P K E F ^ O E 



The field work for this report was begun in April, 1 880, and concluded 

 in March, 1881. In the spring of 1880 the Census of the Mineral Indus- 

 tries West of the Rocky Mountains was placed in my charge in addition to 

 my duties as geologist, and occupied much of my time both during the 

 period' of field work in the Washoe District and since. 



My assistants were as follows: Dr. Carl Barus, physicist, who was 

 invited at my request to join the Survey for the express purpose of resum- 

 ing the question of the electrical activity of ore bodies, a subject in which 

 I had long felt an interest. He also made experiments on kaolinization, 

 and the two chapters in this volume devoted to these subjects sufficiently 

 attest how ably he has conducted the investigations to which he was 

 assigned. Mr. F. R. Reade, assistant geologist, made a large portion of the 

 collections, which embrace nearly three thousand numbers, and, with Dr. 

 Barus, carried out many of the computations involved in the discussion ot 

 the increment of heat. I also contracted with Mr. R. H. Stretch to assist 

 me in mapping the underground geology. Mr. Stretch was for some years 

 one of the official surveyors of the Comstock, and iiis familiarity with the 

 old and inaccessible workings was of much assistance. In preparing the 

 sections it was necessary in many cases to infer the structure of localities to 

 which there was no approach from that shown in galleries on other planes, 

 a difficult task in which Mr. Stretch's aid was also very valuable. I visited 

 almost every foot of open ground, and the structural and lithological geology, 

 as well as the conjectural portions of the sections, are my own. Mr. Stretch 

 was very zealous in the collection of the specimens necessary to prove the 

 lithology of the sections, and forwarded the work of the Survey in every 

 way in his power. 



(V) 



