1867.] MACFARLANE— GEOLOGY OF LAKE SUPERIOR, 201 



Besides the black and greenish black dykes which occur in the 

 neighbourhood of, and stand in connection with, Huronian rocks, 

 there are others which occur at a distance from Huronian areas, 

 and whose rocks differ somewhat from those of that formation. 

 This is the case, for instance, with a set of dykes which occur on 

 the south-east shore of Goulais Bay, cutting Laurentian rocks. 

 They are there separated from the gneissoid rocks by very distinct 

 joints. They vary in thickness from nine to seventy feet, and 

 strike N. 72° to 75°, W. In the widest veins the rock is fine 

 grained at the side and small grained in the centre, so that even 

 there it is difficult to determine its constituents. They seem, 

 however, to be dark green pyroxene and greyish felspar, with 

 magnetic and minute grains of iron pyrites. The rock has a 

 specific gravity of 2-97-1. Its powder, from which a magnet ex- 

 tracts magnetite, has a grey colour, which changes on ignition to 

 a dirty brown, with a loss in weight of 1-67 per cent. Hydro- 

 chloric acid produces no effervescence, but removes 21-74 per cent. 

 of bases. Sulphuric acid removes 20-83 per cent. The presence 

 of magnetite and absence of chlorite would seem to indicate that 

 the rock inclines more to the nature of dolerite than diabase. A 

 similar vein of fine grained rock penetrates the syenite of Gros 

 Cap, on the summit of that hill, striking N. 40 ° W. A very 

 large mass of small grained doleritic rock likewise occurs at the 

 mouth of the Montreal River, on its south bank. It probably 

 forms a dyke of very large dimensions in the granitoid gneiss 

 there. It consists, seemingly, of black augite, white or greyish 

 white felspar (on some of the cleavage planes of which parallel 

 striae are distinctly observable), and magnetite. Its specific 

 gravity is 3-090. Its powder yields magnetite to the magnet, and 

 does not effervesce on treatment with sulphuric acid, which re- 

 moves 11-15 per cent, of bases. - Other dykes of this nature cut 

 the reddish granite of the north shore opposite Michipicoten 

 Island, and, nearer to Michipicoten Harbour, a sixty feet dyke of 

 diorite cuts the grey granite. It is fine grained at the sides, but 

 granular and even porphyritic in the centre. Its direction is N. 

 63 ° E. About a mile further east another dyke occurs, which 

 seems to contain fragments of granite. Close to the landing-place 

 of the Begley Mine, in Bachewalmung Bay, a dioritic dyke, bear- 

 ing N. 80 ° E., cuts gneissoid rocks Further investigation is 

 necessary to determine what relation, if any, these dykes bear to 

 the Huronian series. 



(To be continued.) 



