372 THE MARQUETTE lEON-BEAEING DISTRICT. 



and crystalline hematite and magnetite. This quartz is much more coarsely 

 crystalline than the older quartz, the grains oftentimes averaging from 0.05 

 to 0.1 mm. in diameter. While nmch of this secondary quartz occurs in 

 veins which cut across the original lamination of the rock, a great deal of It 

 was deposited parallel to the lamination. Its likeness to the vein quartz and 

 its coarseness readily discriminate it from the earlier quartz. The crystal - 

 outlined hematite and magnetite also help to fill the veins and the spaces 

 between the micaceous hematite laminre between which accommodation 

 took place. The secoudarv material usually fills the spaces entirely, thus 

 completely healing the rock, and because much of the material is arranged 

 parallel to the original lamination the structure is emphasized by the sec- 

 ondary impregnations. 



It has been noted that the jaspilite is chai'acteristic of the uppermost 

 horizon of tlie Iron-bearing formation — that is, it is immediately below the 

 next overlying series. This contact zone was one of the great planes of 

 accommodation, and thus the d^aiaraic effects upon the jasper are explained. 

 Between the jasper horizon and that at which the ferruginous cherts occur 

 is a transition zone. In this the layers of siliceous material sometimes 

 have borders of red, iron-stained quartz. It has been explained that the 

 chief differences between the jaspilites and ferruginous cherts are the blood- 

 red character of the minute hematite pai'ticles and the micaceous character 

 of the ferruginous layers of the former. It appears highly probable, there- 

 fore, that dvnamic action transformed tlie ferruginous chert into the jasper, 

 the layers of earthy hematite being sheared into micaceous liematite, and the 

 inclusions of earthy hematite being changed into the blood-red variety. 



The foregoing general description is of the rocks as they occur in the 

 eastern part of the district. At the west end of the district the predominant 

 varieties of the Negaunee formation are the griinerite-magnetite-schists and 

 the jasper. There are alst) subordinate amounts of ferruginous chert. In 

 this part of the area the rocks are much more coarsel}" crystalline than in 

 the eastern part of the district fPl. XXIII). The quai'tz grains in the 

 extreme western end of the district have diameters averaging from 0.10 to 

 0.15 mm., and in the southwest arm they average about 0.20 to 0.40 mm., 

 and run as high as 1 mm. It will be seen that the size of the grains is 



