. Transactions . ell preserved, and stains of dendriticmanganese are frequently observed. Both above and below the ore-body, the felsite is marked by an absence of iron pyrites. Thesecharacteristics obtain, as far as I have observed, on Fryer Hill,Yankee Hill, and Iron Hill, and from what I learn from others, onCarbonate Hill also. The character of the felsite throughout thedistrict appears uniform. Its contents of silica vary from 68 to 75per cent., and besides small quantities of ferric oxide, and 1 to 2 pereent. of lime, manganese, soda, and potash, the rock contains mainlyalumina. The youn
. Transactions . ell preserved, and stains of dendriticmanganese are frequently observed. Both above and below the ore-body, the felsite is marked by an absence of iron pyrites. Thesecharacteristics obtain, as far as I have observed, on Fryer Hill,Yankee Hill, and Iron Hill, and from what I learn from others, onCarbonate Hill also. The character of the felsite throughout thedistrict appears uniform. Its contents of silica vary from 68 to 75per cent., and besides small quantities of ferric oxide, and 1 to 2 pereent. of lime, manganese, soda, and potash, the rock contains mainlyalumina. The younger, intrusive, dike-porphyry (gray porphyry ofEmmons) appears more decomposed than the felsite. It is charac-terized by its mottled appearance (whence the local name, mottledporphyry), due to the separation of felspar crystals, which, on NOTES ON THE LEADVILLE ORE-DEPOSITS. £81 Fryer Hill, often attain a length of from one-half to three-quartersof an inch. The dike-porphyry, near the ore, shows kaolinization, o. :•••■:*• :-t>-^~- >..-,^>.■>.••..^• •. > ;. .. UJ^
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
