320 THE MAEQUETTE IRON BEARIiJG DISTRICT. 



of mica or of chlorite, which are often bent or contorted, but these appear 

 to be fraginental. 



In a still more advanced stage of metamorphism the larger quartz 

 grains are partly granulated, secondary quartz is jDresent, the whole of the 

 feldspar is decomposed, and we have a fine-grained mica-slate. In many 

 places these mica-slates are interlaminated with coarser-grained layers, 

 which distinctly show the clastic origin of the rock. In a single section 

 there may be a number of alterations of mica-slate and micaceous gray- 

 wacke. Sometimes the fissility is well developed in the mica-slate, and 

 abuts diagonally against the laminae of graywacke, in which it is less 

 prominent or absent altogether. In the most extreme stage of metamor- 

 phism the coarse, fragmental grains of quartz, if there were any, were 

 granulated, and the secondary quartz is as coarsely crystalline as this 

 original quartz. The grains of varying sizes fit closely or interlock. The 

 mica and chlorite are in well-developed parallel blades of considerable size, 

 and thus the rock is a mica-schist. In one phase of the mica-schist are 

 numerous large crystals of chlorite, which have their cleavage transverse 

 to the schistosity. They include numerous grains of quartz. , These have 

 probably developed under static conditions after the dynamic action had 

 ceased. In some of the mica-schists is a considerable amount of clear 

 feldspar, which looks as though it wei-e in part a secondary development, 

 and thus the rock approaches a mica-gneiss. Although the Siamo forma- 

 tion thus locally becomes a completely crystalline schist, in that it no longer 

 shows in itself any distinct evidence of original fragmental character, the 

 gradation phases enable one to determine its manner of development as 

 above given. 



Where the slates and graywackes pass into the feiTuginous varieties 

 there appears in the matrix more and more of iron oxide, generally hematite, 

 l)ut in many cases magnetite also. These increase in quantity until there 

 are more or less continuous, nearly solid layers of iron oxide, and in the 

 extreme stage of ferrugination the matrix is so heavily iron-stained that 

 little else can be discriminated. Where the iron oxide is magnetite, this is 

 apt to take definite crystal outlines. In most cases it is plain that the 

 oxides of ii'on are secondary infiltrations, being in part in crystals, and in 



