PETEOGEAPniCAL CHAEACTER OF THE BIJIKI SCUIST. 419 



in part of tlie liovnblende and in part of the griiuerite. In different indi- 

 vidnals and slides the two show the greatest variety of iutergrowths. In 

 one or two instances, near the top of the member, siderite is an important 

 constitnent, constituting a matrix in which the other constitnents are set. 

 In other cases, at lower horizons, a little residual siderite is seen, which is 

 surrounded and penetrated by grUnerite or hornblende and magnetite 

 strongly suggesting that these minerals, with the addition of silica, devel- 

 oped from the siderite. Near the base of the Bijiki schist rounded and 

 enlarged grains of fragmental quartz appear within the completely crys- 

 talline interlocking griinerite, magnetite, and quartz. Still nearer the 

 Goodricli (piartzite we have a fragmental quartzose background, in tlie- 

 matrix of which griinerite and magnetite have developed. In both the pura 

 and the impure phases a great deal of garnet appears. It is possible 

 that a part of the griinerite and magnetite is detritus derived from the 

 Negaunee formation, but the extraordinary likeness of the Bijiki schist to 

 the grlinerite-magnetite-schist produced by metasomatic processes from iron 

 carbonate, the presence of siderite in the fonnation itself, the relations of 

 this siderite to the griinerite and magnetite, the absence of any fragmental 

 appearance, all suggest that the rock developed out of an original sideritic 

 slate, similar to that of the Negaunee formation. It is not improbable that 

 the development of the griinerite-magnetite-schist, both in the Upper Mar- 

 quette and Lower Marquette series, was a simultaneous process, occurring 

 during and after the Upper Marquette folding. 



RELATIONS TO ADJACENT FORMATIONS. 



It has been said that the Goodrich quartzite grades rapidly upward 

 into the Bijiki schist. The Bijiki schist in turn grades into the Michigamme 

 formation, the intermediate zone again being half fragmental. Belonging 

 with or immediately above the griinerite-magnetite-schists, in the western 

 part of the district, are the ore deposits of the Upper ]\Iarquette series. 

 These ore bodies appear, however, to be rather within the slates than to 

 belong with the griinerite-magnetite-schist; but if exposures were suili- 

 cieutly numerous it might be possible to map in the Up^jer Marquette series 

 a continuous iron-bearing formation which would include these ore Iwdies 



