826 THE GEOLOGY OF MINNESOTA. 



[Graywacke. Tuff. 



No. 2026. GRAYWACKE. 



Stuntz island, Vermilion lake. 

 Ref. Annual Report,, xxiv, page 15. 



Mry. Pebble from the conglomerate, lying in contact with No. 2027. 



Mic. This rock is like that numbered 2016, and the description need not be 

 repeated. One section. 



Age. Pebble in Upper Keewatin. 



licnutrl;. This being a pebble in the Stuntz Island conglomerate, and itself 

 apparently a clastic rock, is an indication that the Stuntz Island conglomerate is 

 nonconformable on some graywackes. N. H. w. 



No. 2027. GRAYWACKE. 



Stuntz island, Vermilion lake. 

 Ref. Annual Report, xxiv, page 15. 



Mc</. Pebble lying in contact with No. 2026. 



Mic. This pebble is a graywacke and consists almost entirely of distinct coarse 

 fragments of feldspar of different kinds and of quartz, the cement between them being 

 calcite and seridtc, with less of the debris that appears in the graywacke on the point 

 in section twenty, which is simply a downward gradation in size of grains like the 

 coarser fragments. In that respect it is like No. 2026. One section. 



Aye. Pebble in Upper Keewatin. N. H. w. 



No. 2030 | . TUFF. 



On the International boundary, at the ridge over which the trail passes between Otter Track and Oak lakes. 

 Ref. Annual Report, xxiv, page 18. 



Meg. Green, coarse, appearing somewhat like a graywacke. This ridge 

 prevents Hunter's island from being an island. It is apparently only a variation of 

 the rock that forms the shores of Knife lake and Otter Track lake, but differs from 

 ordinary graywacke. 



Mic. This interesting rock has an alliance with the tuffs of Kekequabic lake, 

 but it is more characteristically a tuff than any yet seen from that region. It 

 contains large pieces (microscopic) of zirkelyte, in which, however, are idiomorphic 

 crystals of green hornblende, faintly zoned by a narrow rim visible occasionally, and 

 of pyroxene. Throughout the slide, in which is also much zirkelyte, are isolated 

 pyroxenes (augite) and quartzes, and occasionally an area of feldspar in which there 

 is plainly a coarse fibrous and radiated structure, the elongation being negative, 

 i. e., parallel to .. There are also sub-round masses apparently of diabase porphy- 

 ryte in which the little feldspars stand in divergent positions. One section. 



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



