THE LOWER HURONIAN. 301 



uous narrow monocline of slate extending from Cacaquabic Lake east to 

 Lake Gobbemichigamma, and lying between the high Twin Peaks anticline 

 on the north and the gabbro on the south. This belt of rocks has been 

 much metamorphosed by the gabbro. 



The slates of the Lower Hiu-onian show the effect of the pressure much 

 better than do the conglomerates, and the remainder of the description of 

 the structure of the sediments applies specifically to the slates forming the 

 vipper part of the series. In addition to the close folding, which is indicative 

 of great pressure, the Lower Huronian Knife Lake slates have been jointed 

 and faulted, and schistosity and cleavage have been produced. In general, 

 the major joints have an east-northeast trend, and the cross joints have a trend 

 not quite at right angles to the first. These joints make the slates break 

 into rhomboidal blocks and are the chief cause of the formation of the high 

 cliffs. The strike of the joints varies with the direction from_ which the 

 pressure producing- them came. Thus, in the western part of the area, 

 where the pressure was apparently N. 10° W. to S. 10° E. — that is, perpen- 

 dicularly to the axis of the folds and to the strike of the bedding — one set of 

 joints trends about N. 80° E., and another trends in a direction very nearly 

 at right angles to it, making an angle a little less than a right angle with 

 the first set of joiaits. In the eastern part of the district, however, where 

 the slates abut against the granite of Saganaga Lake and wrap around it, the 

 direction of the joints changes. Thus in sec. 35, T. 66 N., R. 6 W., three sets 

 of joints were noted. The first set strikes N. 25° E., and dips 30° to the 

 northwest, corresponding closely with the strike of the Schistosity. The 

 second strikes N. 10° W. and dips 85° to the west. This agrees with the 

 bedding. The third set strikes N. 60° E. a,nd dips 85° to the southeast. 

 The strike of these joints evidently influences very materially the shape of 

 the lakes in this part of the district. For instance, in the case of the lake 

 in sees. 34 and 35, T. 66 N., R. 6 W., these joints can be seen to determine 

 the long direction of the lake and the trend of the bays. 



In a few places we find that the slates show minor faulting along the 

 joints. No cases were seen, however, where the throw was more than 

 about 1 foot. South of Fox Lake, at a place north 1,915 paces, west 600 

 paces from the southeast corner of sec. 35, T. 65 N., R. 6 W., the interbedded 

 slates and graywackes are broken and slightly faulted. The fault plane 

 runs N. 10° W. The shearing accompanying the faulting has affected a 



