GRANITIZATION OF ACIDIC LOWER HURONIAN SCHISTS 239 



influence generally exercised by the granite, cutting the iron forma- 

 tion in the Pucaswa area, stands in very marked contrast. For 

 instance, the iron formation there is intruded by a huge granitic 

 batholith on the eastern branch of the Pucaswa River, about four 

 miles above its confluence with the western branch. The eruptive 

 contact is abrupt and decided, but the iron formation, which consists of 

 banded magnetic chert, is relatively practically unaltered. The granite 

 is bright red and somewhat coarse-grained, though of even texture. 



Visible contacts between the Upper Huronian and the intruding 

 granites are rare as compared with those with the Lower Huronian. 

 This is due probably to the much smaller surface area occupied by 

 the Upper Huronian rocks. There is a good contact showing dis- 

 tinctly the eruptive relations of the granite on the southern shore of 

 Lake Charlotte. Another is on the western shore of Western Lake 

 Kabenung, and still another, and one which is perhaps better shown 

 than either of the others just given, on the shore of Lake Superior, 

 near the mouth of the Dore River. 



Somewhat interesting is the geologic section exhibited along the 

 Lake Superior shore from Otter Head eastward. Here the ceaseless 

 washing of the waters has kept the rocks well exposed, and the 

 relations existing between the different formations is easily observed. 

 At Otter Head the rocks, named in order of their age, consist of small 

 areas of evenly banded gneiss, ordinary light-reddish granite, coarse- 

 grained pegmatite, quartz and calcite veins, and dykes of basic 

 igneous rocks. The gneiss is composed of alternating bands one- 

 quarter of an inch and less in width, of dark-colored minerals, chiefly 

 biotite, and similar bands of light-colored minerals, chiefly orthoclase, 

 oligoclase, and quartz. There is apparently not much differentiation 

 into laminae of the felspar minerals and quartz. The light-reddish 

 granite, which is the prevailing rock, is exactly similar to the Post- 

 Huronian granite described above. The pegmatite, consisting chiefly 

 of large individuals of microcline, orthoclase, plagioclase, quartz, 

 and biotite was probably formed as the result of the action of steam 

 acting upon the hot granitic magma, either during or immediately 

 following its intrusion. The veins are later than either granite or 

 pegmatite, but probably owe their origin to the circulating thermal 

 waters, which followed, and were the result of, the granitic intrusion. 



