330 



THE MAEQUETTE IRON-BEAEING DISTRICT, 



the intrusives find the iron formation may lie in the exceeding brittleness 

 of the hitter. When the series was folded this formation was fractured at 

 innumerable ])hices, thus allowing the wedges of igneous material to enter. 



At a few places the tuffaceous igneous rocks occur, giving evidence of 

 contemj)oraneous volcanic activity. 



In the mapping only those areas are coloi-ed as greenstone Avhich are 

 shown b}' ^•isil)le exposure or by underground working to be igneous. 

 There can l)e no doubt that greenstone, in the forms of bosses and dikes, 

 occupies a considerable area which is given the color of the Negaunee iron 



Fig. 17.— Intrusive jrreenstone in grUnerite-m.agnetite-sr^hist, from near center of sec. 12, T. 47 N., K. 29 "W. 



formation, l)ut the jiositions of such greenstones are undetermined. There- 

 fore the iron-form;ition color covei's both the iron formation proper and 

 unknow^i areas of included greenstones. 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



The largest area of the iron formation (Atlas Sheet IV) occupies the 

 major part of the E. h of T. 47 N., R. 27 W., and the W. h of T. 47 N., 

 R. 26 W., extending from near Tenl Lake on the north to the village ot 

 Palmer and to Summit Mountain on tlie south. From the southern })art 

 of this broad central area two arms project to the northeast and east. 

 The first arm runs in a northeast direction from Palmer, sjireads out into a 

 broad area in sees. 10 and 15, T. 47 N., R. 20 W., and terminates in sec. 3; 

 the second arm, a half to three-quarters of a mile Avide, extends east from 

 Palmer to the sand plain in sec. 27, T. 47 N., R. 2(3 W. Its course after 

 reaching the sand jilain is undetermined. From the broad Ishpeining- 

 Negaunee area two arms pass to the west, one near the south side of the 

 Marquette series and the other near the north side. The southern belt has 



