166 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



those last-mentioned localities. On Adams Hill that rock is harder, more 

 compact, and less subject to sudden changes in its physical characteristics. 

 In many places the Hamburg limestone is capped by a conglomerate con- 

 sisting of bowlders of limestone cemented together by a tough calcareous 

 material. In this conglomerate fragments and even bowlders of ore are 

 often found. This ore does not resemble in any respect the ores of Ruby 

 Hill, and it is likely that it, as well as the accompanying limestone, are the 

 products of the erosion of the immediate neighborhood, which have been 

 cemented together by calcareous waters. 



ore deposits. — The deposits of this portion of Eureka District are as varied 

 in regard to form as those of Ruby Hill, but in many other respects they 

 differ from them. There is very little resemblance between them and true 

 lodes, though they are all more or less connected with fissures and slips, 

 and some of them which occur in the limestone near the shale seem to have 

 a general course parallel to the contact of those formations. An instance 

 of this occurrence can be observed in the Bowman mine, which lies near the 

 Secret Canon shale. Caves, which are so characteristic of Prospect Mount- 

 ain and Ruby Hill, are rare; and although it is possible that such openings 

 may exist in numbers, the explorations have not yet revealed them. It is true 

 that the deepest mine workings have as yet attained but a moderate depth, 

 not much exceeding 200 feet, although the explorations have been quite 

 numerous. Nevertheless it is probable that if caves were numerous they 

 would have been revealed before now, for it can be safely said they are of more 

 frequent occurrence and usually of greater extent near the surface than at 

 great depth. This is easily explained by the fact that the waters carrying 

 carbonic acid, to which they owe their origin, becomes saturated with cal- 

 cium carbonate as it descends, thereby losing its solvent power. The 

 absence of caves, which in other portions of the district are so intimately 

 connected with ore bodies, would seem to indicate that the genesis of these 

 deposits was somewhat different from that of the ordinary class. This 

 theory is also sustained by the fact that the ores are of a different character 

 from those of Ruby Hill. The most noticeable difference is the prevalence 

 of quartz ores. This can be said to be the distinguishing feature of the 

 ores of Adams Hill, as well as those occurring in the Pogonip limestone on 



