TEEATMEiTT OF THE COMSTOCK ORES. 253 



of material is finally collected in dams or reservoirs for still further treatment. 

 Reservoirs for this purpose are placed at convenient points along the courses 

 of the streams, or canons, on which the mills are usually placed, though on 

 account of the limited space in the narrow valleys they are necessarily small ; 

 but at the mouths of the canons, in the level country adjacent to the foot-hills, 

 there are a number of reservoirs of large capacity, in which everything brought 

 down by the streams finds a resting place, and is reserved for work in the 

 tailing mills established there. 



A few paragraphs will here be devoted to a brief notice of the character 

 of the slimes and the methods by which they are worked, the common means 

 of concentrating tailings, and the disposition of the concentrations; and, finally, 

 the treatment of the unconcentrated or ''raw tailings." 



It has already been shown that the quantity of slimes produced in crush- 

 ing ore varies considerably in difierent mills. In some mills the proportion 

 of slimes is thought to be about two per cent, of the ore crushed by the 

 stamps, while in others it is said to be as high as ten per cent. This is partly 

 due to the difference in the character of the ore or its gangue, and partly to 

 the difierence in the conditions under which the crushing takes place. 



As these slimes carry with them much of the very finely crushed silver 

 ore, their assay value is not only considerably higher than that of common tail- 

 ings, but is often higher than that of the original ore. Especially that portion 

 of the silver-bearing mineral of the ore which exists in the form of rich 

 sulphurets, being soft and readily crushed, is liable to be reduced to 

 an impalpably fine condition, particularly if freed from particles of quartz, 

 that might, if present, preserve it in a coarser form, and escape with it from 

 the battery before being reduced to slime. 



AMALaAMATiON OF Slimes IN Pans.— The attempts to work slimes by 

 ordinary methods in pans have not hitherto, or at least until recently, been 

 followed by very satisfactory results. This has been attributed partly to the 

 finely divided and clayey condition of the material itself, the particles of 

 quicksilver and amalgam becoming coated with an adhering film of the slimy 

 substance, preventing amalgamation and involving great mechanical loss of 

 quicksilver ; partly, also, to the probable existence of the silver in the form of 

 sulphurets, as just indicated — a combination resembling that of the first-class 



