GENERAL INDEX. 



415 



Contact, permanent position of, on 400-foot level of the 



Richmond mine 337 



position of, on 500-foot level of Kich- 



moud mine 334 



position of, on 600-foot level of Rich- 

 mond mine 344 



position of, on surface of Richmond 



mine - 51 



temporary 317 



Contact bag, description of 324 



Contacts, metallic (plates and gada), objectionable 358 



Cooling, influence of, on precipit^ation 226 



Cornwall, electrical activity of ore bodies in 310, 311, 312 



Cortez Peat, propylite from 142 



Range, foothills of, propylite from 140 



Councler, C, analysis by table following 151 



Country rock attacked by acids 226 



Cross-spur below graveyard, analysis of earlier hom- 

 blende-andesite from . . . 

 table following page 151 



propylite from 142 



Cross-spur quarry (D. 2), analysis of later homblende-an- 



desitefrom table following page 151 



Crown PointRavine(B.4),angite-aude8ite from. 87,126,128,151 

 earlier hornblende -and esite from . .87, 125 



epidote from 213 



propylite from 86, 87, 135, 136, 137 



Crushing action, effects of 394 



Curtis, J. S., assays of rocks by 155, 223 



Dayton, subaqueous eruptions near 14 



Decomposition. {See illustrations.) 



areaof..... 72,238,383 



due to solfataric action 240 



evidence of an external cause for the. . . 239 



of blocks of rock 79 



of minerals. (See each mineral.) 



of the rocks 72, 209, 369 



(5eelithologicaldescriptionofeachrock.) 



rocks affect ed by , 239 



Devil's Gate (D. 6), metamorphic diorite near 108 



Dowey, F. P., analysis by 154 



on the feldspars of the later homblende- 



andesite 68 



Diabaee, assays of 154, 155 



earlier. (See illustrations.) 



analysis of table following 151 



description of slides of 112 



feldspars of 



horublendic 52 



laminated 51 



litbological description of 48 



occurrence and age '....197, 374,381 



relations to the Lode 197 



silica contents of 152 



later. (See Black Dike.) 



description of slides of 116 



litbological description of 52 



occurrence and age of 198, 381 



silica contents of 152 



of Ophir Ravine, possibly a diorite 36 



of Orange Mountain, 'N.J 53 



selected for experiments on kaolinization 236 



silver traced to 224 



the possible source of ore 222 



Diorite, assays of 154, 155 



Page. 



Diorite, eruptive 378 



(See illuBtrations.) 



brecciated 41 



containing tourmaline 97 



dark varieties 38 



feldspars of 406 



granular, analysis of table following 



page 151 



granular, description of slides of 93 



hypothesis concerning 194 



litbological character of 34 



micaceous, analysis of table follow- 

 ing page 151 

 micaceous, occurrence in the Tellow 



Jacket 277 



micaceous, porphyritlc, description of 



slides of 104 



occurrence and age 192, 381 



porpbyritic 39 



porphyritlc, analysis of . . -table follow- 

 ing page 151 

 porphyritlc, description of slides of .. 97 



porpbyritic, laminated 41 



porphyritlc, silica contents of 152 



possibility of metamorphic origin 195 



relations of varieties of 42, 193 



metamorphic, analysis of table following page 151 



brecciated 43 



descriptions of slides of 106 



feldspars of 406 



litbological character of 43 



occurrence and age 195 



relations to quartz-porphyry 43 



Zirkelon 12 



Dflelter, C, on propylite 90 



Drill-holes, disposition of 325 



without specific electrical effect 360 



Dutton, C. E., on propylite 81 



Earth- currents, intensities of 346 



discrepancies produced by 360 



Earth potential, constancy of 352 



graphic representation of 342, 348, 354, 



^ 362. 366 



how measured 320, 327, 328, 352 



maximal values of 317 



observed at the Richmond mine . . . 340, 347, 

 350, 351, 355 



series of values of 329 



values of on 400 and 500-foot levels of 



the Richmond mine 342 



values on 600-foot level of the Richmond 



mine 349 



variation of, on the surface 351 



variation of, with distance 342, 348, 352 



East vein, a result of faulting 182 



inferences from the 271 



Eckart, 'U'. R., mining machinery of the Comstock 1 



Eldorado cropi)ings, analysis of diorite from the table 



following page 151 



diorite dike near the 40, 42, 104 



Electric survey across an ore body 344 



over the surface 351 



through an ore body (Eureka) 332 



Electrical action, confined to particular parts of the ore 

 body 351,364 



