APPENDIX. 



MJI^ERALOGICAL JS^OTES AND A CATALOGUE OF THE MIN- 

 ERALS OF COLORADO TERRITORY. 



MINEEALOGICAL NOTES. 



One of the most interesting regions in Colorado, from a mineralogical 

 point of view, is undoubtedly the vicinity of Gold Hill, of which Mr. 

 Marvine treats in his report, as it is located within his district. 



There a number of dikes of porphyry have found their way out through, 

 the granite, and, contact between the two, a number of lodes have been 

 found, several of which have attained considerable celebrity. The Red 

 Cloud and Cold Spring are located on the two sides of a porphyry-dike 

 50 feet in thickness, striking about northeast to southwest, and from 

 them principally the rare and valuable tellurids, sought for by mineral- 

 ogists, have chiefly been obtained. Prof. F. L. Schirmer, of Denver, 

 had the kindness to supply me with a number of specimens from the 

 Red Cloud mine, which I have examined, and herewith give a report 

 upon. Before speaking more i>articularly of the tellurids, a few words 

 may be said explanatory of the circumstances under which they are asso- 

 ciated with other minerals at the mines of that locality. 



Composing the dike between the Red Cloud and Cold Spring, we find 

 a porphyry of dark-grayish to purplish color, containing numerous small 

 crystals of two varieties of feldspar in its cry ptocry stall ine, compact 

 paste. While forming the hanging- wall of the Red Cloud, it is the foot- 

 wall of the vein opposite. Fragments of this porphyry, mixed with par- 

 ticles and streaks of quartz and feldspar, together with small flakes of 

 talc, make up the gangue-rock of the Red Cloud, collecting in small 

 cavities, crystallizing in cubes combined with the pentagonal dodeca- 

 hedron. Pyrite occurs throughout the vein, also forming at times nar- 

 row streaks, but invariably with a strong tendency to crystallize. At 

 some points the porphyry too is thoroughly impregnated with this min- 

 eral. Galenite occurs sparingly in cubical crystals ; also sphalerite in 

 narrow seams. Quartz-crystals, coated by ferric oxide, are found in the 

 small cavities occurring with them, both of more recent origin than the 

 sulpliurets. Compounds of silver, copper, selenium, &c., with sulphur, 

 seem to be wanting entirely 5 instead, however, we have the unusually 

 rich occurrence of tellurets, of whicliwe shall speak presently. 



To the west of the Red Cloud is the Cold Spring, the ores of which 

 sbow no variation, however, while the same granite and the same por- 

 phyry form its walls. 



East of the Red Cloud, striking almost due east and west, is the Wi- 

 nona, located between two walls of gneiss. In this lode the gangue- 

 rock is mainly quartzitic, containing small portions of decomposing 

 feldspar and of talc. - Chalcopyrite and pyrite form the main ore, occur- 

 ring in streaks and thin threads partly, partly disseminated in crystals 

 of cubical and dodecahedral form throughout the gangue. 



