102 THE PENOKEE lEON-BEAKING SERIES. 



ite by perfectly sharp lines, and their intrusive character is unmistakable. 

 The granite is described as at once an eruptive rock and a conglomerate. 

 This description is doubtless due to the fact that in the granite are dark 

 colored obscure roundisli areas which have a pseiido-fragmental appear- 

 ance. These areas, composed largely of dark-colored minerals, are very 

 common in the ancient granites of the Noilhwest and may be either actual 

 fragments of the more ancient crystalline schists wliich have been caught 

 in the granite at the time of its eruption and only partially absorbed, or 

 they may represent segregations. The north face of the granite ledge is 

 brecciated to a cei'tain degree and its joints are filled with cherty and sili- 

 ceous slates belonging to the base of the Penokee series. The granite 

 surface is plainly one of erosion, and there is absolutely no evidence that 

 the granite has been plastic subsequent to the formation of the slate. 

 The phenomena are precisely tliose that are always present when a frac- 

 tured and jointed granite constitutes the surfixce upon which a fragmental 

 slate formation begins to be deposited. 



If the above observations are correct. Prof. N. H. Winchell's conclu- 

 sions that the granite acts the role of an eruptive rock, l)ut was originally 

 a conglomerate which flowed over the sedimentar}' strata, and that tlie 

 granite is not of Laurentian age but is younger than the Animikie slates, 

 are eiToneous. 



Van Hise (C. E.). The Iron Ores of the Penokee-Gogebic Series of Michigan 

 and Wiscou.sin. Am. Jour. Sci., 3d series, lS8tt, vol. xxxvii, pp. 32-48. 



This article is a condensed advance account of what is contained in 

 the present volume with reference to the position of the ore-lxMlies in the 

 Iron-bearing meinlier and their genesis. As the subject is ti'eated fully 

 in a subsequent chapter, an abstract of this paper will not here be given. 



