720 THE GEOLOGY OF MINNESOTA. 



[Greenwacke. 



This rock again connects the granite petrographically with the rock No. 1409, 

 the peculiar pebbly green schist of the region. Another section from No. 1410 shows 

 characters of the hornblendic schist of the region without feldspars. 



Remark 2. Owing to the important bearing of this rock section on the 

 hypothesis of the generation of the granite of Kekequabic lake from metamorphism 

 of the schist of the region, still another section was made of the rock No. 1410; and 

 as this section is entirely of the character of the second slide above mentioned, being 

 a hornblendic schist similar to rocks Nos. 1409 and 1411, from the same island, it is 

 to be inferred that the rock above described as No. 1410 did not come from the top 

 of this island, but from some part of the granitic rock of the region, an error being 

 made in giving it this number; and hence that it does not prove such selective 

 distribution of metamorphism on this island as above presumed. 



It is deemed best to allow the foregoing description to stand with this correction, 

 inasmuch as this idea of selective metamorphism along certain strata rather than 

 others has since been published (American Geologist xxii, November, 1898, page 

 308), based on this thin section, and since, although here there is no warrant for the 

 inference, it is a feature that is likely to be produced in the clastic rocks under the 

 process of metamorphism which here is supposed to have taken place. Three sections. 



N. H. W. 



No. 1411. GREENWACKE. (Pebbly.) 



Prom the middle of the south cliff of the same island. 

 Ref. Annual Report, xvi, pages 103, 105, 125. 



Meg. More siliceous, showing sedimentary banding. 



Mic. This rock is like No. 1409. Besides the pebbly spaces occupied by micro- 

 granulitic structure, there are others which were once apparently feldspars which 

 have lost their integrity and are now charged with the same kind of secondary grains, 

 being revealed only by a faint extinction that supervenes four times over the grain 

 in one revolution. One section. 



Age. Archean (Upper Keewatin). N. H. w. 



No. 1412. GREENWACKE. 



The same as No. 1411, near the water, having boulders of rock like itself ; Kekequabic lake. 

 Ref. Annual Report, xvi, pages 103, 105, 125: 



Meg. Green, but having lumps of harder rock. 



Mic. This rock is like No. 1409 in nearly all respects. The hornblendes show the 

 forms of the original augite grains in the existence of the darker central areas. The 

 surrounding fine interlocking matrix shows variations of size of grain, indicating 

 transformations from a more coarse f eldspathic (though clastic) condition. One section. 



Age. Archean (Upper Keewatin). N. H. w. 



