550 THE MARQUETTE IROjST-BEAEING DISTRICT, 



below the upper quartzite, with which they are frequently directly iu con- 

 tact. More commonly, however, the rich ore is separated from the quartzite 

 by a small tliickuess of black-ore jasper or mixed magnetite and quartz, 

 usually banded, or sometimes by soaprock, while immediately beneath and 

 continuous with the rich magnetic ore specular ore is sometimes found. 

 Soaprock usually, and iu the case of all the larger bodies invainably, forms 

 the foot wall. The magnetite deposits are mostly confined to the eastern 

 and middle subordinate svnclines, but are also foi;nd of small tliickness in 

 dejjth along the straight eastern limb of the main fold 



The specular hematite or slate-ore bodies occur both in the contact 

 zone and below it, entirely within the specular jasper. (PI. XXXR^, fig. 1.) 

 As a rule the deposits of the contact zone contain the richest ore, wluch is 

 characterized by the large size of the indi^^dual crystalline plates. As a 

 deposit is followed back from the contact zone into the jasper, these plates 

 become progressively smaller, and at the same time the ore grows more 

 siliceous. The larger deposits of specular ore are associated -with soaprock, 

 which may bound a deposit either on the foot or the hanging wall side. 



The deposits of specular ore that occur along the straight eastern limb 

 of the fold all show a well-marked pitch toward the north, in the general 

 direction of pitch of the main fold, but at a very much higher angle. 

 These bodies all lie in the contact zone at the surface, having the upper 

 quartzite on the hanging wall. As they are followed in depth they are 

 found to recede from the quartzite, and to follow the banding of the uuder- 

 Iving jaspers, which dip at a higher angle than the quartzite. They 

 terminate in depth entirely within the specular jasper. As one body departs 

 from the quartzite and becomes entirely inclosed by the jasper another 

 frequently comes in above it in the contact zone. 



The deposits in the subordinate synclines in the horseshoe turn have 

 not shared the intense crumpling to which the specular jaspers have been 

 subjected. They occur in thin, unwai-ped sheets, which start with one edge 

 in the contact zone, having the upper quartzite on the hanging wall and 

 set back from it parallel with the local strike of the closely folded jaspers. 

 The longest dimension thus follows down the contact, pitcliiug with the 

 dip of the quartzite, while the longer of the two horizontal dimensions is 



