OF CENTRAL CANADA PART V. 327 



area or oil district of Western Canada, although the deeper borings, 

 from which the petroleum is chiefly obtained, appear to pass through 

 its strata into the underlying Corniferous formation. Natural 

 springs have been noticed in various parts of the district, as in Mosa, 

 Enniskillen, Zone, Orford, etc. In the township of Enniskillen, 

 overflows from springs of this kind have formed deposits of solid 

 bitumen or " mineral tar," varying in thickness from an inch or two 

 to nearly a couple of feet, and extending over an acre or more of 

 ground. One of these deposits or " gum beds," in the northern part 

 of the township, is covered by several feet of Drift clay ; and in 

 places it presents a leafy or shaly texture, and contains impressions of 

 leaves and insects. As proved by the very different results obtained 

 in many instances from closely contiguous borings, the petroleum is 

 evidently confined to comparatively narrow and tortuous channels, 

 within limited belts of country. These belts are characterized, both 

 in the United States and Canada, by the presence of anticlinals, by 

 which a more or less fissured condition of the strata has been pro- 

 duced. The petroleum in these fissures is almost always accompanied 

 by salt or brackish water, and inflammable gas is usually emitted on 

 the first tapping of the fissure. As a rule, the wells become gradu- 

 ally impoverished, and frequently end by yielding water only. The 

 petroleum, as first obtained, is of a dark colour and more or less 

 viscid consistency. When decolourized and purified it loses about 

 forty per cent five barrels of crude oil yielding about three barrels 

 of refined oil. 



The Portage, or Portage-Chemuny Formation, as seen in Canada, 

 is made up of dark bituminous shales, holding in places large cal- 

 careous concretions, and also much iron pyrites, with occasional fish- 

 scales and spines, and impressions of long-flattened stems of a calamite 

 (fig. 1 19). Here and there these shales become coated, by weathering, 

 with a yellow crust of oxalate of iron. The formation extends pro- 

 bably over a considerable area around Lake St. Clair and the adjoin- 

 ing country ; but it is thickly overlaid by Drift and superficial depobits 

 throughout the greater part of this area, and the only well-recognized 

 exposures occur at Kettle-point, or Cape Ipperwash, in the township 

 of Bosanquet, 011 Lake Huron, and at one or two places in the town- 

 ships of Warwick and Brooke. As seen at these spots, the thickness 

 of the formation does not exceed twelve or fifteen feet. 



