THE LOWER HURONIAN. 299 



growth, partly by reason of extensive forest fires and partly for lack of 

 good and abundant soil; consequently the exposures of these sediments are 

 numerous and usually of exceptionally large size. 



Topography. — The topography of the Knife Lake area of the Lower 

 Hui'onian sediments is very rough, although the features as a whole are on a 

 comparatively small scale. In general the topography in this area is much 

 more accentuated than it is in the area underlain by the same sediments in 

 the western portion of the district already described (p. 278). The maxi- 

 mum difference in elevation is 400 feet, the difference between the level of 

 Ogishke Muncie Lake and the adjacent hills. Reference has already been 

 made (see p. 45) to the fact that the lakes in this part of the district are rela- 

 tively deep, as has been shown hj the few soundings taken. The maximum 

 depth found in a lake in the sediments is nearly 200 feet. In reality, then, 

 the difference between lowest valleys and lake basins and highest hills is 

 about 600 feet. The hills and ridges have the ixsual east-northeast-west- 

 southwest trend, with narrow, deep valleys occupied by streams and lakes 

 lying between. The slates, on the other hand, generally form the lower 

 hills. These, while occasionally rounded, are generally more or less angu- 

 lar, more nearly corresponding to the appearance of the slate hills in non- 

 glaciated territory, although by no means so angular as these. 



Normally the conglomerates occupy higher levels than do the slates 

 which lie next to them, and these hills of conglomerate have fairly well- 

 rounded contours. In portions of this area, however, the slates are very 

 siliceous, and as a result of their great hardness form some of the highest 

 hills. In the area underlain by slates sheer cliffs are common, some of 

 them reaching' a height of 100 feet above the lakes. 



The topography has been greatly influenced by the structure. This 

 will be referred to in the succeeding paragraphs. 



structure: 



The Lower Huronian sediments, from the westernmost point where 

 they are found (see PI. II), just west of Ely, to their eastern extension, where 

 they abut against the Saganaga anticlinal area, occupy a spiclinorium 

 which trends approximately N. 70° E. and continues around the northern 

 side of the Saganaga anticlinal area into Canada. This synclinorium is 

 narrow in its western part and widens out toward the east. In that portion 



