INTERESTING LOCALITIES OF THE ISIIPEMING FOKMATION. 421 



overlying- the ore. The rehitions of the Neg;uinee jasper, the ore, and the 

 conglomerate are shown by fig. 26. At the Spurr mine the conglomerate is 

 at least 40 feet thick. The conglomerate at both mines passes up rather 

 abruptly into a greenish or grayish, massive quartzite. This quartzite in 

 turn varies by interstratification into the griiuerite-magnetite-schist which 

 has been called the Bijiki schist. (PI. XXXI.) An intermediate variety 

 is a fine-grained biotitic and griineritic gi'aywacke. Not more than 50 

 feet south of the interlaminated beds are typical exposures of the Bijiki 

 schist. This quartzite at the Michigamme mine is folded into a series of 

 minor rolls, which are cut by dikes. (PI. XXX.) At the Spurr and Michi- 

 gamme mines, on the south or hanging-wall side of the pits, are dikes of 

 chlorite-schist, which are taken to be modified eruptives, as they cut the 

 other rocks like dikes. It is in and adjacent to tlie chlorite-schists that 

 the large garnets and chlorite pseudomorphs after garnets described by 

 Pumpelly are obtained. The entire thickness of the Goodrich rock is 

 perhaps not more than 100 feet. The Bijiki schist occurs in very numei-ous 

 exposures on the hills between the mines and the railroad track, and 

 particularly on a prominent ridge just north of the railroad track lietween 

 the two mines. The boundary between the Ishpeming formation and the 

 Negaunee formation follows a low and sometimes swampy area. In all 

 respects the Bijiki schist of this locality corresponds to the general descrip- 

 tion (pp. 417-418). The rock is minutely crenulated, and, Avhile ha%dng a 

 general southward dip, has many minor, often is(x-linal folds. 



As seen in thin section the majority of the quartzites are composed 

 of rather well-rounded grains of quartz having a matrix of chlorite or of 

 chlorite with biotite and magnetite. With the fragmental grains of quartz 

 at the Spurr mine are also fragmental grains of feldspar and small granitic 

 pebbles. Most of the grains of quartz are so large that they could nt)t 

 have been derived from the Negaunee formation, and they very probably 

 come from the granite of the Basement Complex. That this is their 

 source is indicated by the feldspar and the granitic fi-agments. Little or no 

 fragmental material from the Negaunee formation was detected. It thus 

 appears that shortly after the Goodrich quartzite began to form, tlie thin bed 

 of conglomerate buried the Negaunee formation in the immediate vicinity, 



