Office of the U. S. Geological Exploeation 



of the foktieth parallel. 

 GrENEEAL: Ou Marcli 21, 1867, I had tlie honor of receiving your letter 

 appointing me Geologist in Charge of the Geological Exploration of the 

 Fortieth Parallel, and defining my duties. I was therein directed to investi- 

 gate the mining regions adjacent to the 40th parallel. 



With a view most completely to accomplish this work, I detailed the 

 first geological assistant of my corps, Mr. James D. Hague, instructing him 

 to devote his time to the study of the engineering and economy of those 

 mining districts iji Nevada and Colorado which afford the most instructive 

 results, and produce the largest yield of the precious metals. 



Mr. Hague brought to this grave task education and an ample practical 

 experience. In my belief he has achieved a thorough -survey of his subject, 

 and upon the title page of the volume herewith submitted, I have given 

 his name its merited prominence. 



Assistant Arnold Hague adds a paper on the "Chemistry of the Washoe 



Silver Process," and one on the ''Geology of the White Pine Mining District." 



Assistant S. F. Emmons presents an account of the "Geology of the 



Toyabe Range," a region well known as containing the silver districts of 



Reese River. 



"The Geological Distribution of Mining Districts'," "The Comstock 

 Lode," and the "Green River Coal Basin," are the subjects upon which I 

 myself have been able to contribute chapters. 



In transmitting the present or Volume III on Mining Industry, permit 

 me to express the hope that it may realize your expectation and be thought 

 to deserve the generous facilities you have placed at our command. 

 I am. General, very respectfully, your obedient servant, 



CLARENCE KING, 



Geologist in Charge. 

 Major General A. A. Humphreys, 



Commanding Corps of Engineeis, 



Washington^ D. C. 



