380 A. WINCHELL — RESULTS OF A.RCHEAN STUDIES. 



this conglomerate are derived from crystalline rocks, being largely granu- 

 litic, gneissic, and quartzose, and they lie imbedded bo firmly that fractures 

 of the rock pass equally through them and the matrix. This matrix gen- 

 erally is a g 1. but often Biliceous, argillite, dark, or inclining to greenish, 



with cleavage coincident with tin- sedimentary bedding 



No other occurrence of the < tgishke conglomerate is at present known in 

 Minnesota, but Dr. Lawson has Bhowa that it recurs on Rainy lake, at Ral 

 Rool bay, and also on Grassy and Shoal lakes,* where similar pebbles are 

 imbedded in a fissile, glossy, green, chloritic schist. Seventy-live miles north- 

 east oft >gishke-muncie lake, in the vicinity ofThunder hay on Lake Superior, 



cur vertically-standing conglomerates of exceedingly similar character. 

 I quote from the Report of Sir William E. Logan: 



"Rising in the series [superjacent to the gneisses] the dark-green slates become 

 interst ratified with layers holding a sufficient number of pebbles of different kinds 

 to .•.institute conglomerates. The pebbles appear to be all derived from altered rocks. 

 They vary greatly in size in different places and occasionally measure a t'""t in 



diameter. Where the slate conglomerates have I n worn by the action of water, the 



pebbles are generally worn down equally with the rest of the surface, and, though a 

 very distinct picture of them is presented on Buch a surface, * * * it yet often 

 happens, unless the pebbles are of white 'mart/,, that they are very obscurely dis- 

 tinguishable on fracturing the reek, both the pebbles and the matrix having a gray 

 . showing very little apparent difference in mineral character. * * The 



mck has nowhere on the lake hern observed to display true slaty cleavage independent 

 of the bedding." f 



These are characters of the ( )^ishke conglomerate. The only difference 



is a re greenish color of the slates. The same conglomerate is exposed at 



other points on the shore of Lake Superior. A voluminous outcrop is noted 

 at the month of the River Don', where seventeen hundred feet are described 

 as green slate rock in vertical attitude, striking ea-t and west and presenting 

 sometimes ribboned edges of green, black, red. and -ray and mostly charged 

 with crystalline pebbles and bowlders firmly imbedded. "Toward thelower 

 part it assumes more the character of the gneiss which usually succeeds it." 



In the region of Pog lake, north of Thunder hay, the slate- which else- 

 where are greenish and conglomeratic are described as "dark greenish blue 

 or greenish Mack slate-, passing downward almost imperceptibly into a horn- 

 blendic gneiss. 



I direct particular attention to this east ward extension of dark and green- 

 ish Blates, di H-' ly conglomeratic, at intervals, as far as the eastern shore of 

 Lake Superior. 



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186 '•. pp ' l 



