PREFACE. JX 



joined the Survey as volunteer assistant, was intrusted the final petro- 

 graphical determination of all the crystalline rocks of the region, and the 

 great value of his subsequent investigations in the field of petrography and 

 mineralogy have fully justified the confidence thus placed in his ability. 



In the autumn of 1880 the corps was increased by the addition of Mr. 

 W. F. Hillebrand, who had already distinguished himself by his original 

 investigations in inorganic chemistry in the laboratory of Professor Bunsen 

 at Heidelberg; under his direction a laboratory was prepared at Denver in 

 connection with the headquarter offices of this division of the Survey. 



During the summer I was fortunate enough to secure the services of 

 Mr. Antony Guyard, a former pupil of the Ecole des Mines, and for twelve 

 years chemist at the well known metallurgical works of Johnson & Mattey, 

 London. At my request Mr. Guyard undertook the labor of making a 

 chemical investigation of the processes of lead smelting as conducted at 

 the various Leadville smelters. His sudden death at Paris, which was 

 closely followed by that of his brother Stanislas, the distinguished French 

 Orientalist, prevented the personal revision of his report which I could have 

 desired him to make; and in that which was made by Mr. Hillebrand and 

 myself we have not always felt justified in making modifications which 

 might have been judged advisable could we have discussed the points with 

 the author himself. Beyond the correction of a few clerical errors it is pre- 

 sented substantially in the form in which it was left by him. 



In November, 1880, Messrs. Hillebrand and Guyard commenced their 

 respective chemical investigations, the one of the rocks and ores, the other 

 of the furnace products of Leadville, in the laboratory at Denver. 



Mr. W. H. Leffingwell, with the assistance of Mr. Jacob, completed the 

 Leadville map during the latter part of 1880 by the accurate location of 

 various shafts and tunnels, to the number of nearly a thousand, found 

 necessary for the determination of the geological outlines, an extremely 

 laborious undertaking, carried on as it was at times with 15 to 20 feet of 

 snow on the ground. 



About the same time the topography and underground workings of the 

 maps of Iron, Carbonate, and Fryer Hills were prepared under my direc- 



