BRIEF OUTLINE OF RESULTS. 



The economical importance of the Comstock Lode appears from the fact that in twenty-one years a little over 

 $306,000,000 worth of bullion has been extracted from it. Of this abont $132,000,000 worth was gold. The mines are the 

 deepest in America, reaching a distance of over 3,000 feet from the surface, and they contain about 185 miles of galleries. 

 Besides the scientific importance attaching to the occurrence of the immense accumulation of ore, the Lode and 

 District present other features of great interest. The nature of the rocks associated with the ores, some points of struct- 

 ure, and even the character of the deposit, have received different explanations at the hands of different observers. A 

 digest of the memoirs of Messrs. von Eichthofen, King, Zirkel, and Church forms one chapter of the volume. 



The subject of rock decomposition has received especial attention in the examination described in this report. 

 This study has led to some lithological and mineralogical observations of interest, and to the identification of all of the 

 Washoe rooks with well-established rock species. The greater part of the hanging wall of the Lode is diabase ; the "black 

 dike" is also a variety of diabase, and the supposed trachyte of the District is a hornblende-andesite. The so-called 

 propylite of Washoe comprises a number of Tertiary and pre-Tertiary rocks, reduced to a nearly uniform appe.aranco by 

 decomposition- The erroneous determination of these altered rocks as an independent species arose mainly from a confusion 

 between green and fibrous hornblende and chlorite. The supposed propylites from the other districts in the United States, 

 microscopical determinations of which have been published, were also examined and fonnd to afford no sufficient evidence 

 of an independent rock species. 



A discussion of faulting leads to an explanation of the similarity of the shape of the west wall of the Lode and the 

 form of the adjoining face of the Virginia range. The ravines of the latter are a direct result of faulting, and are only 

 slightly modified by erosion. A cross-section of the country on the Sutro Tunnel line shows that the surface forms a 

 logarithmic curve in accordance with the theory, which is further supported by experiments. The sheeted structure of the 

 country seems to be referable to fMilting and not to eruptive bedding. The theory leads to rules applicable in prospecting 

 disturbed but not greatly eroded districts. The details of the topography of grassy hills are chiefly due to landslips, which 

 come under the law of faults in a modified form, and the characteristic curves of smooth hill-slopes are logarithmic. 



The order of succession of rocks in the Washoe District is: Granite, metemorphics, granular diorite, porphyritic 

 diorite metamorphic diorite, quartz-porphyry, earlier diabase, later diabase, earlier hornblende-andesite, augite-andesite, 

 later hornblende-andesite, and basalt. Hornblende-andesite thus followed as well as preceded augitc-andesite- 



Chemical evidence is offered to show that the pyrite of the region is a result of the action of soluble sulphides on the 

 ferro-magnesian silicates of the rocks. Chlorite is held to be a product of the decomposition of hornblende, augite, or mica, 

 while epidote forms at the expense of chlorite under certain conditions, but never from feldspar. There is extremely little 

 kaolinization at Washoe, the feldspars having yielded to another kind of decomposition The diabase of the hanging wall 

 when fresh was argentiferous and auriferous, and the precious metals of the Lode are traced to this rock with much 

 probability, the lateral-secretion theory being thus affirmed. It is farther supported by the dependence of the other ore 

 bodies of the District on the character of the inclosing rock. 



The hypothesis that the heat of the Lode is due to the kaolinization of feldspar is not confirmed either by theory 

 or experiment. On the other hand, there is much geological evidence pointing to a deep-seated source of heat, probably of 

 volcanic origin. This conclusion is confirmed by extensive temperature observations, from which it appears that from the 

 surface downwards the increase of heat is uniform, about 1° F. for every 33 feet, while in a horizontal direction the heat 

 decreases in a geometrical ratio to the distance from the Lode. 



Experiments on the kaolinization of feldspathic rock, conducted at the boiling point of water iuid extending over a 

 number of weeks, show that no heating effect due to this cause conld bo detected with an apparatus delicate enough to 

 register a change of temperature of 0°.001 C. 



The numerous geological sections are discussed in Chapter VLII., and the application of the explanations suggested 

 in the preceding chapters is there shown in detail. AU the important and profitable ore bodies of the Comstock, it appears, 

 have occuned a't or close to the west face of the earlier diabase ; and it is near that surface, and there only, that exploration 

 is at all likely to be successful. The mode of occurrence of bonanzas is considered, and hopeful prognostications are made 

 for at least two portions of the LodE; but a series of bonanzas nearly on the same level, such as was found in the east 

 vein near the surface, is not likely to recur. 



Electrical surveys were made both on the Comstock and at Eureka. At Virginia only negative results were 

 obtained. At Eureka a distinct though smMl difference of potential occurs near ore bodies, and with sufficiently deUcate 

 apparatus the method might there be used for prospecting. It is believed that sulphuret ores would have given results 

 of a more convenient magnitude than the carbonate ores of Eureka. 



(XV) 



