STRUCTURAL GEOLOGY. 11 



Metamorphism of the fragmental rocks.] 



correctly be called mica schist. In this case, however, the boulders and pebbles are still 

 distinctly preserved, becoming more apparent on the weathered surfaces. One of 

 the most perfect examples of the effect of metamorphism and granitic intrusion on 

 the Upper Keewatin is to be seen about Snowbank and Disappointment lakes, and 

 extending westward toward Moose lake. These beds are here penetrated by granite 

 about Snowbank lake and the western confines of Disappointment lake, and 

 by gabbro along the south side of Disappointment lake. The rocks resulting from 

 these intrusions are quite different. The granite seems to have been accom- 

 panied by a wide regional metamorphism, and the gabbro by an intense contact 

 metamorphism. The former permeated the conglomerate in such a manner as to 

 form in general a rock that might be called mica schist, but the schist retains its 

 perfect sedimentary structure, and shows multitudes of pebbles of various kinds, 

 many of them of granite. The gabbro formed a rock which has been styled frequently 

 muscovadyte, but still retains boulders, though less distinctly than in the mica schist 

 at Snowbank lake, and rendered the laminated, sedimentary structure much less 

 evident. The ferro-magnesian element of the gabbro has been presumed to have been 

 transferred by heated circulating water in some measure into the older rock, giving 

 rise to hypersthene, biotite and sometimes olivine and enstatite. At the same time 

 a secondary plagioclase is developed, ranging from andesine to labradorite, which 

 embraces, in the same manner as the hypersthene and often as the magnetite, nearly 

 all the other minerals poikilitically. But this hypothetical loss of ferro-magnesian 

 minerals by the gabbro is subject to considerable difficulties, viz.: (a) The ferro- 

 magnesian element in this modified rock is frequently equal to or exceeds the same 

 that would be found in any normal gabbro; (b) The gabbro does not show any notice- 

 able loss of these elements at the points of contact; (c) But rather possesses, as a 

 rule, a greater abundance of these minerals. 



Magnetite occurs in abundance locally in this metamorphosed rock. This is the 

 case at Disappointment lake, where it has given rise to exploration for economic 

 results. In some of the annual reports this iron ore was classed with the Animikie. 

 It resembles the iron ores supposed to be Animikie where they have been affected by 

 the gabbro, such as seen at the Gunflint Lake Iron company's works near Gunflint lake, 

 and at Birch lake, but this resemblance is due apparently to the similarity of the 

 original ores and the identity of the rock that caused the metamorphism. The two 

 ores were hematite (occasionally magnetite) with silica as the principal impurity. 

 The action of the gabbro has resulted in the re-formation of both substances, the 

 resulting magnetite serving sometimes as a mesh or sponge in the spaces of which 

 are found grains of secondary quartz and of nearly all the ferro-magnesian minerals 

 of the muscovadyte. This deposit of iron, therefore, is to be parallelized with that 



