T. S. Hunt — Oil-hearing Limestone of Chicago. 



When in 1861,* I first published my views on the petroleum 

 of the West, I expressed the opinion that the true source of it 

 was to be looked for in certain limestone formations which had 

 long been known to be oleiferous. I referred to the early ob- 

 servations of Eaton and Hall on the petroleum of the Niagara 

 'limestone, to numerous instances of the occurrence of this sub- 

 stance in the Trenton and Corniferous formations and, in 

 Gaspe, in limestones of Lower Helderberg age. Subsequently, in 

 this Journal for March, 1863, and in the Geology of Canada, 

 I insisted still further upon the oleiferous character of the 

 Corniferous limestone in southwestern Ontario, which appears 

 to be the source of the petroleum found in that region. I may 

 here be permitted to recapitulate some of my reasons for con- 

 cluding that petroleum is indigenous to these limestones, and for 

 rejecting the contrary opinion, held by some geologists, that its 

 occurrence in them is due to infiltration, and that its origin is 

 to be sought in an unexplained process of distillation from 

 pyroschists or so-called bituminous shales. These occur at 

 three distinct horizons in the New York system, and are known 

 as the Utica slate, immediately above the Trenton hmestone, 

 and the Marcellus and Genesee slates which lie above and 

 below the Hamilton shales ; the latter being separated from the 

 underlying Corniferous limestone by the Marcellus slate. 



First, these various pyroschists do not, except in rare instances. 

 contain any petroleum or other form of bitumen. Their capa- 

 bility of yielding volatile liquid hydrocarbons or_ pyrogenou^ 

 oils, allied in composition to petroleum, by what is known to 

 chemists as destructive distillation, at elevated temperatures, is 

 a property which they possess in common with wood, pea- 

 lignite, coal, and most substances of organic origin, and na^ 

 led to their being called bituminous, although they are not m anj 

 proper sense bituminiferous. The distinction is one which wi 

 at once be obvious to all those who are familiar with chemistr} . 

 and who know that pyroschists are argillaceous rocks co^^i^^'}; 

 ing in a state of admixture a brownish insoluble and mtusiDit 

 hydrocarbonaceous matter, allied to lignite or to coaLf 



Second, the pyroschists of these different formations do no • 

 so far as known, in any part of their geological distribution, 

 whether exposed at the surface or brought up by bonngs iro 

 « Montreal Gazette, March 1, and Can. Natumlist, July, 1861. 



