CHAPTER VI. 



By (J. R. Van Hise. 



THE UPPER SLATE MEMBER. 



Section I. Details. 



Natae autl basis of separation. Transition from Iron-beaiint; to Upper slate member. Geograpliieal 

 distribution. Topographical features. General jietrograpliical character. Petrograpbiial 

 characters of tlie four types of rock. Tabulation of iietroijraphieal observations. 



Section II. Origin of the Upper slate rocks. 



(1) Quartzose graywacke. (2) Mnscovitic and biotitic graywacke. (3) Biotitic graywaeke. 

 (4) Mnseoviti/5 biotite-slate. (.5) Nearly crystalline mnscovitic liiotite-schist. (H) Crystalline 

 mnscovitic biotite-schist. Black mica-slates. Sonne of material. 8nmmary. 



SECTION I —DETAILS. 



Name and hasis of separation. — All the rocks of the Penokee series above 

 the Iron-bearing member are placed together, althougli their thickness is 

 for a distance of many miles several times as great as the three lower forma- 

 tions of the series combined. Lithologieally tlie great mass of the rocks 

 are slates. Frequently the slate becomes somewhat lllassi^•e and occa- 

 sionally l)ecomes a qnartzite ; also in certain localities it becomes quite 

 schistose; but all these jjhases may ])e said to he exceptional. It is not 

 meant to imply by the term "slate" that aii}' of the rocks have a slaty 

 cleavage. The direction of the easiest parting and bedding alwa)'s corre- 

 spond, and none of the rocks possess the uniformity of composition and part- 

 ing requisite! for roofing slates. The formation is given the name "Upper 

 slate member," which at once sliows its stratigrapliical position ;ind litliolog- 

 ical character, and distinguishes it from the Quartz-slate member, which 

 is below the Iron-bearing member. 



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