426 LAKE SUPERIOR. 



The collections I have made of these rocks are sufficiently exten- 

 sive to affi)rd materials for such an illustration, and I may, perhaps, 

 on another occasion, publish a more detailed account of the geological 

 features of the northern shores, unless the expected publication of 

 the geological survey of Canada by Mr. Logan, renders this essay 

 superfluous. 



I would here acknowledge the benefit I have derived in my in- 

 vestigations from the published reports of this survey, and also from 

 the verbal communications of Mr. McLeod of Sault St. Marie. The 

 rocks which occur on the northern shores are so characteristic that 

 they cannot be mistaken, and even should the materials which I 

 have collected not be published more in full, they will at all events 

 aflbrd to those who study the geological distribution of erratic bould- 

 ers, valuable means of comparison, which will show that most of the 

 erratics which occur in the northern parts of the United States are 

 derived from the primitive range extending north of the lakes reach- 

 ing along Canada and the United States to the Atlantic Ocean. 



Among these rocks there is a variety of deep red felspar por- 

 phyry speckled with epidote, which, from its brilliant color, partic- 

 ularly attracts attention, and which occurs all along the northern 

 shore from the Pic to Thunder Bay. This variety I have not 

 observed farther east, and it may perhaps be taken as a guide to 

 ascertain the range of erratics derived from the northern shore of 

 Lake Superior. 



