164 Canadian Record of Science. 
They all lie between the Archean rocks and the newer 
strata dipping away from them. The glaciers of former 
times descending from the higher grounds of the former 
against the upturned edges of the softer rocks, tore them 
up rapidly and carried away the debris, thus leaving the 
lake basins. But when the glaciers moved from the strata 
lying upon the Archzan nucleus so as not to tear their 
edges, then no channels or basins were excavated. 
Lakes Hrie, Huron, Michigan, Manitoba and Winnipegosis 
lie in basins worn out of soft strata, dipping at low angles, 
with harder beds above and below them, which form their 
margins. 
The lake region of North America was almost a conti- 
nental plain but little elevated above the sea, and hence 
some of our great lakes lie on or near the water-sheds,. 
Lake Superior is near the highest part of this plain, and 
the water flows from near its margins to the west, north 
and south, and its outlet is to the east. By a small artifi- 
cial cut at Chicago, Lake Michigan discharges into the 
Mississippi as well as the St. Lawrence, and Lake Huron is 
on the same level. 
Dr. Bell next pointed out the important part played by 
dykes of greenstone, etc., in producing the original cuts 
which, by the decay and erosion of the rocks, form the 
channels of rivers, arms of lakes and fiords on the sea 
coasts. Parallel faults or dislocations have the same effect, 
Other river channels, such as those of the northern branches 
of the Ottawa between Mattawa and Montreal, are excavated 
along the softer bands in the crystalline rocks. 
The thousands of lakes, many of them of considerable 
size, scattered over the vast Laurentian regions of North- 
ern Canada, were regarded as due to the deep decay of 
these rocks by long continued atmospheric causes and the 
subsequent sweeping away of the softened rock by glacial 
and other denuding agencies. These lakes all lie in rock 
basins, and, owing to the generally level nature of the 
country, many of them have two outlets. They are often 
shallow and full of islands, running in chains, their arrange- 
