414 THE MARQUETTE lEON-BEAEING DISTRICT. 



is a continuous ramifying mass wliieli contains the separate pebbles and. 

 bowlders. Tliis matrix may be composed chiefly of any one of the sub- 

 stances, iron oxide, chert, jasper, or quartz, or of any combination of them. 

 Not infrequently some secondary muscovite has also developed. Often 

 the quartz grains are enlarged. In all cases the simple quartzes show 

 imdulatory extinction and fracturing. In the resultant and other crevices 

 secondary hematite and magnetite were deposited. Where the mashing 

 was great the fragments of chert, jasper, and quartz were flattened into 

 thin, layer-like areas, and in this case a slide of the recomposed rock 

 differs but little in its appearance from the original jaspilite. Accompany- 

 ing the granulation of the ore, chert, and jasper, the hematite was sheared 

 into brilliant, finely laminated, micaceous, or silky fibrous hematite. Flakes 

 of muscovite are usually seen. The secondary magnetite and hematite are 

 easily discriminated from the sheared micaceous hematite by having crystal 

 outlines. This infiltrated material is frequently present in very large 

 proportion, filling all the interspaces between the original ])articles and the 

 cracks formed within the fragments. In some cases the secondary hematite 

 and magnetite have such relations to the quartz grains as to sliow that the 

 silica was actually dissolved and replaced by the iron oxide. To what 

 extent this occurred where the rocks are much mashed it is difficult to say, 

 but in the little-altered phases we find crystals of hematite and magnetite 

 whicli not only pass to the borders of the cores of the enlarged grains but 

 into them. There seems to be some relation between the solution of quartz 

 and the deposition of magnetite; that is, when the conditions are favorable 

 for the deposition of magnetite they are also favorable for the solution of 

 quartz. 



The most mashed phases of recomposed jaspers have very much the 

 same appearance as those of the original jasper formation, but when 

 examined with a low power the overlapping lenticular leaflets of the 

 mashed chert and jasper fragments are seen, and a high power shows in 

 some cases a micaceous mineral which is almost invariably absent in the 

 original formation. In the less mashed phases of the recomposed jaspers 

 their genesis is more plainly indicated by the presence of coarse-grained 

 quartzose material, not derivable from the immediately subjacent formation; 



