160 THE MARQUETTE IKON-BEARING DISTRICT. 



possible that tliey could be fragments produced by the crushing' of crystals. 

 Besides, these white or pink schists and the green ones occur side by side 

 in the same ledge, and the two apparentl)' grade into each other. 



In many of the sections cut from the acid rocks only quartz and sericite, 

 with perhaps a little epidote, can be discovered. The three minerals form 

 a very fine gi-ained aggregate, resembling strongly the mosaic of many 

 devitrified rhyolites. The tiny quartz grains are separated from one another 

 by flakes of sericite, arranged with their longer axes in a single direction. 

 At present the rocks are sericite-schists. In a few of them obscure traces 

 of feldspathic fragments may be detected when their sections are examined 

 with low powers between crossed nicols, but from most of them every trace 

 of fragmental material has disappeared and the rocks are now thoroughly 

 crystalline. 



Schists like these have been described by Williams,^ Avho regards them 

 as metamorphosed acid tuffs. They may ])ossibly have been acid sheets 

 interstratified with the basic lavas and tuflPs that formed the greenstones, 

 but when the fact is considered that they grade imperceptibly into the green 

 schists and that in some of them ti-aces of fragments may be recognized, it 

 seems more ])robable that they were, as Williams supposes, originally acid 

 tuffs which have been altered and made schistose by processes similar to 

 those that changed the diabasic lavas and tuffs into the greenstone-schists. 



THE KITCHI SCHISTS. 



Many of the green schists of the Northern Complex are noticeable for 

 the pebble-like and bowlder-like bodies scattered through them. These 

 fragments stand out so plainly on the weathered surfaces of the exposures 

 on the Kitchi Hills in the vicinity of Deer Lake (Atlas Sheet XXVII) that 

 thev may be seen from long distances. They are usually so well rounded 

 that the rock containing them looks very nuich like a sedimentary con- 

 o-lomerate. Indeed, so conglomeratic are their features that they have 

 frequently been called the Deer Lake conglomerates. (See fig. 4.) The 

 rocks are, however, jjlainly basic tuffs, Ijut they have preserved their 



'The greenstouo-scbist areas of the Menoniiuee and Marquette regions of Michigan, by G. H. 

 Williams: Bull. U. S. Geol. Survey No. 62, 1890, p. 151 



