342 THE VERMILION IRON-BEARING DISTRICT. 



The microscopic study of these contact rocks of the granite shows 

 nothing of especial interest. The rocks are, as said, mica- (biotite-) and 

 amphibole-schists. The minerals coustitnting them are biotite and some 

 muscovite, hornblende, actinolite, quartz, feldspar, epidote, and garnet 

 occasionally. 



Contact effect of the gabbro. — The effect of the intrusion of the Snow- 

 bank and Cacaquabic granites on the surroimding sediments has been, as 

 said, to produce mica-schists, and, in a subordinate degree, amphibole- 

 schists. Subsequent to this intrusion these schists must have been affected 

 by orographic movements, but the effect of these movements is not recog- 

 nizable, for at a still later date the great Keweenawan gabbro was intruded 

 into the rocks of this district and produced important contact effects upon 

 them. It is practically impossible now to discriminate between the products 

 of these different periods of metamorphism. In general the sediments in 

 the vicinity of the granites and gabbro have been transformed into mica- 

 schists and amphibole-schists, whose chief characters may have been pro- 

 duced by the intrusion of the Snowbank and Cacaquabic granites alone. 

 South and southwest of the Snowbank granite, however, in the vicinity of 

 the gabbro, fine-grained rocks are very commonly spotted and resemble the 

 so-called spilosite, the spotted contact rocks of the. diabase. This peculiar 

 phase of the metamorphism is probably due to the contact action of the 

 gabbro. Some of these spotted rocks are at present about three-fourths 

 of a mile away from the nearest exposures of the gabbro. It is, however, 

 not necessary to believe that the gabbro was able to affect the sediments at 

 this distance. It seems almost certain that at one time the gabbro extended 

 farther north than the line where its present northern boundary appears, 

 and that at that time it overlay these rocks, so that in reality it was sepa- 

 rated vertically from the rock at the level of the present exposures by 

 perhaps, only a few hundred feet of intervening rock at most. Similar 

 spotted rocks occur in the slates upon the prominent hill north of the west 

 end of Paul Lake, in sec. 32, T. 65 N., R. 5 W. The total absence, near 

 these spotted sediments in this area, of any acid intrusives which could have 

 produced them, and their presence here in close proximity to the gabbro, 

 seems to show pretty conclusively that the spotted rocks in this place, as 

 well as the similar ones mentioned above as occurring south and south- 

 west of the Snowbank granite, are due to the gabbro contact action, and 

 not to that of the granite. 



