18G7.] MACFARLANE— GEOLOGY OF LAKE SUPERIOR. 



195 



there are others which seem to consist of quartzite. An idea of 

 the structure of this rock is attempted to be given in figure 5. 



Fig. 5. 



a. Granite boulders, and long drawn masses. b. Schistose matrix. 



The manner in which these rocks are occasionally associated 

 with each other is calculated, as in the case of the Laurentian 

 rocks, to suggest to the observer some definite ideas regarding 

 their origin . Equally instructive is the manner in which they 

 adjoin the Laurentian areas at several points on' the north shore, 

 between Michipicoten Harbour and Island. I paid some attention 

 to that point of junction which lies to the west of Eagle River, 

 the precipitous cliffs to the east of which consist principally of 

 diabase schist and greenstone slate. A few miles to the west of 

 these cliffs, and at a point bearing N. 29 ° E. from the east end of 

 Michipicoten Island, the Laurentian granite is penetrated by 

 enormous dykes of dense basaltic greenstone (having the peculiar 

 doleritic glitter when fractured), wliich contain fragments of 

 granite. This greenstone is also seen in large masses, which can 

 scarcely be called dykes, overlying the granite and enclosing huge 

 masses of that rock, one of wliich I observed to be cut by a small 

 vein of the greenstone. From this point to Eagle River those 

 two rocks alternately occupy the space along the shore, seldom in 

 such a manner as to show any regular superposition of the green- 

 stone on the granite, but almost always more or less in conflict 

 with each other. The greenstone, however, becomes more frequent 

 towards the east, and at Eagle River it has almost wholly replaced 

 the granite, and assumed a lighter colour and an irregular schistose 



