No. 1.] HUNT— OIL-BEARING LIMESTONE. 55 



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 pyrogenous 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, peat, lignite, coal, and 

 most substances of organic origin, and has led to their being- 

 called bituminous, although they are not in any proper sense 

 bituminiferous. The distinction is one which will at once be 

 obvious to all those who are familiar with chemistry, and who 

 know that pyroschists are argillaceous rocks containing in a state 

 of admixture a brownish insoluble and infusible hydrocarbonace- 

 ous matter, allied to lignite or to coal.^ 



Second, the pyroschists of these different formations do not, so 

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

 exposed at the surface or brought up by borings from depths of 

 many hundred feet, present any evidence of having been sub- 

 mitted to the temperature required for the generation of volatile 

 liydrocarbons. On the contrary they still retain the property of 

 yielding such products when exposed to a sufficient heat, at the 

 same time undergoing a charring process by which their brown 

 colour is changed to black. In other words these pyroschists 

 have not yet undergone the process of destructive distillation. 



Third, the conditions which the oil occurs in the limestones, 

 are inconsistent with the notion that it has been introduced into 

 these rocks by distillation. The only probable or conceivable 

 source of heat, in the circumstances, being from beneath, the 

 process of distillation would naturally be one of ascension, the 

 more so as the pores of the underlying strata would be filled with 

 water. Such being the case, the petroleum of the Upper Silurian 

 and Lower Devonian limestones must have been derived from the 

 Utica slate beneath. This rock, however, is ualtered, and more- 

 over, the intermediate sandstones and shales of the Loraiue, Me- 

 dina and Clinton formations, are destitute of petroleum, which 

 must, on this hypothesis, have passed through all these strata to 

 condense in the Niagara and Corniferous limestones. More than 

 this, the Trenton limestone which, on Lake Huron and elsewhere, 

 has yielded considerable quantities of petroleum, has no pyroschists 

 beneath it, but on Lake Huron rests on ancient crystalline rocks, 



* Silliman's Journal, II, xxxv, 159-lGl. 



