Vol. 4] Lawson. — The Robinson Mining District. 



291 



F. S. Schmidt. The contours were sketched with the aid of as 

 many control points, established by transit and stadia survey, 

 as could be obtained in a somewhat limited time. The survey 

 plats of the numerous mining locations and traverses of the 

 roads constitute the chief frame work of the map. The altitudes 

 are approximate only, the nearest reliable bench mark being at 

 Eureka, some eighty-odd miles distant by wagon road, and the 

 only check to this being by aneroid. In relief the district has 

 a hypsometric range of about 1,600 feet, the extremes of alti- 

 tude being 6,440 and 8,040 at the east end of the district. For 

 topographic details reference must be made to the map. For 

 the purpose of locating observations the mining claims named 

 upon the map will be freely used. The field was geologically 

 surveyed and the map constructed primarily for the purpose of 

 studying the conditions of occurrence of the copper ores, and 

 of delimiting the copper bearing formation. Attention in the 

 field being thus focussed upon a special problem, many phases 

 of the general geology received but incidental or hurried study ; 

 it thus happens that, in the attempt to compile the observations 

 into a consistent account of the geology, some questions have 

 arisen for the answer to which the data at hand are insufficient. 

 Notwithstanding this, the study has been sufficiently instructive 

 to the writer to warrant his thus attempting to set forth the 

 results obtained as a contribution to the geology of Nevada and 

 to the problem of the genesis of copper ores. 



The literature of the Egan Range is rather scant. In the 

 Report of the Geological Exploration of the 40th Parallel, Vol. 

 II, pp. 486-489, is a brief note by Emmons on the general fea- 

 tures of the range based on observations made at its northern 

 end. In Bulletin 208 of the United States Geological Survey, 

 pp. 47-54, Spurr gives a somewhat more extended note on the 

 geology of the range. The only reference to the Robinson Min- 

 ing district, however, is a paragraph in the Avork just referred 

 to in which Spurr says : "At Mineral City, just west of Ely, 

 lead, silver, and gold, with some copper, are obtained. At this 

 locality a number of siliceoiis dykes cut up through the lime- 

 stone, and seem to be connected with the mineralization. In the 

 neighborhood of Ely there are considerable ore deposits." 



