512 DESCRIPTIVE GEOLOGY. 



the groundmass reveals no new constituents, but a purely sphaerulitic 

 structure, a detailed description of which will be found in Professor Zirkel's 

 •report, showing- in an interesting manner a close analogy existing between 

 these rocks and the Tertiary rhyolites. And yet while this microscopical 

 analysis presents much that suggests such a comparison, no practiced field- 

 lithologist would ever mistake it for a late eruptive rock. 



This region of Spruce Mountain forms a mining district, which, if not 

 of great economic importance, possesses much that is of interest from a 

 geological point of view, and worthy of detailed study. As the limestones 

 have undergone considerable displacement and fracture, dependent upon the 

 intrusion of crystalline rocks, so, in like manner, most of the ore-deposits 

 show an intimate connection with both formations, usually occurring in the 

 former, in close proximity with the latter. In places, they are found in 

 seams and irregular breaks in the beds ; at others, lying between the strata, 

 and again as contact bodies between limestone and porphyry. All the ores 

 would appear to be secondary products, such as carbonates and sulphates 

 derived from the decomposition of galena and related minerals. Galena, 

 although found in small masses, is not abundant ; wulfenite occurs in small 

 quantities. 



Little Cedar Mountains.— This group of mountains lies midway 

 between the Peoquop and Humboldt Ranges, and may be considered as a 

 continuation southward of the Fountain Head Hills, connected by Cedar 

 Pass. They rise abruptly above the valleys, and form but a small group 

 nearly 12 miles in length by about 10 in width; the highest summits attaining 

 an altitude of between 2,000 and 2,500 feet above the valley. Albion 

 Peak, the culminating point, lies 8,391 feet above sea-level. The summits 

 and higher slopes are well covered by a fair growth of coniferous trees, 

 but the mountain mass is exceedingly dry, no stream being known, and 

 probably not even a running spring. 



But little opportunity was afforded for its geological study with any 

 detail, and only the main features were gathered. Enough, however, was 

 seen to recognize that the same geological horizons that are developed along 

 the northern end of the Gosi-Ute and Peoquop Ranges re-appear here with 

 the same characteristic structural and lithological behavior; that is, the 



