ABSTRACTS 



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CEOLOQY.—The Mule Creek oil field, Wyoming. E. T. Hancock. 

 U. S. Geol. Survey Bull. 716-C. Pp. 19 (35-53), pl- i, %• i- 

 1920. 

 The bulletin discusses an area containing two well-developed anti- 

 clines about 30 miles S. S. E. of the Black Hills, near the east edge of 

 Wyoming in Niobrara County. Upper Cretaceous beds from the 

 top of the Niobrara formation down into the Mowry shale are exposed, 

 a stratigraphic thickness of about 1600 feet. The subsurface section, 

 compiled from records of drill holes in this and adjacent areas, includes 

 about 2700 feet of beds and extends 398 feet into the top of the Missis- 

 sippian. Structure is represented by contours at lOO-foot intervals. 

 The two anticlines described lie along the general trend of the Hartville 

 uplift, which connects the Front Range with the Black Hills, and strike 

 nearly due north. The length of one anticline is about 4 miles, of 

 the other more than 7 miles; the widths range from 2 to 5 miles or 

 more. The dips average from 5° to 15°, reaching a maximum of 26°. 

 No faults are noted. Active production in the field began early in 

 1919. The producing wells average 125 to 150 barrels and the total 

 production of the field early in 1920 exceeded 1000 barrels a day, of a 

 paraffin oil of low specific gravity. Tests on one of the anticlines had 

 been unsuccessful when the report was prepared. The writer lays 

 much stress as a possible oil horizon on what he calls the Newcastle 

 sandstone, about 175 feet above the Lakota sandstone and 50 feet 

 below the Mowry shale. In the discovery well he believes the pro- 

 iductive sand is in the Lakota sandstone about 435 feet below the 

 Newcastle sandstone. Testing for possible deeper sands had been 

 carried into the "Red beds" (Spearfish formation, Triassic?) with the 

 ntention of going still deeper. M. I. Goldman. 



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