T. S. Hunt— Oil-hearing Limestone of Chicago. 423 



various limestones wtich have been mentioned are truly oleifer- 

 ous, the quantity of petroleum whicli they contain is too incon- 

 siderable to account for the great supplies furnished by oil-pro- 

 ducing districts, hke that of Ontario for example. This opinion 

 being contrary to that which I had always entertained, I re- 

 solved to submit to examination the well-known oil-bearing 

 limestone of Chicago. 



This limestone, the quarries of which are in the immediate 

 vicinity of the city, is so filled with petroleum that blocks of 

 it which have been used in buildings are discolored by the 

 exudations, which mingled with dust, form a tarry coating 

 upon the exposed surfaces. The thickness of the oil-bearing 

 beds, which are massive and horizontal, is, according to Pro£ 

 Worthen, from thirty-five to forty feet, and they occupy a po- 

 sition about mid-way in the Niagara formation, which has in 

 ihis region a thickness of from 200 to 250 feet As exposed 

 m the quarry, the whole rock seems pretty uniformly saturated 

 with petroleum, which exudes from the natural joints and the 

 fractured surfaces, and covers small pools of water in the de- 

 pressions of the quarry. I selected numerous specimens of the 

 rocks from different points and at various levels, with a view 

 of getting an average sample, although it was evident that they 

 bad already lost a portion of their original content of petroleum. 

 After lying for more than a year in my laboratory they were 

 submitted to chemical examination. The rock, though porous 

 and discolored by petroleum, is, when freed from this substance, 

 a nearly white, granular, crystalline and very pure dolomite, 

 yielding 54-6 p. c. of carbonate of lime. 



-1-wo separate portions, each made up of fragments obtained 

 by breaking up some pounds of the specimens above mentioned, 

 and supposed to represent an average of the rock exposed m 

 n7 a^any, were reduced to coarse powder in an iron mortar, 

 y these two portions, respectively, 100 and 138 grammes were 

 ^^en, and were dissolved in warm dilute hydrochloric acid, 

 ihe tarry residue which remained in each case, was carefully 

 collected and treated with ether, in which it was readily solu- 

 te with the exception of a small residue. This, in one of the 

 ^Ples, was found equal to 40 p. c, of which 13 was volati- 

 ^ed by heat with the production of a combustible vapor hav- 

 3 a fatty odor; the remainder was silicious. The brown 

 etbenal solutions were evaporated, and the residuum, freed 

 ^om water and dried at 100° C, weighed in the two expen- 

 ^ents equal to 1-570 and 1-505 per cent of the rock, or a m^n 

 nri! A^' ^^ ^^ a viscid reddish-brown oil, which, though de- 

 M °f i*s niore volatile portions, stUl retained somewhat of 

 Be^^'^^ petroleum, which is so marked in the rock It8 

 Wc gTavity, as determined by that of a mixture of alcohol 

 ^^d water, in which the globules of the petroleum remained 



