900 THE GEOLOGY OP MINNESOTA. 



[Slate. Graywacke. 



not been so completely transformed, molecularly, as to have lost their original shapes. 

 Another variation consists in the occurrence of occasional irregular bands of much 

 finer materials. One is quite marked. It transmits but little light between the 

 nicols owing to the overlapping refraction, but is no less transparent than the adja- 

 cent rock. It evidently consists of the same minerals in finer comminution, quartz 

 being evident. One section. 



Age. Upper Keewatin. 



Remark. This rock was collected as a possible gray slate, with a view to repre- 

 senting the clastic end of a gradation to the granite of the region. It is very evident 

 that it is now in the form of a regenerated fine debris such as could be produced at 

 first in rather quiet water. It seems to have been affected by the same process as 

 that which has passed over the coarser debris, giving it a secondary crystalline bond. 



Dr. Grant's note is as follows: " Here there is a gradual change from a gray 

 aphanitic rock much resembling some of the gray slate of the vicinity to the pyrox- 

 ene granite as represented by Nos. 556G and 557G. The gray rock, however, shows 

 no evidence of lamination or any definite slaty cleavage; it may be a very fine-grained 

 facies of the granite in which the porphyritic feldspars are lacking. As yet these 

 specimens have not been studied microscopically. Nos. 601G to 615G represent this 







gradation. No. 601G is the gray rock. The specimens up to No. 612G were taken 

 within distances of one to four feet, going eastward from No. 601G. Nos. 613G, 

 614G and 615G occurred thirty or forty feet further east, and there pass into the 

 facies of the granite represented by Nos. 556G and 557G." N. H. w. 



No. 602G. SLATE. (Metamorphosed.) 



Same place as No. 601G, but further east. 



Ref. Annual Report, xx, page 72 ; Annual Report, xxi, pages 37, 51. 



Meg. Quite similar to the last, but with greenish shadings in which evidently 

 epidote is more abundant. 



Mic. Same as the last, but with fewer of the coarser feldspars. There is also 

 occasionally a fine alternation of epidote with the rest of the rock, producing a micro- 

 scopic, banding-like schistosity. One section. 



Age. Upper Keewatin. N. H. w. 



No. 603G. GRAYWACKE. (Fine, metamvrphoxed. ) 



Same place as the last ; a little further to the east. 



Ref. Annual Report, xx, page 72 ; Annual Report, xxi, pages, 37, 51. 



Meg. Appearing much like the last two, but evidently of coarser grain, showing 

 an occasional cleavage reflection of feldspar. 



Mic. Hornblende appears more evident as a constituent of the dark (and 

 greenish) element of the rock. The coarser feldspars are fragmentary, and some of 



