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a At its extreme southern extremity Lake Huron contracts itself into the St. 
_ Clair River, a stream which flows due south for 44 miles between moderately 
high banks before expanding into the small lake of the same name. Lake St. 
_ lair is 30 miles long by 24 wide, with an area of 360 square miles, and a depth 
mor 12 to 22 feet. It, again, communicates with Lake Erie by the Detroit River, 
_ which varies considerably in width, and is studded with numerous islands. 
Lake Erie differs considerably from the other lakes, and especially from the 
Upper Lakes in its depth; its average depth is only 80 feet; the west end is shal- 
low, the deepest points, which do not exceed 220 feet, occurring off Long Point on 
the north shore. It is 240 miles long, 57 broad at its broadest point, and has an 
area of 9,000 square miles. The fall from Lake Huron through the St. Clair 
and Detroit rivers is very gentle, so that Lake Erie exhibits a difference of level 
of 13 feet from Lake Huron; it is in the Niagara River, which forms the outlet 
of the Lake at the eastern extremity, that the great fall occurs over the Niagara 
escarpment, so that in its stretch of 36 miles from Lake Erie to Lake Ontario a 
difference of levels of 230 feet is achieved, two-thirds of which is accomplished 
at the Falls. Lake Ontario is 185 miles wide,40 broad, and has a maximum 
depth of 600-700 feet. Few rivers of importance fall in on the North Shore ; 
of these the Trent, which, with the aid of its tributary, the Otonabee River, 
drains several small lakes before falling into the Bay of Quinte, may be men- 
tioned. 
At its eastern end the outlet of the lake into the St. Lawrence River, which 
here first attains its name, is studded with the “Thousand Islands,” and before 
_ the river is augmented by the Ottawa at Vaudreuil it expands into several quiet 
_ lake-like reaches and plunges down in long and picturesque intervening rapids. 
To complete the account of the St. Lawrence system, a short reference to the 
affluents of the Ottawa River, situated within the Province of Ontario is neces- 
sary. Lake Temiscaming, the largest and deepest expansion of the Ottawa, re- 
ceives the most northerly of these; it isa magnificent stretch of navigable water, 
67 miles in length, and varying in breadth from 6 to 8 miles. The ascertained 
height is 612 feet. The River Blanche, which drains a clayey region of the 
Height of Land, and the Montreal River which comes from the north-west, and 
in its course receives one of the outlets of Lake Tamagaming, are the chief tri- 
butaries. Immediately to the east of Lake Nipissing is the watershed between 
the Georgian Bay and an important affluent of the Ottawa,the river Matawan. 
Between the mouth of this river and the City of Ottawa, several important streams, 
which drain the lakes of the south-eastern tract of the Archean region, fall 
into the Ottawa on its right bank, viz., the Petewawa, 140 miles long, with a 
drainage area of 2,200 square miles, Black River, 120 miles long, with an area of 
_ °1,120 square miles, and the Madawaska, 240 miles long, and an area of 4,100 
square miles, 
Geologists, it is indicated above, have found evidence of many changes in the 
outlines of the St. Lawrence Basin. At one time the Great Lakes must have 
_ been salt water, their northern shores forming the coast line of the high Archean 
_ land to the north. Maritime plants on the north shore of Lake Superior, and 
‘marine shrimps in its depths which were able to accommodate themselves 
gradually to the change in salinity of the water as the land rose, are still found 
as evidence of this. But, even since their conversion into inland seas, the out- 
lines of the modern lakes by no means agree with what they must have been in 
the past. Lake Erie, for example, is a comparatively modern way for the waters 
of the Upper Lakes to escape to the sea, and it is probabie that Lake Nipissing 
