CONTENTS. XXI 



Page. 

 Other groups of mines — Contiuued. 



Mines and prospects outside the Leadville district — Continued. 



Crest of the Mosquito range 531 



London mine 532 



Peerless mine 533 



Western slopes of Mosquito range — El Capitan miue 534 



Ten-Mile district 537 



Deposits in the Archeau 538 



Chapter VI. 



Genesis of Leadville deposits 539 



Manner of occurrence — Why in Blue Limestone rather than in any other formation 540 



Composition of ores 543 



Carbonate ores 543 



Chloride ores 548 



Basic ferric sulphates 549 



Processes of alteration 550 



Agents of alteration 552 



Relative richness of galena and cerussite 553 



Outcrop deposits richer than those in depth , ■ 554 



Composition of vein materials 556 



Vein materials in general 557 



Kaolin and Chinese talc 560 



Lime and magnesia salts — Barite 561 



Manganese 562 



Ores deposited as sulphides 562 



Mode of formation 565 



Indirect evidence 566 



Negative evidence 567 



Origid or source of the metallic minerals 569 



Ascension or lateral secretion 5C9 



Source of metals 571 



Metallic contents of country rocks 574 



Baryta determinations — Lead determinations 577 



Silver and gold determinations 579 



Possible contents of porphyry bodies 582 



Appendix B, by W. F. IIillebrand. 

 CHEMISTRY. 



Tables of analyses and notes on methods employed 589 



Eruptive rocks 589 



Table I. Complete analyses 589 



Table II. Silica and alkali determinations 590 



Table III. Lead, zinc, cobalt, and barium determinations 591 



Remarks on preceding tables 591 



Table IV. Gold and silver determinations 594 



Limestones - 596 



Table V. Complete analyses of dolomitic limestones 596 



Table VI. Lime, magnesia, and chlorine determinations 598 



Table VII. Serpentine and amphibole from dolomitic limestones 598 



Ores and vein materials 599 



Table VIIL Sand carbonates 599 



Table IX. Chlorobromo-iodides of silver (iOO 



