Great Lake Basins of the St. Lawrence. 259 
Lake Nepigon country may be explained by that lake now 
occupying the crater of an ancient volcano, and he is in- 
clined to take the same view of Lake Superior. Whatever 
may be said of Lake Nepigon, the features of the present 
floor of Lake Superior hardly bear out this conclusion, 
although there can be no question of the existence of enor- 
mous volcanic forces at ditferent points. 
Whilst the history of Lake Superior, during the vast ages 
which have elapsed between the Cambrian period and the 
close of the Tertiary, is in most respects a complete blank, 
yet, from the latter time, its history begins once more. 
Apart from the facts which the superficial deposits supply, 
some reference to which will hereafter arise in connection 
with the other lakes, the fauna of the lake itself and the 
flora now existing around its shores afford some interesting 
chapters. 
. On the jutting headlands of the lake, and along the shores 
of the bays of its northern coasts, there are both subarctic ; 
and boreal plants which appear to form a completely iso- | 
lated group in these localities. Their original presence, 
there, it is difficult to disassociate from a migration before | 
the close of the glacial era, when, with the somewhat colder | 
climate, and under the influence of the low equable temper- 
ature of the great inland sea south of the glacier-clad Lau- / 
rentian and Huronian mountains, subarctic and _ boreal 
plants found a natural highway along the coasts. With | 
lofty mountains to the immediate northward, such plants, 
as well as perhaps arctic species, were doubtless not un- 
common. As the waters receded and the climate became i 
milder, these northern plants were driven to localities like | 
the headlands of Lake Superior, where the low temperature 
and moist atmosphere were favorable to the continuance of 
some of them in a struggle for life, in which probably most 
became extinct. 
The inland maritime plants of Canada, which occur along 
the coasts of all the Great Lakes, and on saline ground in 
New York State, and far westward, appear to be the rem- 
nants of a larger maritime flora which margined the coast 
ete 
