THE LOWER HURONIAN. 293 



Ely greenstone, as well as predominant pebbles of the granite rocks of 

 VeiTQilion Lake. This is the point nearest to the basal greenstone at which 

 the conglomerate has been found in this part of the district. 



Another basal conglomerate somewhat similar to the one just described 

 occurs on the south side of the county road leading from Tower to Pike 

 River, about 325 paces east of the bridge over West Two Rivers. This 

 conglomerate has been sheared until it is quite schistose. It consists 

 chiefly of fragments of greenstone, jasper, and feldspar-porphyry. 



KNIFE LAKE SLATES. 



The conglomerate described in the preceding pages is overlain by the 

 important Knife Lake formation, which is excellently developed upon the 

 shores of Vermilion Lake in the vicinity of Tower. The name is given 

 to the formation on account of its typical development near Knife Lake 

 (p. 297). 



PETEOGKAPHIC CHARACTERS. 



It has been stated that the dividing line drawn in the Lower 

 Huronian sediments between tlie Ogishke conglomerate and the Knife 

 Lake slates is purely arbitrary. The transition between them is not 

 sharp. Among the conglomerates there are a few interbedded fine- 

 grained sediments, and among the slates there are a few fragmentals that 

 are coarser than the normal slates, and show gradations between the slates 

 and the conglomerates. However, the slates are by far the predominant 

 kind of rock in the areas marked on the accompanying maps with the 

 slate color, the grits playing a very subordinate role. 



Corresponding to differences in mineralogic character there is in the 

 slates considerable variation in color and texture. The normal slates are 

 on fresh fracture generally a slate gray to dtirk-greenish gray, and even 

 light greenish. Sometimes they range through purplish and bluish-black 

 rocks to a dense and almost black slate. They usually weather with a 

 light-gTa}^ to brown crust. The grain of the slates is so fine that one can 

 distinguish no individual mineral, unless it be quartz, except in the phase 

 that approaches the grits. The banding in the slates is caiTsed by slight 

 variations in the quantity of the minerals of different color constituting the 

 slates, and by a slight difi'erence in size of grain. These bands within the 



