418 



THE MAEQUETTE IRON-BEAlilNG DISTEICT. 



the rock is broken into pieces parallel to the stratification, so firmly are the 

 different plates bound together by the long griinerite needles; but it is 

 comparatively easy to break the rock across the bedding. This peculiar 

 toug'hness and the more coarsely crystalline character of the griinerite are 

 the chief points which distinguish it from the similar rock of the Negaunee 

 formation. 



An analysis of the typical Bijiki schist (Specimen 25446, sec 19, 

 T. 48 N., R. 30 W.) north of Michigarame was made by George Steiger, 

 in the chemical laboratory of the United States Geological Survey, with 

 the following result: 



Anali/sis of tijpical Bijiki schist. 



This analysis indicates that the essential constituents of the rock are 

 griinerite and quartz. A ccimparison of the analysis of this rock with the 

 analyses of the griinerite-magnetite-schists of the Negaunee formation 

 (p. 338) shows how A'ery similar they are. The first analysis given of the 

 Negaunee griinerite-schist is very similar indeed to that of the Bijiki schist, 

 and the others differ from the latter mainly in containing- more magnetite. 

 Other specimens of the Bijiki schist might have been selected which are 

 also rich in magnetite. 



Microscopical. — Tlio Ivliids of tlie sclilst free from clastic material consist of 

 intricately interlocking griinerite, magnetite, and quartz, with more or less 

 hematite. The different materials may be uniformly intermingled, but 

 move commonly each is alternately predominant, and this gives the rock a 

 banded appearance. Occasionally the amphibole has a green color, and 

 with this a decided pleochroism, perhaps indicating that it is common 

 hornblende. Not infrequently the same amphibole individual is composed 



