464 THE CRYSTAL FALLS lEON-BEAEING DISTRICT. 



clase, some plagioclase and a little microcline, quartz in varying quantity, 

 . and more or less green clilorite that seems to have been derived from 

 biotite. All the constituents present abundant evidence of the effects of 

 pressure. In the least-crushed rocks the quartz shows undulatory extinc- 

 tions, and the feldspar grains granulation around their edges. As the 

 crushing action increased, the granulation increased, so that the most 

 crushed granites now consist of large grains of feldspar and of quartz in an 

 aggregate of broken fragments of orthoclase, quartz, plagioclase and micro- 

 cline, and a few wisps of green chlorite. Movement in the crushed rock 

 mass has drawn out the granulated aggregate between the lai-ge grains of 

 feldspar into bands and lines, thus producing the schistose structure noted 

 in the hand specimens and in the ledges. In the more highly schistose 

 granites a considerable quantity of new microcline and a small quantity of 

 new plagioclase have developed within the g'ranulated aggregate, and in a 

 few instances muscovite has been found in fairly large plates of pale-yellow 

 color. This muscovite occurs on the contact between the larger quartz and 

 orthoclase grains, but more particularly in the granulated matrix. 



The granites in the area between the Sturgeon River and the Felch 

 Mountain 'tongues are not so abundant as those in the northern area of Base- 

 ment Complex rocks, or in the areas surrounded by the sediments, but in 

 their essential features they are identical with these. Occasionally the sur- 

 face of a fresh fracture through these southern granites shows the outlines 

 of porphyritic orthoclase crystals, but tliese crystals are not sufficiently 

 numerous to impart a porphyritic aspect to the rock. 



Some of the granite specimens examined from this district are so com- 

 pletely granulated that they can with difficulty be distinguished in the hand 

 specimens from the schistose arkoses near the base of the fragmental series. 

 In thin section they differ from the latter in containing no rounded quartz 

 grains and in the possession of A^ery little mica. The feldspathic constitu- 

 ents are nearly all decomposed, and very much of the quartz present in the 

 granites is of secondary origin. 



Thus in all essential respects the gneissoid granites of this district are 

 like those in the Marquette district elsewhere described.^ 



'The Marquette iron-bearing district of Michigan, by C. E. Van Hise and W. S. Bay ley, with a 

 -chapter on the Republic trough, by H. L. Smyth : Mon. U. S. Geol. Survey, Vol. XXVIII, 1897, pp. 

 171-176. 



