RECENT CHANGES. :} 1 .J 



limited area, tlinuiiili narrow iissures, from some deep-seated souree, cer- 

 tainly present, in their scientitic aspects, most iiiterestin<i;' ju-oblems to the 

 geologist. 



Recent Changes.— Followiug tlie oxidatiou of tlu' sulphides aiul in some 

 degi'ee associated with it, came the partial rean-angemeiit of the oxidized 

 material under the inflneiice of percolating surface water, hi some instances 

 removing the ore from iian-ow passageways and fissures and sweeping it 

 into larger receptacles, where, together with ore already deposited, it was 

 piled up on the limestone floors This rearrangement of the oxidized 

 material, seen upon opening several chambers on Ruby Hill in the course 

 of mining exploration, appeared so self-evident that no other theory of their 

 formation seems adequate to account for all the" observed facts. Such ore 

 receptacles, although more frequent near the surface, were opened at differ- 

 ent depths, but usually along lines that gave every appearance of having 

 been ancient water courses. On opening a chamber the tops of the ore 

 piles would be found covered by an accumulation of dust, fine sand, and 

 material foreign to the ore body. The stratification of material shown in 

 cross section and the settling of the heavier particles under the action of 

 water were too convincing to admit of any other mode of formation. Many 

 of the pipes coming down from the surface would be found wholly barren 

 of ore, yet carrying fragments of limestone rounded and woni smooth by 

 he action of percolating subterranean waters charged with carbonic acid. 

 Such recent di'ainage channels and pipes are by no means restricted to 

 Ruby Hill, but occur equally well preserved on Prospect Mountain, and 

 may be seen with more or less distinctness in some of the tunnels cutting 

 the ridge. They are well shown in both the Eureka and Prospect ]\Ioim- 

 tain tunnels and are so large as to serve the purposes of ventilation, and 

 in one instance, at least, so straight as to admit light from the surface. 

 Many of the tunnels suggest the existence of subten-anean water courses 

 at a time when the country was less arid than at present. 



Dr. J. S. Newbeny^ has cleverly suggested that climatic changes, with 

 alternating wet and ch-y periods, within Quaternary time in the Great Basin, 

 mav have had much to do in determining water levels in deep mines. If 



' School of Mines Quarterly, March, 1880. 



