344 THE PENOKEE IRON-BEARIXG SERIES. 



gnulual chiinye in tlie nature of the orig-inal material of the Up^jer shite, 

 it becoming more and more strongU' fehlspathic ; west of Bad river prac- 

 tical!}' all of it wa8 feldspar of an acid character. By reference to 

 chapter i it will he seen tliat the Western granite, which reaches the 

 newer series in the vicinity of Penokee gap, extends west and south for a 

 long distance. The granite contains an unusually small quantity of quai'tz, 

 being either a true syenite or a granite in which the quartz is usually not abun- 

 dant There is clearly a connection between the character of this part of the 

 Upper slate and the underlying rock. Tlie degradation of the latter, accom- 

 panied by natural sorting, has furnished the nearly pure feldspar material 

 •which originally constituted the Upper-slate member and made it of such a 

 composition that it was possible by metasomatic processes to pi"t)duce from 

 it a tine grained crystalline mica-schist. 



Summari/. — 1. The rocks of the Upper-slate meihber are mechanical 

 sediments, which have been everywhere altered to a greater or less extent 

 by metasomatic changes, and at times the alterations have extended so far 

 as to produce crystalline schists. 



2. In general, the eastern part of the formation is less altered than the 

 western part. Here the prevailing rocks are clay-slates, graywackes, and 

 graywacke-slates. In jiassing to the westward the rocks become more 

 crystalline in character, and at the extreme west end only mica-slates and 

 mica-schists are found. 



3. While this is true in a general way, in the same vertical section 

 there may be found all phases of the transformation from completely frag- 

 mental rocks to crystalline schists. As far east as Sec. 14, T. 46 N., 

 R. 2 K., Wisconsin, a rock which is verv close to a crystalline schist is 

 found. At the Penokee gap section the most completely fragmental gray- 

 wacke of the whole memlier occurs, and in this section there are all o-rada- 

 tions to that but one degree removed from the most crystalline phases 

 found in the formation. Even in a single exposure in this section are found 

 plainly fragmental graywackes and mica-slates, and micaceous graywackes 

 which approach very close to a mica-schist. 



4. The parts of the U])per slate wliich have received large fragmental 

 particles of quartz are those in whicli the clastic character is easiest to rec- 



