18G7.] MACFARLANE — GEOLOGY OF LAKE SUPERIOR. 197 



It exhibits numerous divisional planes and a tendency to slaty 

 structure, the direction of which is not, however, parallel with 

 that of the divisional planes. It contains numerous fragments 

 and long drawn contorted masses of granite, which are best dis- 

 cernible on the worn surface of the rock, and not readily so where 

 it is freshly fractured. To the eastward it changes to a much 

 harder light grey siliceous rock, having a specific gravity of 2-709 

 only. In fine powder this rock is white, but on ignition becomes 

 brownish, and loses 0-55 per cent, of its weight. It yields only 

 4-62 per cent, of bases to sulphuric acid. At one place it seems 

 to contain fragments and twisted pieces of the dark greenstone, and 

 further eastward it assumes the character of a breccia, granite 

 fragments being enclosed in the slaty rock, which is at some points 

 darker, at others lighter, coloured. The fragments are sometimes 

 quite angular, and sometimes rounded oif, and not sharply separ- 

 ated from the matrix. Their longer dimensions are invariably 

 parallel with the lamination of the matrix. The distance over 

 which the transition extends renders it impossible to give any ac- 

 curate sketch of the phenomena described. 



Similar relations are observable at the junction of the two 

 formations in the north-east corner of Bachewahnung Bay. Here 

 the greenstone is compact, but still possesses the glittering basaltic 

 fracture. The Laurentian rock is a highly granitic gneiss, and 

 pieces of it are enclosed in the dark greenstone, which at one place 

 seems to underlie the granite. A reddish grey felsitic rock, with 

 conchoidal fracture, is observed at the point of junction. East- 

 ward from it banded traps occur, striking N. 55° W., together 

 with greenstone — breccia, and conglomerate. On ascending the 

 hills behind this point another breccia is observed, of which the 

 matrix is greenstone and the fragments granite. 



With regard to the succession of these rocks, it will doubtless 

 be found a matter of very great difficulty to establish any such, 

 even if any order of superposition of a tolerably regular character 

 should exist among them. That this is not very likely to be the 

 case, will appear from the considerations yet to be advanced re- 

 garding the origin of these rocks. As to their general strike, it is 

 scarcely possible to give any such, but within certain limits a 

 tolerably constant strike may be observed. In the Huronian area, 

 betwixt Goulais River and Bachewahnung Bay, although there are 

 occasional north-easterly directions, the strike generally ranges 

 from N. 40° to N. S0° W. On the north shore it is generally 



