TOPOGRAPHY 297 



from 20 to 60 feet of slimy mud covering the rock bottom. This lake 

 has no visible tributaries, but is, of course, fed by the rainfall of the 

 upper end of the valley. The small stream flowing out of it has not 

 cut any appreciable channel, and the same is true of the stream from 

 Sayers lake, which is stated to be about as deep as Boyer lake and with 

 the same muddy bottom. One can walk round both lakes with solid 

 rock in sight the whole way, so that there can be no doubt that the 

 basins are inclosed by rock. In a few places the rock shelves gently 

 into the basins, but generally forms steep slopes or even cliffs at the 

 water's edge. 



Geological Conditions 



In order to understand how the valley was carved it is necessary to 

 give an outline of its geological structure. The lake basins are almost 

 entirely inclosed in rocks of the Lower Huronian iron range — granular 

 silica interbanded with iron ore toward the north, and the same with 

 pyrite or else siderite toward the south. The steep slope of Hematite 

 mountain and its summit consists chiefly of somewmat pyritous and 

 silicious siderite. On each side of the band of iron range rock, which 

 is about 1,000 feet wide, are greenish schists, mainly sheared quartz-por- 

 phyry — the rock usually found underlying the iron range in the region. 

 Part of the southern shore of Boyer lake consists of the quartz-porphyry 

 schist, with a narrow dike of greenstone, now schistose also, so that its 

 basin is not wholly inclosed by the iron range. The northern side of 

 the iron range is very hard and cherty or quartzitic and has resisted the 

 weather even better than the schist, so that it forms the highest part of 

 the ridge. 



The eastern end of Boyer lake does not reach the foot of Hematite 

 hill, since that part of the basin is occupied by the ore body which will 

 be referred to again. 



Professor Willmott, who has studied the geology of the Helen mine in 

 detail, represents the arrangement as synclinal, toward the western end 

 complicated by the rising of a small anticline in the middle. The iron 

 range is, of course, inclosed and folded within the thick series of schists 

 forming the bulk of the Lower Huronian, and the date of the folding is 

 very ancient, almost certainly pre-Cambrian. When the folding took 

 place we can imagine the tough schists as yielding without much break- 

 ing ; but the more brittle iron-range rocks were greatly crushed, and a 

 large amount of breccia was formed of fragments of granular silica, as 

 may be seen along the north of the basin, especially on the shore of 

 Savers lake. 



