318 THE GEOLOGY OF MINNESOTA. 



[Graywacke. Arkose. Slate. 



No. 324. GRAYWACKE. (Fine.) 



From the portage from Oak lake to Otter Track lake, on the United States side. Said to be a condition 

 or variation of rocks Nos. 323 and 311. 



Ref. Annual Report, ix, pages 85, 86. 



Very fine grained and dense, of a slate color, massive (i. e., not sheared), 

 and homogeneous. 



Mir. The section (which is too thick) consists of angular fragments of various 

 minerals, but the most evident is quartz. This is perhaps also the most common. 

 A few similar fragments of a striated feldspar are also observable. These lie in an 

 abundant matrix of translucent grains, which seem to be darkened between crossed 

 nicols by mutual overlapping and by a little chlorite. In a thinner section the clastic 

 origin of the rock is evident. A few grains still give colored polarization. These 

 are in part inuxruvite, and in part epidote. Between crossed nicols the slide is rather 

 dark, except in the areas occupied by the quartz and feldspar grains. 



Two sections. 



Age. Upper Keewatin. 



Remark. The fine debris of which this rock is composed is essentially granitic, 

 and was doubtless derived from the Saganaga granite, on which this series of strata is 

 seen to lie about one-fourth of a mile east of the portage from Oak lake to Saganaga 

 lake. (Compare No. 322; also Nos. 2031-2045.) N. H. w. 



No. 325. ARKOSE. 



East end of Knife lake, on the international boundary, S. E. ^ S. W. % sec. 32, T. 66-6 W. From the slate 

 series of the region which extends from the portage from Saganaga lake to Oak lake. This member is an impor- 

 tant one in the series, as it represents the rock which continues a good part of the distance from the east end of 

 Knife lake, at least to the narrows of the same lake (between sections 11 and 12). The rocks all have a greenish 

 color, but are not always slaty. 



Kef. Annual Report, ix, page 86. 



Meg. A non-slaty, much greener variety of a rock similar to No. 324. 



Mic. This rock is very similar to rock No. 322 and doubtless had the same 

 origin. It is coarser than Nos. 323 or 324. 



Age. Archean (Upper Keewatin). 



Remark. It is an interesting fact that the coarser parts of the Upper Keewatin, 

 about Saganaga lake, are not at the contact on the granite, but at a considerable 

 distance from it. (See Part I.) N. H. w. 



No. 326. SLATE. ( Pyritiferaus. ) 



Ontario; north side of Knife lake, about three-fourths of a mile east of the portage to Maple Leaf lake. 

 (Maple Leaf lake is a small lake, not more than a mile across, lying in Ontario between the north bay, near the 

 west end of Knife lake, and the northward extension of Carp lake; Carp lake is called Pseudomesser lake in the 

 fifteenth and sixteenth annual reports. The usual canoe route between Knife and Carp lakes is through Maple 

 Leaf lake.) 



Ref. Annual Report, ix, pages 86/87. 



