1881.] 4*^ [Konig. 



tains in astonishing abundance. They are easilj^ traced on the bald slopes, 

 which rise from one to three thousand feet above timber line. The 

 geology, as already stated, is quite simple. Orthoclastic eruptive rocks — 

 Quartz-porphyry, Porphyrite and Trachyte^ — overlie granitoid metamor- 

 phic schists (chiefly gneiss) as an enormous sheet one mile thick. Only 

 towards the West we find palgeozoic rocks, sandstones, limestone and 

 coal beds, lying between the crj^stalline top and bottom rocks, not exceed- 

 ing probably 500 feet in thickness. All the peaks and crests visited by me 

 were found to be made up of porphyritic rocks, schists and sedimentarj- 

 rock being only found in the deep canons. The silver bearing veins I 

 found to be confined to the eruptive rocks with but few exceptions, i. e., 

 the "mineral farm," near Ouray in Silurian limestone; the "black 

 Wonder mine" and some other veins in Burough's Park, which lie in 

 granitoid gneiss.. 



One of the most interesting sections of this wonderful region is Pough- 

 Jceepsie Gulch, one of the head forks of the Uncompaghre river. Here we 

 find numerous veins in a bleak wilderness directly under the pass which 

 leads from the Uncompaghre valley over into the Cement creek, one of the 

 feeders of the Animas river. Very prominent among its neighbors is the 

 Alaska vein which was opened by two adits at the time of my visit last 

 August. The vein is well defined, striking nearly north and south, with 

 almost vertical dip. The breast of the lower adit showed beautiful ore. 

 Nests of gray copper and Alaskaite in a gangue of quartz and barite. 

 Even with candle light the gray copper and Alaskaite (Bismuth silver ore 

 so called here) are distinguishable, and are separated by handpicking into 

 first class, and second class ore. I fotmd some difficulty in procuring 

 specimens, as the foreman had orders not to allow specimens being taken 

 away. 



Physical properties of Alaskaite. The specimens consist of a more or less 

 intimate mixture of the new mineral with barite and chalcopyrite, and 

 sometimes a little quartz. Neither blende nor galenite could be detected. 

 The small quantity of antimony shown by the analysis might be due to the 

 presence in the mixture of some gray copper or other Stibiosulphosalts, or 

 may be replacing bismuth in the Alaskaite. But could in no way interfere 

 with the correct definition of the new mineral, as Avill be seen later. The 

 complete decomposition with hydrochloric acid speaks quite in favor of the 

 latter view. 



The structure of Alaskaite is small foliated, some smooth cleavage planes 

 may be observed here and there. Its color is whitish lead-gray, approach- 

 ing bismuthinite ; its lustre strongly metallic ; opaque. Color of the fine 

 powder is bluish-gray. The structure forbids a determination of hardness, 

 but the mineral is mild in the mortar, and easily friable. 



The specific, gramty was determined with the fine powder used for the 

 Analyses C and D, and found to be 6.878 by the following calculation : 



Let S = IK .3165 = A + B + C (Alaskaite -f barite -f chalcopyrite) 



A S— B— C 

 then we have p = j = j ^ ^ 



