PETEOCKArHICAL CHAltAGTEll OP NEGAUNEE FORMATION. 373 



many Tiim-s greater than in the Islipeiiiino-Negaunee area, where the 

 average diameters vary from less than 0.01 mm. to 0.(13 nun. The (juai-tz 

 grains of the Avestern area are of sufficient size to shnw distincth- undn- 

 latory extinction and fracturing, the latter rarely in a rectangular manner. 

 In the more mashed varieties they are arranged, to some extent, with their 

 axes in a common direction. The griinerite is also coarsely crystallized. 

 Exact comparison with the griinerite of the Ishpeming area is, however, 

 difficult. The jaspers of the western end of the district alford a good 

 opportunity to observe the relations of the included particles of hematite 

 and the grains of quartz. The foi-mer appear just as if they were in their 

 present i)ositions before the silica had taken the remaining space and crys- 

 tallized. There is no tendency to concentration of this hematite at the 

 borders of tlie c^uartz grains or in the cracks formed by their fractur- 

 ing. In the jaspers and in some of the more quartzose griinerite - mag- 

 netite-schists is also a lieautiful concretionar)- structure, exactly similar 

 to that of the ferruginous cherts of the Penokee district. The concen- 

 tric zones of red hematite, separated by a greater or less distance, appear 

 as if })ainted upon the quartzose background, the grains of which seem 

 in no way to be affected by the hematite. The crystals of hematite 

 and magnetite formed still earlier, or else developed where the red 

 hematite and the quartz have been dissolved, for they are scattered at 

 random through the section, interrupting the concentric zones of hematite 

 at many places. In some slides the concretions are decidedly flattened 

 by i^ressure. 



The foregoing facts show that in these jaspers the minerals, with the 

 possible exception of the crystals of hematite and magnetite, had assumed 

 their present relations before the last orogenic movement. The concre- 

 tions, the coarsely crystalline character of the rocks, and the absence of 

 the sideritic and ferruginous slates imply a much more nearly complete 

 recrystallization of the entire formation than has taken place iii the eastern 

 part of the district. If the original rocks in the western part of the district 

 were of the same character as about Ishpeming and Negaunee, the silica 

 must have entirely recrystallize<l. It is to be noted that in this part of the 

 district the other formations of the Marquette series are also much more 



