1898-99. | THE GEOLOGICAL HISTORY OF LAKE SUPERIOR. 45 
THeAGEOLOGICAL HISTCGRY OF LAKE.SUPERIOR: 
By Dr. ROBERT BELL, F.R.S. 
(Read April 15th, 1899.) 
In the talk which I am about to give on the Geological History 
of Lake Superior I propose to endeavour to trace the origin and develop- 
ment of the lake itself rather than to sketch the geology of the surround- 
ing country. The genesis of some of the great lakes, or rather of the 
depressions in the continent which they occupy, has been the subject of 
some investigation and of much discussion and speculation among 
geologists, but their researches and controversies have related mostly to 
the lower lakes, while but little has yet been written as to the geological 
history of Lake Superior. It was on this account, and because I have 
worked for many years on and around this inland sea and have paid 
some attention to this matter, that I have chosen it as the subject of my 
address to-night. 
Before proceeding to speak of the basin of Lake Superior, I shall say 
a few words about the basins of the other great lakes, the origin of each 
of which has been similar to the others, but in some respects different 
from that of Lake Superior. Sir Andrew Ramsay and Sir William 
Logan supposed them to be due principally to glacial action; that is to 
say, that they had been scooped out of the rocks in which they lie, 
mainly by the denuding force of heavy and extensive masses of land 
ice. Although the eroding or excavating power of thick glaciers is 
very great, still it does not appear to have been sufficiently powerful to 
account for all that was formerly attributed to it. It has been pretty 
satisfactorily shown that during the glacial period their action in modify- 
ing the surface features consisted largely in the transportation of pre- 
viously decomposed and loosened rock. 
A former assistant of mine on the Geological Survey, Dr. J. W. Spencer, 
was, I think, the first to point out that the depressions now occupied by 
all the lakes east of Lake Superior represent the wide valleys or hydro- 
graphic basins of former rivers, more or less modified by subsequent 
glacial action, together with slight and widespread undulations or warp- 
ings of the crust of the earth. Although our lakes are so extensive 
