332 THE GEOLOGY OF MINNESOTA. 



[Tuff. 



i', epidote, feldspar, quartz, isotropic (chloritic?) substance, and is similar to 

 the next. 



Two sections. 



Age. Archean (Kawishiwin of the Lower Keewatin). N. H. w. 



No. 356. TUFF(?) ("Greenstone.") 



Kawashachong falls, forming the brink, and the bluffs below the falls; south side sec. 17, T. 63-11 W. 



Ref. Annual Report, is, page 92; Annual Report, x, pages 89, 95; Annual Report, xv, page 319; Annual 

 Report, xix, pages 126, 127; Bulletin ii, page 123; Bulletin vi, pages 37-40, 420. This is also the same rock as 

 Nos. 997, 998, 999 and 138 (W.). 



Meg. Appears similar to the rock at Pipestone rapids. It contains narrow, 

 white quartz veins and deposits, some of which are two or three feet wide. This 

 rock is neither bedded, jointed nor distinctly schistose, but it breaks in a very coarsely 

 schistose manner, and each piece runs to blunt points lenticularly. Chlorite perme- 

 ates and colors it. It seems to be closely seamed in all directions, but not with any 

 regularity, if we except the general schistoid fracture, which coincides with the 

 slates in being nearly perpendicular, and yet in sloping to the south. It abounds in 

 talcose(?) or chloritic and hematitic slickensides. It is everywhere rough super- 

 ficially and mashes under the hammer before breaking, and then breaks toughly and 

 roughly. 



Mic. The sections do not show any schistosity, but that may be owing to 

 being parallel to the structure. That the rock is fragmental is evident, as remarked 

 by Wadsworth, and it has undergone not very much deformation since its deposition. 

 . Along with a few fragments of triclinic (probably secondary) feldspar and much 

 clinochlore, indicating a basic source for the ejection which supplied the materials of 

 this rock, are numerous quartzes which, also, to some extent, have been enlarged 

 so as to embrace the surrounding rock material. The chloritic element is sometimes 

 pennine, and is sometimes also isotropic. A considerable amount of the green color 

 of the rock is also due to the presence of hornblende which appears in the thin section 

 with higher double refraction than any other mineral. This mineral is sometimes in 

 large grains with reeded extremities, but occurs in some places quite abundantly as 

 finer grains and fibres. Its alteration is to clinochlore and to an isotropic chloritic 

 substance. Culcite is common, as is also agray, leucoxene-like substance. Hematite and 

 pyrite are rarely seen. Magnetite is questionable. 



Two sections. 



Age. Archean (Kawishiwin of the Lower Keewatin). 



Remark. The hornblende in this rock has a very varied aspect, and it is often 

 difficult to distinguish the finer grains from epidote. Their index of refraction is 

 sufficiently near that of epidote and the overlapping produces a darkness that likens 

 the aggregate to the obscure upper colors of the third order as required by epidote of 



