Washington, D. C, May 15, 1875. 



Sir : I have the honor herewith to submit my report for 1874. 

 According to instructions received, I took the field July 14, 1874, as 

 geologist of the San Juan division, and returned with it to Denver, 

 Colo., October 19, 1874. During that time more than 3,000 square miles 

 were surveyed topographically and geologically, including all that sec- 

 tion of country known as the San Juan mining district. The very 

 rugged character of the region, and the inclemency of the weather, 

 impeded our progress somewhat, and the latter not unfrequently was a 

 serious obstacle to the successful and speedy completion of the work. 



Four chapters and a " conclusion " comprise the accompanying report. 

 Some difficulty was experienced in finding a suitable basis for classifica- 

 tion in arranging the material collected. The plan of dividing by 

 formations was adopted finally. The first chapter treats of the rneta- 

 rnorphic area, the second of the volcanic, the third of the sedimentary 

 area. In the fourth chapter the geology and geognosy of the imme- 

 diate vicinity of the mining region, as well as the mineralogical features 

 of the mines, have been considered. A circumstance that will let this 

 latter chapter perhaps appear somewhat unsatisfactory lay in the fact 

 that the lodes discovered and claimed had in but very few instances 

 been worked to any greater extent than was required by law to hold 

 a good title. It was impossible, therefore, to study anything, save the 

 surface characteristics. I beg leave to submit this chapter merely as a 

 preliminary one, hoping to be able, at some future time, to make inves- 

 tigations upon the same subject when all conditions may be more favor- 

 able. 



I wish here to express my thanks to Mr. A. D. Wilson, chief topog- 

 rapher of the San Juan division, and to Mr. F. Rhoda, his assistant, 

 for their uniform kindness and courtesy during the field-season and in 

 the office. 



To Prof. F. B. Meek I am under obligations for the identification of 

 fossils. 



Hoping that this report may meet your requirements, I have the 

 honor to remain your obedient servant, 



FREDERIC M. ENDLICH. 



Dr. F. V. Hayden, 



Geologist in Charge, U. 8. Geological and 



Geographical Survey of the Territories. 



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