TABLES OF ANALYSES AND NOTES ON METHODS EMPLOYED. 

 ERUPTIVE ROOKS. 



TABLE I. ComplHe analyses of eruptive rocks and constituent minerals. 



[The Coll. No. is the number given to the specimen in the collection of Leadville rocks deposited in the Nationa 

 Museum.) 



/A little MgO present. 

 i Water and alkalies not tested fur. 

 A By ignition; want of material prevented a second do- 

 termination. 



a Very little FesCh present; FeO uot determined. 



6 Includes traces of FesOs. 



c Includes any Fe-X)3 present. 



d Calculated from the FejOs found. 



eMnOi. 



1 White Porphyry. Coll. No. 27p. Quarry in California Gulch, southwest slope of Iron Hill, near Leadvillo. 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 from White Porphyry. Sheet on south slope of Little Zion. Analysis only approximate, 

 bein<* made to prove the mica to be muscovite. 



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



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

 orthoclase (large crystals), plagioclase, biotito; biotite partly changed to chlorite, containing rutile (!) needles; some mag- 

 netite and apatite ; calcite. 



5. Gray Poiphyry. Coll. No. 59a. Ncav Onota claim, Johnson Gulch, Leadville. Rock nearly freeh ; contains quartz' 

 orthoclase (largo crystals), plagioclase, and biotit*. Details same as for 4. 



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



7 Porpbyrite Coll No. 120 (Trpe V of table, aeo Appendix A). Near the Northern Light mine, Lower Buckskin 

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

 clase '()) in groundmass. Magnetite and little apatite. 



8 Porphyrite. Coll. No. 2CO. 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 groundmass. Very little hornblende, 



9 e 'N > evaaJte. Pa c 1 oli. No. 397. Northeast point of Chalk Mountain, Ten-Mile district. Contains sanidine, plagioclase, 

 and quartz in abundance; little biotito and magnetite. 



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



11. Hypersthene-andesite. Coll. No. 144. Buffalo Peaks, Park County. Very fresh. Plagioclase and hypersthene 

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



12 Hypei8thenefromhvpertheuoanile*ite. Coll.No. 144 (see 11). The hypersthene for this and the two following 

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

 torin et BBS eruptions. 



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



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

 posed feldspar were visible attached to the crystals and fragments of hypersthene analyzed. 



