422 THE MARQUETTE IRONBEARmG DISTRICT. 



and the fragmental material for the quartzite was transported by the waves 

 from the Basement Complex, wliich at some not distant point was above 

 the water. The grains of quartz all show pressure effects by undulatory 

 extinction and fracturing, and they do not commonly show distinct enlarge- 

 ment, although minute in'egularities, which indicate that they have prob- 

 ably grown, are seen. In some cases the enlargements are distinct. The 

 feldspars, where present, show partial decomposition into interlocking chlo- 

 rite, muscovite, biotite, and quartz. Tlie chlorite in the interstices of the 

 grains is usually in aggregates of minute leaflets, but rarely it occm's in 

 blades of considerable size. Hornblende is found in some slides between 

 the grains of the quartzite. Gxarnet is occasionally present. 



In the variety of rock intermediate between the quartzite and the 

 Bijiki schist the coarse-grained fragmental quartz is clearly discriminated 

 from the fine-grained quartz, which developed in another way. These 

 rocks may be described as hornblendie and magnetitic schists which con- 

 tain numerous clastic grains of cpxartz. In some of them there remains a 

 -considerable amount of siderite, and out of this siderite, joined with silici- 

 fication, the magnetite, hornblende, and quartz have developed, exactly as 

 from the sideritic slates of the Negaunee formation. In the half-frag- 

 mental phases, wherever the siderite is found, griinente and magnetite 

 appear; where fragmental quartz is abundant they are not prominent. It 

 therefore appears that the original transition rock was here a siderite 

 which contained a certain amount of fragmental material. By compari- 

 son (pp. 321-322, 333-334) it will be seen that the rock is analogous to the 

 ti-ansition form between the Ajibik quartzite and the Negaunee formation. 

 Another analogy between this transition rock and that of the Negaunee 

 formation is the fact that the amphibole which develops is pleochroic rather 

 than nonpleochroic. The cause is doubtless the same in both cases — the 

 presence of a great variety of chemical elements in a mingled clastic and 

 nonclastic sediment from which material could be drawn. 



By disappearance of the fragmental quartz and replacement of the 

 pleochroic amphibole by the nonpleochroic griinerite the rock passes into 

 the typical Bijiki schist, which is either a griinerite-magnetite-rock or a 

 griinerite-magnetite-schist. In these rocks there are still found varieties 



