1867.] MACFARLANE — GEOLOGY OF LAKE SUPERIOR. 177 



southern sections of the County of Renfrew. To the species cited 

 might be added Saxifraga Aizoon Jacq., Viburnum pnuc iflorum 

 Pylaie, Aster grominifolius Pursh, Vacdnium Vitis-Idcea Linn., 

 Primula farirtosa Linn., P. Mistassinica Michx., Comandra 

 livida Richards., Tofieldia palustris Hudson, Carex Vahlii 

 Schk., Aspidium fragrans Swartz, and many others. I have 

 already suggested the probability that the composition of the soil 

 may, to some extent, affect the range of one of these plants, and 

 it is just possible that the distribution of a few others may be 

 modified by the same cause. It is, however, an observable fact 

 that whilst none of these plants is arctic or perhaps even sub-arctic 

 in its aspect, all have a high northern range. In the United 

 States their distribution is limited to northern New England and 

 Wisconsin, or to mountain sides and summits. The vicinity of the 

 lakes and the broad waters of the St. Lawrence, and their equaliz- 

 ing effects upon the temperature, account in part for the presence 

 of the more boreal forms, and their general northern range for 

 that of others. The little Primulas occur on the American shores 

 of Lakes Huron and St. Clair, but probably the winds, and especi- 

 ally the currents, have brought their seeds from the Manitoulin 

 Islands and the upper shores of the former lake, where both species 

 have been frequently met with by Dr. John Bell. It may be men- 

 tioned that in the St. Clair River, especially where the waters of 

 Lake Huron enter it, the current is very considerable. 



Montreal, April, 1867. 



ON THE GEOLOGICAL FORMATIONS OF LAKE 

 SUPERIOR. 



By Thomas Hacfarlane. 



The crystalline rocks of Lake Superior present many features 

 of interest to the lithologist, and to the student of primary 

 geology ; and the sedimentary rocks of that region, being almost 

 destitute of organic remains, have been the subject of much 

 discussion among scientific men, which can, nevertheless, scarcely 

 be said to have settled unequivocally the question of their age. 

 Having, as I believe, observed certain new facts concerning the 

 composition and association of these rocks, which aie calculated to 

 Vol. III. M ]S T o. 3 



