434 THE VERMILION IRON-BEARING DISTRICT. 



The shapes of many of the lakes, especially those which lie com- 

 pletely in rocks of more or less uniform character, have been determined 

 by the direction of the joint planes of the district. The major joints agree 

 very closely with the direction of the predominant schistosity and trend 

 N. 60-80° E. The next important system of joints is approximately at 

 right angles to that direction. The effect of this jointing can be seen best 

 in the lakes lying within the well-jointed Knife Lake slates. Knife Lake 

 itself shows its dependence upon the jointing of the rocks by its principal 

 direction, which agrees with the jointing, and by the occasional arms 

 nearly at right angles to it. The main southeast arm of Knife Lake owes 

 its direction, as can be readily seen by reference to the maps in the atlas, 

 to the influence of the Archean anticline which forms its north shore. The 

 lakes between the east end of Knife Lake and Saganaga Lake are within 

 the area wherein the influence of the anticline formed partly of the granite 

 of Saganaga Lake makes itself felt, and where as a result of this the bed- 

 ding of the slates, as well as the jointing, which agrees fairly well with the 

 direction of bedding, turns strongly to the east of north, getting more nearly 

 north, and finally turning a little to the west of north as the northern portion 

 of the granite mass is approached. This change in direction of the structure 

 in the slates and the relationship of the extension of the lakes thereto is 

 shown by the string of lakes in sees. 26, 34, and 35, T. 66 N., R. 6 W., and 

 sees. 3 and 10, T. 65 N, R. 6 W. This string of lakes connecting the east end 

 of Otter Track Lake and the east end of the south arm of Knife Lake has 

 a trend in general of N. 20° E. Another specific instance of the influence 

 of the jointing in these slates can be seen in the lakes in sec. 30, T. 66 N., 

 R. 5 W., and sees. 24-25, T. 66 N., R. 6 W., just west of the boundary 

 between the Knife I^ake slates and the granite of Saganaga Lake. Here 

 the jointing and the bedding have turned to about N. 10° W. These two 

 lakes have their major direction following this line of major jointing. A 

 second system runs N. 25° E. and controls the trend of the ends of some of 

 the points and the greatest width of the lakes. 



Another factor which has in many cases determined the position of the 

 topographic features has been the plane of contact between the different 

 formations and the differential erosion of these formations. A notable case 

 is that of Otter Track Lake, on the international boundary. This lake lies 

 along' the contact of the Archean erreenstone and the Lower Huronian Knife 



