100 THE PENOKEE I1ION-15EAKING SERIES. 



Xi tbt' south vt'iii of the Colby mine tlir ore is limitofl on the south by a com- 

 pact heniatitic slate, which is light-cohned and sandstone-like in places. South of 

 the mine is an outcio]) of siliceous aigillite, which is iuterbedded witli quartzite- 

 schist. 



P>y the laihoad near Bessemer, coniinn; from the Valley mine, is an outcrop of 

 conglomerate, with slight dij) north. It is a small exposure, but in place, composed 

 mostly of i)ebbles of dark led sandstone, lieniatite, graiuilite, and diabase. It* 

 appears like a conglomerate at the base of the Keweenian (p. 186). 



The section at the Aurora mine, in desceinling order, is: Broken and mixed ore. 

 Main deposit of ore dii)i)ing north at an angle of about 65°. Quartzite forming the 

 foot wall in the Colby and Aurora mines. Siliceous argillite south of Colby mine — 

 seen 250 feet; this perhaps occupies part of the concealed space south of the Aurora. 

 Quartzite and syenite gneiss iuterbedded in the hill 633 feet south of the north face 

 of the quartzite in the Aurora; thickness, 595 feet. Syeuite gneiss (502) on the hill 

 south of the Aurora. 



This syenite is a heavy outcrop. It contains some fragments, mostly of green- 

 stone, and only partly rimnded. It reminds me of the Seagull and Saganaga regions, 

 Minnesota. The rock weathers light colored. It is granular and porous, varying to 

 compact. The feldspar is very pale jtinkisli, and the hornblende is grayish greenish. 

 It presents all the characters of true syenite, showing no trace of bedding within the 

 area subject to observation. But it is evidently a fragmental rock, since it contains 

 many rolled fragments. It furnishes us ocular evidence that real syenite, with all its 

 proper crystalline characters, may be a rock of sedimentary origin. 



Looking around, we discover other evidence of its close affinity with products 

 of sedimentary action. Close by, it overlies a true, fine-grained quartzite (503). The 

 contact is apparent in several places. Four rods south of this syenite, a considerable 

 mass of quartzite is imbedded in syenite. Down the hill a few rods farther, we find 

 a vertical ledge of gneiss including warped and broken sheets of a siliceous schist 

 (pp. 186-187). 



The succession in the vicinity of Penokee gap is given. Here at the 

 south is found hornblende-schist and siniihir n)cks 988 feet in thickness, 

 which dip to the south, and then the Penokee series with 3,480 feet of 

 strata dipping to the north, including, from south to north, vitreous quartzite, 

 siliceous slates, raagnetitic slates, and argillites. 



The firmly accepted conclusion of the Wisconsin geoh)gists in reference to the 

 equivalency of the magnetitic and carbonaceous slates of the Penokee gap makes 

 them a continuation of the heniatitic schists of the Gogebic range. That is, they hold 

 the formation in both regions to be Huronian. That tlic Gogebic iron-bearing strata 

 are uot Huronian, I feel prepared to affirm. And 1 can not resist serious doubts of 



