422 T. 8. Hunt— Oil-hearing Limestone of Chicago, 



The objections to this view of the origin and geological rela- 

 tions of petroleum have been for the most part founded on 

 incorrect notions of the geological structure of southwestern 

 Ontario, which has afforded me peculiar facilities for stuthing 

 the question. In this region, it has been maintained by Win- 

 chell that the source of the petroleum is to be sought in the 

 Devonian pjroschists. I however showed in 1866, as the re- 

 sult of careful studies of the various borings : first, fnat none 

 of the oil-wells were sunk in the Grenes^e slates, but along 

 denuded anticlinal s where these rocks have disappeared, and 

 where, except the thin layer of Marcellus slate sometimes met 

 with at the base of the Hamilton shales, no pyroschists are 

 found above the Trenton limestone. Second, that the resen^oirs 

 of petroleum in the wells sunk into the Hamilton shales 



cent borings, only in the underlying Comiferous. Exam} 

 of this have been cited by me in wells in Enniskillen, Both- 

 well, Chatham and Thamesville, where petroleum has first been 

 found at depths of from thirty to one hundred and twenty feet 

 in the Comiferous limestone, in all of these places overlaid 

 by the Hamilton shales. It was also shown, that in two locali- 

 ties in this region, viz., at Tilsonburg and in Maidstone, where 

 the Comiferous is covered only by quaternary clays, petroleum 

 in considerable quantities has been obtained by sinking into 

 the limestone.* That the supplies of petroleum in such locali- 

 ties are less abundant than in parts where a mass of shales and 

 sandstones overlies the oil-bearing limestone is explained bj 

 the fact that both the pores and the fissures in the superior 

 strata serve to retain the oil, in a manner analogous to the 

 quaternary gravels in some parts of this region, which are the 

 sources of the so-called surface oil-wells. It is, therefore, no 

 surprising that examples of pyroschists impregnated with oil 

 should sometimes occur, but the evidence of the existence oi 

 indigenous petroleum, which is so clear in the vanous lime- 

 stones, is wanting in the case of the pyroschists ; although con- 

 cretions holding petroleum, have been observed in the Mar- 

 cellus and the Genesee slates of New York. There is, how- 

 ever, reason to believe, as I have elsewhere pointed out, tfla 

 much of the petroleum of Pennsylvania, Ohio, and the ^^^^^^ 

 regions, is indigeneous to certain sandstone strata in the i>ev^ 

 ian and Carboniferous rocks, f , a j. 



At the meeting of the American Association for the a^ 

 vancement of Science at Chicago, in August, 1868, m * ^ 

 cussion which followed the reading of a paper ty myseu 

 the geology of Ontario,^ it was contended that, althougQ 

 * This Jour. IT, ilvi, 360; and Report Geol., Canada, 1866, pp. }^}i^^^- 

 f Ibid. 240. X This Jour. II, xlvi, d&o- 



