258 



ON THE HYDROLOGY OF THE BASIN 



mention the series lying upon the course of the Otonabee and the Trent, on the north side 

 of Lake Ontario. But the most extensive development of these small surfaces of water 

 occurs in that fiat region of country forming the great southern peninsula of Michigan, 

 which is generally described as covered with a great thickness of drift. 



In the course of the Michigan survey, the topographers have already laid down on the 

 maps fourteen hundred and twenty-five lakes, occupying areas of from one thousand to 

 three thousand five hundred acres, which would be in the proportion of one aci"e of water 

 to thirty-nine acres of land. 



We cannot properly pass from this subject without referring to Lake St. Clair, which is 

 only a shallow depression in the drift. It consists of an expansion of the straits leading 

 down from Lake Huron to Erie, and may be assumed as twenty-one miles in length, by 

 eighteen and a half in width. Its depth, as will be seen by the section, is only twenty 

 feet, and like Lake Erie, which does not exceed eighty-four feet, is the recipient of the 

 alluvial deposits of the rivers which flow into it. The inlet to Lake St. Clair is an inter- 

 esting delta, and islands of alluvium arc constantly forming, which tend to choke up its 

 numerous channels. Although the average depth of Lake St. Clair is about twenty feet, 

 the navigation through it has to pass a channel wliich is naturally about ten feet ; and the 

 dredging out of this channel to the depth of thirteen feet, by the United States Govern- 

 ment, is referred to in another part of this paper. 



A moderate gale of wind soon raises a sea in this shallow lake, causes the whole to be- 

 come turbid, and tends thus to distribute the detrital matter, and to convey it through the 

 Detroit straits into Lake Erie, where similar accumulations, on a larger scale, occur. The 

 depth of Erie over its upper end scarcely averages eighty feet, its deepest part being near 

 the east end, where it begins to narrow towards the outlet, in the direction of Niagara. 

 Here, too, an ordinary storm raises a very heavy and somewhat dangerous sea, and soon 

 disturbs the bottom, and favors the distribution of natural deposits which settle in calmer 

 weather in the upper portion of this shallow basin. 



Reflecting upon the relative levels of these upper lakes, as given in the table before re- 

 ferred to, and the peculiar character of the water-shed which limits the basin on the west 

 side of Lake Michigan, it will be seen that if the barrier now regulating the discharge 

 through the Niagara River were lifted to the extent of about thirty feet, the whole of the 

 great lakes would be converted into one vast sea, on a uniform level, which, while placing 

 under water from eight to nine thousand square miles in Western Canada and Michigan, 

 and the other borders of the lakes, would determine the direction of the outlet of this 

 great basin towards the Mississippi, and place the present dividing ridge from seven to 

 eight feet below the surface of this expanded sheet of water. 



