424 T. S. Hunt — Oil-bearing Limestone of Chicago. 



suspended, was "935 at 16° C. Estimating tlie density of the 

 somewhat porous dolomite at 2-600, we have the equation 

 •935 : 2-600 : : 1-537 : 4-26; so that the volume of the petro- 

 leum obtained equalled 4-26 per cent of the rock. This result 

 is evidently too low for two reasons ; first, because the rock had 

 already lost a part of its oil, while in the quarry and subse- 

 quently, before its examination : and secondly, because the more 

 volatile portions had been dissipated in the process of extrac- 

 tion 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 fol- 

 lowing calculations. A layer of this oleiferous dolomite one 

 mile (5280 feet) square, and one foot in thickness will contain 

 1,184,882 cubic feet of petroleum, equal to 8,850,069 gallons 

 " '""" cubic inches, and to 221,247 barrels of forty gallons 



lie geological condi- 

 a of the oil from such 

 ufT certain anticlinal 



each. Taking the minimum thickness of thirty -five feet, as- 

 signed 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 petroleum, or less than 

 would be contained in four square miles of the oil-bearing 

 limestone band of Chicago. 



It is not here the place to insist upon the , 

 tions which favor the liberation of a portio 

 rocks, and its accumulation in fissures alo 

 lines in the broken and uplifted strata, inese poiute i" "- 

 geological history of petroleum were shown by me in my ursj 

 publications already referred to, March and July, 1861, ana 

 independently, about the same time, by Prof E. B. Andrews 

 in this Journal for July, 1861.* , 



The proportion of petroleum in the rock of Chicago m&j ^ 

 exceptionally large, but the oleiferous character of great tliicK- 

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

 be seen from the above calculations that a very small propor_ 

 tion of the oil thus distributed would, when accumulated along 

 lines of uplift in the strata, be more than adequate to the sup 

 ply of all the petroleum wells khown in the regions wtiere 

 these oil-bearing rocks are found. With such sources exis^ 

 ing ready formed in the earth's crust, it seems to me, to say 

 least, unphilosophical to search elsewhere for the ongin u 

 petroleum, and to imagine it to be derived by some une 

 plained process from rocks which are destitute of the s 



* This Journal II, ixiii, 85. See also papers on the subject by J^"" ,^ ^ 

 Prof. Evans, Ibid. II. xl. 33, 334; and one bj the author, H, xixv, H". 

 Report Geol. Survey of Canada, 1866, pp. 266-257. 



