EXPOSUKES OF THE IJIJIKI SCHIST. 417 



of the Goodrich quartzite to the east. ^Vhere the Bijiki formation a])])ears 

 the Goo(h-ifh quartzite becomes an exceedingly narrow belt, too small to 

 be shown on the atlas sheets; hence the two are mapped together as the 

 Ishpeming formation. 



The lock is of a resistant character, and for the areas outlined there 

 are numerous exposures. South of Michigamme and 8purr it makes con- 

 spicuous east-and-west ridges just north of the railroad For most of the 

 length of Lake Michigamme the southern border of the central resistant 

 belt forms the northern lake boundary. Howevei', at two or three jjlaces 

 the schist was cut through and the lake shore follows the softer formation 

 to the nortli. In two of these cases the Bijiki schist constitutes headlands 

 lapped on three sides by water In the same way the southeastern shore 

 of Lake Michigamme is limited In- the southern belt of this schist At 

 various places erosion encroached upon the belt, but the rock is so resistant 

 that the lake nowhere cuts entirely across the formation. 



FOLDINO. 



The belts adjacent to the Goodrich quartzite owe their position to their 

 being the next higher horizon in the general synclinorium of the district. 

 The central belt is due to a subordinate anticline which rises high enough 

 to expose the Bijiki schist, but erosion has not reached a lower horizon, and 

 thus a section across the area, including the tlu'ee formations, shows two 

 synclines with a central anticline. 



PETROGKAPHICAL CHARACTER. 



Macroscopicai. — Tlic Bijiki schist is a Ijanded griinerite-mag'netite-schist. 

 Associated with this rock are also phases which approach the ^lichigamme 

 slate ab(ive and the Goodrich (juartzite below. These are nsualh' gradation 

 phases, and occur upon the outer parts of the belt. (PI. XXXI ) The 

 griinerite- magnetite -schists consist of bands composed mainly of the 

 three minerals, quartz, griiuerite, and magnetite, and while in anj- single 

 band one of these minerals may be predominant, the other two are usually 

 present. The rocks are gray or green, and in their nearly pure phases 

 they differ from the griinerite - magnetite - schist of the Negaunee forma- 

 tion chiefly in their exceeding toughness. It is with great difficulty that 

 MON xxviii 27 



