106 THE PENOKEE IKON-BEARING SERIES. 



The Western gramte. — The gl-auites and gneissoid granites of the 

 western area are classed together, as they differ but little from each other. 

 The gneissoid granites vary in character from those so coarsely schistose 

 as to be with difficulty distinguished from the granites to those which are 

 extremely contorted and quite finely foliated. Although the area is large, the 

 rocks included within it 'are petrographically of essentially the same char- 

 acter. The massive phases are relatively infrequent, and are medium 

 grained granites. Those phases which are most foliated are somewhat finer 

 grained. Tlie rocks of the area vary from almost white to quite a deep 

 red, depending upon the coloration of the feldspar, which mineral is tlie 

 preponderating constituent, the iron-bearing silicates and quartz being 

 usually in subordinate quantities, but not infrequently jdentiful enough to 

 gi^-e the rocks a strongly mottled appearance or even a dark gray color. 

 The normal rocks of the area (PI. xiv, Fig. 1), when examined under the 

 microscope, are seen to l)e composed very lai-gely of alkaline feldspars, 

 including the species orthoclase, microcline, and acid plagioclase. The 

 feldspar is usually in individuals of nearly unifoi-m size which show more 

 or less perfect idiomorphic outlines. With most individuals the average 

 greatest dimensions are less than h mm., although occasionally individuals 

 are found which run up to 4 mm. Frequently the feldspars interlock with 

 each other, in which case the crystal outlines are more or less broken, 

 although the regular forms are to some extent maintained. The only 

 important iron-bearing silicates i)resent are biotite and chlorite. These 

 minerals occur at times included within the feldspars, but more frequently 

 are found in the spaces between them. The chlorite often occurs in well 

 defined blades liaving a rectangular extinction, and appears at times to be 

 secondary to biotite, although often it is in part secondary to feldspar. 

 Occasionally a little muscovite is found included within the felds|)ar. 

 Quartz has been the last mineral to crystallize and has filled up the spaces 

 left by those previously mentioned. It occurs in small roundish or irregular 

 areas between the feldspars, giving the rock a completely interlocking 

 crystalline character. In one or two cases the quartz and adjacent feldspar 

 have a pegmatitic structure. This may signify that the quartz and feldspar 

 in the final stages of crystallization were forming simultaneously, or that 



