514 THE MAEQUETTE lEON-BEAEING DISTEICT. 



the garnets. The garnets are identical in natiu-e with the garnets in the 

 gametiterous knob greenstones. They are pei-fectly isotropic. In color 

 they are very light pink, almost colorless. Their principal inclusions are 

 magnetite, but they always inclose also small quantities of chlorite, quartz, 

 biotite, altered feldispar, and often crystals of pyrite and needles of 

 actinolite. In all cases the garnets are crossed by great fi-acture cracks, 

 which are sometimes so coai'se that they give the crystals a granular 

 appearance. In these rocks the garnets, although idiomorphic, appear to 

 be the youngest component present, with the exception of the biotite, which 

 suiTOunds them periphei-ally, and which must be regarded as constituting a 

 reaction rim. 



Other garnetiferous dike greenstones are more like mica-hornblende- 

 schists than like chlorite-schists. They contain large quantities of quartz, 

 and are thus similar to the quartzitic greenstones of the Republic and Mag- 

 netic mines, from which they differ mainly in the possession of garnets. 

 In these latter rocks the garnets are often granulated, as though the rock 

 in which they occur had been mashed after their formation. 



From the above description it is noticed that the garnetiferous schists 

 differ from the other schistose geeenstones simply in the possession of gar- 

 net and in some cases of griinerite, both of which minerals are found as 

 normal constituents in the griineritic schists through which the greenstones 

 cut. The inference from these facts is that the garnetiferous rocks are not 

 contact rocks in the usual sense, but that their peculiar features are due to 

 reactions between solutions passing between the intruded and intruding 

 rocks and carrying dissolved salts from the one into the other. Mechauieal 

 action may also have been instrumental iu the formation of the new products 

 in the schists, but it is not believed that the heat of the dikes was at all 

 effective in their production. The phenomena are believed to be those of 

 metasomatism and of dynamic metamorphism rather than of contact action. 



THE SHEETS AND TUFFS. 



Only a few undoubted sheet eruptives and a small number of areas of 

 volcanic fragmental rocks have been positively identified in the beds older 

 than the Clarksbm-g- formation. In one or two instances the sheet rocks 



