RECENT CHANGES. 315 



limited area, through narrow fissures, from some deep-seated source, cer- 

 tainly present, in their scientific aspects, most interesting problems to the 

 geologist. 



Recent changes. Following the oxidation of the sulphides and in some 

 degree associated with it, came the partial rearrangement of the oxidized 

 material under the influence of percolating surface water, in some instances 

 removing the ore from narrow 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 worn smooth by 

 he action of percolating subterranean waters charged with carbonic acid. 

 Such recent drainage 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 Moun- 

 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 subterranean water courses 

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



Dr. J. S. Newberry 1 has cleverly suggested that climatic changes, with 

 alternating wet and dry periods, within Quatemary time in the Great Basin, 

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



1 School of Mines Quarterly, March. 1880. 



