CHAPTER IV. 



DESCRIPTIVE GEOLOGY OF THE MOSQUITO RANGE. 



Introductory. — The following pages present a detailed description of the 

 area included in the i\[osquito map, summarized from field notes made 

 during thesunmier of 1880. They contain the facts upon which have been 

 founded the general conclusions drawn el-sewhere with regard to the geol- 

 ogy of this rerrion, and therefore include many details that may not inter- 

 est the general reader, but which will be of use to those who wish to use 

 the maps on the ground or who desire to investigate critically the correct- 

 ness of the generalizations. In preparing them it has been the aim of the 

 writer to condense the description as for as could be done without omitting 

 an\- essential observations. Circumstances made the time of field work 

 extremely limited, and the detail in which it was i)Ossible to examine difi'er- 

 ent i)arts of the region was necessarily unequal. The prime object of the 

 work was to gather all information which might have bearing upon the 

 origin and manner of formation of the ore deposits of the Leadville region. 

 In the prosecution of this object nuicb information of interest in other direc- 

 tions has been collected, and many lines of investigation have suggested 

 themselves which it would have been a pleasure to pursue further had time 

 permitted. That such material be found incomplete is to be attributed, 

 therefore, to a want of opportunity rather than of scientific zeal. 



In the following description the region has been treated in the general, 

 topographical order in which it was examined; that is, following the east- 

 ern slopes of the range from the northern edge of the map southward to 

 Weston's pass, and then along the west side in the inverse direction. Both 

 geological and topographical structures lend themselves to this method of 



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