STATE GEOLOGIST. 13 



These shales, at Enniskillen, Bear Creek and neighboring 

 localities in Canada, become the source of large quantities of 

 petroleum; and there is little doubt that the mineral oil of Ohio 

 is derived from the same formation.* These shales, and the 

 great mass of less bituminous shales lying above them, contain 

 a vast amount of vegetable or animal matter, the source of the 

 rock oils. This oil is eliminated by a slow spontaneous distil- 

 lation, and rises up and saturates the overlying porous sand- 

 stone rocks, in which, in Ohio and Pennsylvania, it is found by 

 boring. 



Does the rock oil exist in Michigan? The oil bearing rocks 

 of Enniskillen, are but an elbow of a formation which belongs 

 properly to the Michigan side of the boundary line. The oil 

 producing shales unquestionably dip under our State, and are 

 not far from the surface throughout St. Clair, Oakland, Macomb, 

 Sanilac and Huron counties But are they overlain by a 

 porous sandstone capable of becoming the repository of the 

 products of the spontaneous distillation of the oil, or are they 

 overlain by argillaceous strata which would prove completely 

 impervious to the ascent of volatile matters? In the present 

 state of our knowledge this. question cannot be satisfactorily 

 answered, but the indications are not altogether favorable. 

 Nevertheless it is well known that at several points in St. Clair 

 county evidences of bituminous exudations exist, and streams 

 of inflammable gas have escaped from the earth; moreover, an 

 overlying sandstone does not seem to be everywhere an essen- 

 tial condition to the accumulation of oil. In the present state 

 of the case there seems to be sufficient encouragement to em- 

 bark in explorations on a cautious scale. 



ihe strike of the black bituminous shales beneath the bed of 

 the lake, from Thunder Bay to Kettle Point, must pass several 

 miles to the east of Point aux Barques. It follows, therefore, 

 that the shales and flagstones occurring along the shores of 

 Huron county and dipping toward the south-west, must be many 



*See an interesting paper on the "Rock Oils of Ohio," by Dr. J. S. Newberry, extracted 

 from the Ohio Agricultural Report for 1859. 



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