MOUNT BISCHOFF. 355 



tating part of the material lower down the slope, and form 

 a deposit of a similar tliickness all over the lower-lying' 

 ground ? but as this is not the case, it is only reasonable to 

 accejit that the country, or better, the locality, in days gone 

 by presented a diflferent appearance from what we see at 

 present. Besides, it is next to certain that these porphyry 

 dykes were at one time of far greater height, and only 

 through atmospheric action have they been disintegrated, 

 and formed this enormous deposit of porphyry- wash from 

 top to bottom of the workings, of over 70 feet in thickness in 

 one place, as previously stated. A slaty admixture in this 

 wash is only noticeable on the north-western rising ground, 

 extending right up to the summit of the Mount ; but the 

 deposit here gets thinner as it gets nearer the top of the 

 Mount, still maintaining its stanniferous character. 



The other formation — the Brown Face — is unique in itself 

 A large ferruginous gossan formation rises about 108 feet 

 above the floor of the crescent already alluded to, and is 

 hemmed in on both sides, i.e., east and west, by porphyry 

 wash of a certain depth. At the depth of 30 feet below the 

 floor prospecting works have been carried on, and have 

 proved that the formation at this de])th is resting upon the 

 shite on the north side, but is cased in on the other sides, at 

 the points of intersection of the drives, by a thick coating of 

 iron pyrites and black clay, the latter separating the former 

 from the gossan formation of the Brown Face. It is only 

 reasonable to suppose that this formation, i.e., the black clay, 

 continues to a greater depth, and must act as a protecting 

 mantle of the other. 



Different theories have been formulated to explain the 

 origin of the Brown Face, but up to the jiresent the prol)lem 

 is unsolved. By all appearances it is not a lode; but whether 

 it is a " stockwerk " or a " geyser deposit," as some assert, I 

 will not venture to say at present ; the last idea seems to me, 

 however, quite out of the question. I am rather of opinion 

 that it was originally a huge iron pyrites formation, impreg- 

 nated with tin ore, the same as represented in the North 

 Valley Lode, and that, through the action of air and water, 

 and other agencies oi' nature's laboratory at present not 

 noticeable, the enormous change in the mineral character and 

 outward appearance has been brought about. This opinion 

 is strengthened by the acidic or iron vitriol character which 

 it still retains, and also by the large amount of ironstone 

 (brown hematite or limonite) found on the northern boundary 



