VIII GEOLOGY A]!fD MINING INDUSTRY OF LEADVILLE. 



it possible to carry on the chemical investigations that form one of its most 

 important and essential features. The first want was accurate and detailed 

 topographical maps, which are more than usually indispensable in the 

 vicinity of Leadville, where the entire rock surface is covered by debris, and 

 the geological structure had to be reconstructed by gathering into a con- 

 nected whole the data derived from thousands of isolated shafts and tunnels 

 which had penetrated below the surface accumulations. 



This want was supplied by Chief Topographer A. D. Wilson, the une- 

 qualed accuracy and rapidity of whose work can only be adequately appre- 

 ciated by those who have had occasion, as we had, to put it to the test of 

 actual instrumental verification. The field work of the map of Leadville and 

 vicinity was completed by him and his two assistants during the months 'of 

 August and September, 1879, and that of the map of Mosquito Range during 

 part of July, August, and September, 1880. 



In December, 1879, 1 commenced the study of the ore deposits of Lead- 

 ville. In this I received most invaluable aid from Mr. Ernest Jacob, grad- 

 uate of the Royal School of Mines of London, who, working at first as 

 volunteer, rendered most continuous and unwearied service during the whole 

 continuance of the investigation To his keen insight into the intricacies 

 of geological structure, his untiring energy in exploring every accessible 

 prospect-hole in the region, and his accurate appi-eciation of the bearing 

 of the data thus gathered, is attributable in great measure tlie successful 

 unraveling of the complicated problem presented in the region represented 

 on the map of Leadville and vicinity. So complicated a region, I make 

 bold to say, it rarely falls to the lot of a geologist to study in detail. 



In July, 1880, it was first practicable to undertake the study of the 

 high mountain region represented on the map of the Mosquito Range. 

 Here geological and topographical field work went hand in hand, and my 

 party worked together with that of Mr. Wilson until heavy snows at the 

 end of September put an end to outside work. In this field work I had 

 the assistance of Mr. Whitman Cross, who had made a special study of 

 microscopical petrography under Professor Zirkel, of Leipzig, and of Prof 

 Arthur Lakes, of the School of Mines at Golden, Colo., who devoted his 

 summer vacation to this work. To Mr. Cross, who, like Mr. Jacob, first 



