IN

CHAPTER XXII.

FORMER HIGHER LEVEL OF THE GREAT LAKES.

N the spring of 1865, at the time of the memorable floods, I had occasion to pass over the Great Western Railway from Suspension Bridge to Detroit. From Chatham to the vicinity of Detroit this road runs within sight of Lake St. Clair. On this occasion the country was submerged almost as far as the eye could reach in every direction. Our engineer seemed to be practicing a new species of navigation-rather grallatorial than natatorial. The little lake had become rampant. Outraged by the long encroachments of the land, it had decided to assert again its ancient supremacy. Then I was reminded, if I had never been before, how slight a rise in the lake would submerge entire counties lying upon its borders.

A large part of this Canadian peninsula is scarcely above the ordinary level of the lakes. The whole region looks like an ancient swale and a more ancient lake bottom. The same is true of a considerable breadth on both sides of Lake St. Clair and the Detroit and St. Clair Rivers. Lake St. Clair itself—except when rampant—is little better than a marsh with a river running through it. Among navigators it is the opprobrium of the lakes. One never ceases to hear sailors talk about "the flats," and Congress never ceases to be importuned to make another lake where Nature is in the very act of blotting one out. If the reader has ever taken a steam-boat trip through the lake, he could not avoid discovering that it is the very similitude of ostentatious learning-"all breadth and no depth." The

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bullrushes are boldly invading and occupying it on every hand. A thousand incipient islands are breaking up its continuity. Once it was fifty miles in width and a hundred miles long. A rise of ten or twenty feet would make it that again.

But the whole series of lakes is nearly of the same level from Chicago to Buffalo. The former high waters of Lake St. Clair imply similar floods in the other lakes. Indeed, we easily discover corroboration of this in the topography of the country at Chicago, Detroit, and Toledo. These cities are built upon the slime of the lakes, and a slight elevation of the waters would bury them beneath a new deposit of lacustrine mud. The artesian wells of Toledo are supplied from some of the sandy beds of the ancient lake sediment, which follow the general configuration of the underlying drift, and come to the surface at some higher level back of the city.

These evidences of higher waters lead us to inquire for the cause. They could scarcely be occasioned by a greater volume of water, since the outlets are of sufficient capacity to prevent its accumulation. Nothing but an obstruction of the outlet can explain the phenomenon. This obstruction must have existed at a point where the contiguous shores were sufficiently elevated to prevent a flank movement of the water. It must also have existed at a point beyond or to the eastward of all these obvious traces of the inundation. It could not have been at Mackinac, for that would not have flooded Canada West. It could not have been at the foot of Lake Huron for the same reason, and because the contiguous country is too low. It could not have been at Buffalo for the last-named reason, and also because the country between Buffalo and Lake Ontario belongs to the submerged area. It must have been at the mouth of the Niagara River.

I have said the Niagara River commenced its present gorge during the Champlain Epoch. In reality there was no Niagara River when this work commenced. Lake Erie stretched down the valley of the existing river, and the overflow of its basin wore the notch in the rocky rim which was the beginning of the Niagara River.

Lake Erie stands at present three hundred and thirtyfour feet above Lake Ontario. At the time of which I am speaking it stood three hundred and seventy-two feet above Lake Ontario, and filled the valley of Niagara River as far as the heights above Lewiston (Fig. 84).* Indeed, there are clear evidences, in the form of beaches containing freshwater shells, that the level of the river was once forty feet above the present summit of the falls. No barrier has ever existed to dam the water to this height except the escarpment at Lewiston. This is one hundred and five feet above the summit of the falls, and thirty-eight feet above Lake · Erie. The indications seem to be conclusive that the waters of Lake Erie stood thirty-eight feet higher than at present, and poured over the bluff at Lewiston, in a series of cascades, three hundred and seventy-two feet, to the sea, which at this time filled the basin of Lake Ontario. During the subsequent ages, the mighty stream has dug a gorge in the solid rock, which is seven miles long, two hundred and fifty feet deep, and, on an average, about one thousand feet wide. The material transported from this gorge into Lake Ontario is over three hundred and forty millions

*Explanation of Fig. 84.-The diagram on the following page is intended to illustrate the geological position of Niagara River and Falls, and the ancient lake levels from Lake Ontario to Chicago. The vertical scale is 560 feet to the inch; the horizontal scale is irregular. The diagram is merely a series of sections around the lakes, placed end to end. The dips of the strata are much exaggerated. The two portions of the diagram join each other along the line a, b, c, d, etc. The figures against the vertical dotted lines show the heights in feet above the sea of the points to which the lines extend.

of cubic yards, and weighed nearly seven billions of tons. The time consumed in the execution of this stupendous piece of engineering may be roughly calculated from the observed rate of recession of the falls. In 1842 Professor Hall executed a careful trigonometrical survey of the shorelines and landmarks of the falls. In 1855, twenty-three years later, M. Marcou made careful re-examinations, which he reported to the Geological Society of France. From these data it appears that the Canadian Fall, over which the largest body of water is discharged, has receded, by the wearing of the rocks, to the extent of twelve feet, or a little more than six inches a year. With this clew, we determine that the time required for the excavation of the entire distance from Lewiston is over seventy thousand years. This presumes the rate of recession has always been the same. The more I consider this subject the more I am impressed with a conviction that the rate of recession was formerly more rapid than during the last one hundred years. I am willing to reduce the time consumed to twenty thousand, or even to ten thousand years. Geologists most greedy of time ought to be satisfied with this when it is considered that this interval is but the unit in the arithmetic which calculates the time consumed in the revolutions of the globe. Before the beginning of the excavation of the great gorge, geological agencies had strewed the surface with drift-deposits, some of which had been transported hundreds of miles. Before the transportation of the drift, the basin of Lake Ontario had been scooped out, and the vast erosion of the escarpment at Lewiston had been effected. Before the period of the erosion was that of the solidification of the sediments; and still farther back, the incalculable intervals during which the sediments were accumulating five miles of thickness. At the commencement of the excavation of the gorge, the fauna which populated