Erie, the clay was 104 feet thick. 

 A similar condition of things exists on the south side of the lake, 

 at Cleveland, where no rock is encountered at a depth of 100 feet 



