ICE FURROWS ON THE LAURENTIDES. 



245 



GROOVED, SCRATCHED, AND POLISHED ROCKS. 



Instances of the action of ice in abrading and polish- 

 ing extensive surfaces of rock are very numerous on the 

 Laurentides between Lake Superior and Lake Winnipeg. 

 The first wide expanse observed on the west side of the 

 water-shed is at Baril Portage, 143 miles from Lake 

 Superior, and 1500 feet above the sea. Where an arm 

 of Mille Lacs approaches this portage, gneissoid hills 

 and islands about 100 feet high show a well defined 

 stratification dipping north, at an angle of about 15°, and 

 on that side smooth, and sometimes roughly polished ; on 

 the south side they are precipitous and abrupt. The 

 same character is observed on the portage itself ; the north- 

 eastern exposures of the rocks there are smooth and 

 striated, the southern rugged and often precipitous. 



On Sturgeon Lake 208 miles from Lake Superior and 

 1156 feet above the sea, the north-eastern extremities of 

 hill ranges slope to the water's edge, and when bare are 

 always found to be evenly smoothed and ground clown. 

 The aspect of the south and south-western exposures is 

 that of precipitous escarpments. 



On a small island about twenty-five miles north of Garden 

 Island, Lake of the Woods, there is a remarkable exposure 

 of greenstone conglomerate, nearly on a level with the 

 water of the lake. The surface • of the rock is almost 

 horizontal, beautifully polished, and strongly marked with 

 glacial furrows and scratches. The direction of the furrows 

 is N. 25° E., they are all parallel to one another, some of 

 them half an inch in depth, and nearly double that measure 

 in width. They pursue a uniform direction for many 

 yards until concealed by the bushes which fringe the 

 bare rock some forty or fifty feet from the water's edge. 



R 3 



