148 THE CRYSTAL FALLS lEONBEARlNG DISTRICT, 



waterworn sediiueut can not now be definitely determined, though that it 

 beh)ngs to the first appears more probable. 



Still another rock very similar in general character but differing in 

 detail, and showing a slightly different result, has been examined. The 

 pebbles are basalt, and in them the secondary nature of the biotite, which 

 has chlorite associated with it, is clearly shown. Near the centers of the 

 pebbles very little is present, bnt it rapidly increases in amount toward the 

 periphery, until at the edge only here and there the feldspars may be seen 

 between the mica and chlorite flakes. The cement between the pebbles 

 consists of angular fragments of altered orthoclase feldspar, quartz, and a 

 great quantity of chlorite, and some biotite. This cement is present in 

 large quantity. 



In both of these last the secondary minerals are parallel, and produce 

 rocks of most decided schistose character. These schistose pyroclastics 

 may be compared with the rocks described by Williams^ andBayley" from 

 the related rocks in the adjoining Marquette district. 



THE BO]SnE LAKE CRYSTALEINE SCHISTS. 



Under this name are included certain crystalline schists which are best 

 developed in the northern part of the Crystal Falls district, in the vicinity 

 of Bone Lake. If one examined isolated specimens of certain of these 

 rocks, it would be impossible to determine their origin. Studied in connec- 

 tion with the alteration of the altered and schistose lavas and pyroclastics 

 already described, the jjroblem becomes greatly simplified. These 

 schists, as will be shown on the following pages, are but e:!ftremely meta- 

 morphosed members of the Hemlock volcanic formation. Since in the 

 limited area in which the rocks occur the secondary characters are domi- 

 nant, while the primary volcanic characters have nearly all disappeared, a 

 brief separate description of these rocks seems warranted, but they are not 

 represented by a separate symbol on the map. 



DISTRIBUTION. 



The crystalline schists predominate in T. 46 N., R. 32 W. Near the 

 western limit of this township the belt occupied by these rocks is about 2 

 miles wide. As it is followed to the east past Bone Lake, and then to the 



iBull. U. S. Geol. Survey, No. 62, cit., pp. 185-191. 

 ^Mon. U. S. Geol. Survey, Vol. XXVIII, cit., pp. 160-169. 



