78 abstracts: geology 



GEOLOGY. — Molybdenite and nickel ore in San Diego County, Cali- 

 fornia. F. C. Calkins. U. S. Geological Survey Bulletin 640-D. 

 Pp. 73-82. 1916. 



Molybdenite has been reported to occur at several places in San 

 Diego County. The deposit near Ramona, which has attracted most 

 attention, was visited in December, 1915. The molybdenite at this 

 locality is unevenly disseminated in an aplite dike which cuts granite, 

 the principal rock of the region. The deposit has not been shown to 

 have commercial value, though further development and prospecting 

 seem to be warranted. 



A nickel prospect, the Friday mine, near Julian, was also visited. 

 The nickeliferous deposit, which has been explored to a depth of 200 

 or 300 feet, lies at an irregular contact between mica schist and gabbro. 

 It consists mainly of pyrrhotite, but contains pyrite, chalcopyrite, and 

 an iron-nickel sulphide, probably polydymite. Both in constitution 

 and mode of occurrence it resembles the Sudbury deposits and is pre- 

 sumably similar in origin. The sulphides are high enough in nickel 

 to constitute ore, provided a fairly large body of them can be uncovered. 



F. C. C. 



GEOLOGY.- — Gypsum in the southern part of the Bighorn Mountains, 



Wyoming. Charles T. Lupton and D. Dale Condit. U. S. 



Geological Survey Bulletin 640-H. Pp. 139-157, with 3 plates. 



1916. 



Gypsum has been known to occur in a belt of rocks surrounding the 



Bighorn and Owl Creek mountains, Wyoming, from the early days of 



exploration. The amount of this material at several places is great, 



but owing to the slight demand for it little attention has been given to 



its utilization until the last few years. 



The gypsum occurs at two horizons — the upper at or near the top of 

 the Chugwater formation, or Red Beds, and the other in the upper 

 part of the Embar formation. Only the upper bed, however, is of 

 economic importance at Sheep Mountain and in the vicinity of 

 Thermopolis. 



The rocks exposed in the region described in this report range in age 

 from pre-Cambrian to Quaternary. The Embar and Chugwater 

 formations, winch contain the gypsum beds, are described in detail. 



R. W. S. 



