WHifE: rely^lTions between coal and petroleum 205 



Cretaceous beds, associated with or underlying sub-bituminous 

 coals, show gravities averaging about 35° or 36°. In the Evans- 

 ton region, where the oils range from 38° to 43°, the coals of 

 the overlying formation are reported to be of high sub-bituminous 

 rank. 



In Utah and Colorado, the oils of the Green River formation, 

 in which the carbonaceous deposits have not passed the lignitic 

 stage, are of low rank, having gravities of 26° or less; but the 

 oils found in the Rangeley field, in Cretaceous strata beneath 

 rocks containing medium rank bituminous coal in the same basin, 

 show a gra^dty of 43° which corresponds to the stage of the 

 alteration of the coals. In the Florence oil field in Colorado, 

 oils averaging 30° or 31° are found in shales underlying coals 

 of very low bituminous rank. Oil of 39° gravity in the Boulder 

 coal field is said to occur in the Pierre shale at depths of more 

 than 2000 feet below the base of the Laramie of the region, in 

 which the coals, of high sub-bituminous rank at Marshall, appear 

 to be progressing in alteration westward toward the oil field. 



The broad area of almost undisturbed upper Paleozoic strata 

 in the Mississippi Valley and middle States offers an unrivalled 

 field for the study of petroleum with reference to the regional 

 alteration of the carbonaceous deposits. In eastern Kansas the 

 oils, which occur in Pennsylvanian strata carrying coals of very 

 low bituminous rank, range, for the most part, from 32° to 34° 

 in gravity, though in passing southward to the O^ahoma line 

 and onward through the Osage Nation and beyond the Glenn 

 pool, the oils show an increase in average gravity;^' those in 

 the Osage region ranging, in general, from 33° to 36°. Farther 

 southeastward the gravities rise to 39° or 40° at the edge of the 

 developed field. 



The Madill oil, found in the basal sands of the Cretaceous, 

 undoubtedly owes its low gravity, 47°, to its source in the imme- 

 diately underlying Pennsylvanian strata, which are tilted and 

 compressed in the Arbuckle uplift. 



In the coal fields of Illinois and Indiana, where the coals are 

 of low bituminous rank, but somewhat better than those of 



1- See R. H. Wood, U. S. Geol. Survey, Bull. 513: 36. 1913. 



