No. 1.] HUNT — OIL-BEARING LIMESTONE. 59 



quarry, and subsequently, before its examination ; and secondly, 

 because the more volatile portions had been dissipated in the 

 process of extraction just described. 



In assuming 100-00 parts of the rock to hold 4*25 parts by 

 volume of petroleum, we are thus below the truth in the following 

 calculations. A layer of this oleiferous dolomite one mile (5280 

 feet) square, and one foot in thickness will contain 1,184,832 

 cubic feet of petroleum, equal to 8,850,069 gallons of 231 cubic 

 inches, and to 221-247 barrels of forty gallons each. Taking the 

 minimum thickness of thirty- five feet, assigned by Mr. Worthen 

 to the oil-bearing rock at Chicago, we shall have in each square 

 mile of it 7,743,745 barrels, or in round numbers seven and 

 three quarter millions of barrels of petroleum. The total produce 

 of the great Pennsylvania oil-region for the ten years from 1860 

 to 1870 is estimated at twenty-eight millions of barrels of petro- 

 leum, or less than would be contained in four square miles of the 

 oil-bearin2; limestone band of Chicao-o. 



It is not here the place to insist upon the geological conditions 

 which favour the liberation of a portion of the oil from such rocks, 

 and its accumulation in fissures along certain anticlinal lines in 

 the broken and uplifted strata. These points in the geological 

 history of petroleum were shown by me in my first publications 

 already referred to, March and July, 1861, and indejDendently, 

 about the same time, by Prof. E. B. Andrews in this Journal for 

 July, 1861.^'^ 



The proportion of petroleum in the rock of Chicago may be 

 exceptionally large, but the oleiferous character of great thick- 

 ness of rock in other regions is well established, and it will be 

 seen from the above calculations that a very small proportion of 

 the oil thus distributed would, when accumulated along lines of 

 uplift in the strata, be more than adequate to the supply of all 

 the petroleum wells known in the regions where these oil-bearing 

 rocks are found. With such sources existing ready formed in the 

 earth's crust, it seems to me, to say the least, unphilosophical to 

 seach elsewhere for the origin of petroleum, and to imagine it to 

 be derived by some unexplained process from rocks which are 

 destitute of the substance. 



* Sill. Jour. II, xxxii, 85. See also papers on the subject by 

 him and by Prof. Evans, Ibid. II, xl. 33, 334 ; and one by the author, 

 II, XXXV, 170 ; also Report Geol. Survey of Canada, 1866, pp. 256-257. 



