286 THE GEOLOGY OF MINNESOTA. 



[Quartzyte. Diabase. 



No. 259. QUARTZYTE. ( Gray. ) 



From the east side of Hat point, underlying or cut by the rock No. 258, forming a part of the slate for- 

 mation at Grand Portage. 



Compare Nos. 257, 270. 



Ref. Annual Report, ix, page 62. 



Meg. This rock is largely composed of <jn<oiz in sub-angular grains with an 

 occasional fragment of phtf/inr/tixc. the cement being of smaller grains of the same and 

 of feldspathic (?) material and of mica; occasionally a grain appears to consist of 

 much kaolinized feldspar, but still charged with impregnations of iron oxide. 



This rock is illustrated by several other numbers, which afford better facilities 

 for description. It contains globular masses or colored spots which, on a fractured 

 surface, give the rock a spotted aspect, the spots being lighter than the rock in 

 general, and often reddish. These reddish spots consist apparently of the indigenous 

 elements stained at their borders by an accumulation of ferric oxide which here per- 

 meates the feldspars. A thin section, made so as to cut one of these spots, appears 

 to have a different matrix for the quartz grains, consisting largely of calcite. This 

 calcite is in crystals which embrace, under one orientation, many of the grains of 

 the sandstone. Throughout the rest of the rock no calcite is seen, but the section is 

 singularly dark between crossed nicols, as if it contained considerable devitrified 

 glass. 



Two sections. 



Age. Animikie. N. H. w. 



No. 260. DIABASE (with olivine). 



Near the head of Wauswaugoning bay. From a dike cutting the Animikie slates and quartzytes, and 

 running S. 45 W. 



Ref. Annual Report, ix, page 62; Bulletin ii, pages 115, 116. 



Meg. A compact, heavy, dark-gray diabase of medium grain. 



Mic. A diabase composed of plagiodnse laths, aitgite, olirini- and nidt/in'tifi-. The 

 rock has been considerably altered. The olivine is all replaced by a brown material 

 (bovlui/jiti- ?). The feldspar is also altered, and the section has much dirty greenish 

 chloritic material and some magnetite, hornblende and a little biotite, all of which 

 seem to be alteration products from the augite. The augite is light violet brown in 

 color and some of it is slightly pleochroic, varying from the usual color to a pale 

 straw color. 



Two sections. 



Age. Cabotian. u. s. G. 



No. 261. DIABASE (urith olivine). 



From the summit of the hill on N. E. ]4 sec. 25, T. 64-7 E. Northeast of the head of Wauswaugoning 

 bay. Represents the rocks of the hills about Grand Portage. 



Ref. Annual Report, ix, pages 63, 66, 70; Bulletin ii, page 106; American Association for the Advance- 

 ment of Science, vol. xxx, page 163. 



