abstracts: geology 523 



Hills at the boundary of Weston and Crook counties in northeastern 

 Wyoming. Of the rocks exposed the highest is about 1200 feet above 

 the base of the Upper Cretaceous Pierre shale, the lowest about 100 

 feet above the basal Upper Cretaceous Dakota sandstone. From the 

 records of nearby borings about 2830 feet of rocks beneath this, to a 

 depth of 398 feet in Mississippian limestone, are described. The 

 structure is represented by contours at 50-foot intervals and by dia- 

 grammatic cross sections. The general southwest dip of the region is 

 interrupted in the Upton and Thornton domes which lie along a com- 

 mon axis trending parallel to the general strike. Dips range from a 

 few degrees to 25 °. The Thornton dome is about 2 miles wide by 6 

 long and rises about 500 feet above the syncline which bounds it on 

 the east. The Upton dome is about 1V2 miles wide and 4 long, and 

 about 100 feet high. The only developments on these domes are two 

 dry holes apparently well located and drilled to the red beds, but a 

 number of wells are daily producing 5 to 10 barrels of high-grade light 

 oil from a sandstone immediately above the Greenhorn limestone, 

 lying 450 to 850 feet below the surface in a structural terrace about a 

 mile long and wide just beyond the northwest nose of the Thornton 

 dome, which is the more northerly of the two domes. 



M. I. Goldman. 



GEOLOGY. — The Sunset-Midway oil field, California. Part II. 

 Geochemical relations of the oil, gas and water. G. S. Rogers. 

 U. S. Geol. Survey Prof. Paper 117. Pp. 103, pis. 2, figs. 8. 

 1920. 



Part I of this paper describes the general geology of the Sunset- 

 Midway region and the development and underground conditions 

 in the productive field, and discusses also the origin and migration 

 of the oil. California petroleum differs in many important respects 

 from the varieties produced in other parts of the United States, and a 

 considerable amount of chemical study has been devoted to it. Part 

 II describes the chemical and physical properties of the California 

 oil and gas, and discusses the relations of these properties to the geologic 

 occurrence, emphasizing especially the importance of the chemical 

 action of mineralized water as a cause of variation in gravity of the 

 oil and the formation of carbon dioxide in the gas. The paper includes 

 also some figures on the geothermal gradient, and a discussion of the 

 occurrence and nature of oil-field waters and their invasion of oil sands. 



J. D. Sears. 



