TABLES OF ANALYSES AND NOTES ON METHODS EMPLOYED. 

 ERUPTIVE ROCKS. 



Table I. — Comphtc analyses of eruptive rocks and constituent minerals. 



[The Coll. Ko. is the number given to the specimen in the collection of Leadville rocks deposited in the Nati< 

 Moseam.j 



/A little Mi;0 present. 



<7TVator and alkalies not tested for. 



TiBy ignition ; want of material prevented a second de- 



lermmation. 



aVery little Fe203 present; FeO uot determined. 



frlncludes traces of Fe203. 



cincludes any Fe^Os present. 



dCalculated from the FejOs found. 



cMnOa. 



1. "White Porphyry. Coll. No. 27p. Quarry in California Gulch, southwest slope of Iron Hill, near Leadville. Com- 

 posed chiefly of quartz orthoclase, and plagioclase ; no biotite or hornblende ; little magnetite; no apatite; feldspars attacked; 

 muscovite and calcito secondary. 



2. Muscovite crystals iVoni White Porphyry. Sheet on south slope of Little Zion. Analysis only approximate, 

 being made to prove the mica to be muscovite. 



3. Mount Zion Porphyry. From Little Harry shaft, Prospect Mountain. 



4. Lincoln Porphyry. Coll. No. 75. Summit of Mount Lincoln, Park County. Rock nearly fresh; contains quartz, 

 orthoclaso (large crystals), "plagioclase, biotite ; biotito partly changed to chlorite, containing rutiJe <?) needles ; some mag- 

 netite and apatite ; calcite. 



5. Gray Porphyry. Coll. No. 59a. NeavOnota claim, Johnson Gulch, Leadville. Rock nearly fresh ; contains quartz' 

 orthoclase (large crystals), plagiochise, and biotite. Details same as for 4. 



6. Largo pink crvstats of feldspar from Gray Porphyry (No. 5). Coll. No. 59a. 



7. Porpbyrito. Coll. No. 12G (Type V of table, see Appendix A). Near the Northern Liglit mine, Lower Buckskin 

 gulch, Park County; intrusive sheet. Contains abundant plagioclase and hornblende, and little biotite; quartz and ortho* 

 clase (?) in groundinass. Magnetite and little apatite. 



8. Porphyrite. Coll. No. 2G0. Typo VI of table (see Appendix A). Head of North Fork of Mosquito gulch, Park 

 County. Dike in Archean. Fresh. Much biotite and plagioclase; some quartz in grouudmasa. Very little hornblende, 

 magnetite, pvrite, apatite. 



9. Nevadite. Coll. No. 397. Northeast point of Chalk Mountain, Ten-Mile district. Contains sanidine, plagioclase, 

 and quartz in abundance; little biotito and magnetite. 



10. Sanidine from Nevadite. Coll. No. 136. Southern edge of Chalk Mountain. 



11. H\-persthene-ande8ite. Coll. No. 144. Buffalo Peaks, Park County. Very fresh. Plagioclase and hypersthene 

 abundant; considerable augite, magnetite, apatite; glass base. 



12. Hyporsthene from hyperstheneandesite. Coll. No. 144 (see 11). The hypersthene forthis and the two following 

 analyses was separated from tlie other constituents of the rock by hydrofluoric acid, as recommended by Fouqu6 in San- 

 torin et ses 6ruptions. 



IS, Same as 12, but of a different sample. 



14. Hypersthene from hvpersthene-andesite. Coll. No. 150. Buffalo Peaks, Park County. Particles of undecom- 

 post-d feldspar were visible lUtached to the crystals and fragments of hypeisthene analyzed. 



