How the Lakes were Formed -- Once a Table Land -- Buried River Beds -- Relics of Nature's Ancient Handiwork -- Ancient Rivers -- The Laurentian, Huronian and Erigan Rivers -- Lake Region Submerged -- Tilting up of the Land from the Northeast -- District Re-elevated -- Birth of the Great Lakes -- Processes by which They attained Present Beds -- Future Drainage into the. Mississippi -- Great Scientific Interest.
WHERE the chain of Great Lakes now tosses its restless waters, there once stood a tableland, elevated many hundred feet above the prehistoric ocean, and drained by an ancient water-way, which is yet faintly outlined in the trend of the present lakes. Among the marvels of the present generation are the wonderful advances made in the science of geology. The vast movements of the universe have left their indelible records stamped on the face of nature, but visible only to those who have patiently studied and read these signs.
It has been only during the past fifteen or twenty years that serious work has been attempted on revealing the geological history of the Great Lakes. The making of a continent is a work of ages. Through unnumbered centuries lands have slowly emerged from the vastness of the ocean, mountains have been built and valleys carved by the mighty forces of nature, forever active. Viewed from geological time the work is not completed, and looking alone to our Great Lakes, their present boundaries and trend are only transitory. To the northward the land is slowly rising at the estimated rate of several feet a century and slowly tilting the lakes to the southward, a matter of small importance in a century, but destined in the eons yet to come, to work important changes, should the terrestrial forces, now active, continue uninterruptedly along their present lines of energy.
This is scientific speculation. But to go back from the present into the realms of the past is history, and in that direction the tracings of the ages are as wonderful as they are real. Dr. J. W. Spencer, one of the geologists who have made special study of the creation of the Great Lakes, says that the last touch in the completion of the North American continent has been the making of these lakes. He describes the ancient conditions. In very ancient times," he says, "the lake district formed a great plateau at a considerable altitude above the sea, with some bordering mountains or high lands." It was high enough to permit the excavation of deep valleys, many of which have long since been filled up with sand and drift and now lie beneath the lake waters. The sea was then farther distant from the present lake region than now.
Ancient Rivers. -- The courses of these buried river beds have been traced with considerable detail during recent years. They are described by Mr. Spencer in an article in the Popular Science Monthly, on " How the Great Lakes were Built," from which the following account is by permission abridged: "In the lake district wells have been sunk for considerable depths for water, oil and gas. On the now level plains the borings have often penetrated great depths of loose rock and dirt deposits before reaching the solid strata, yet, perhaps, in proximity, the bedded rocks appear near the surface of the country. These depressions are portions of ancient valleys, which have been filled often to depths of 500 feet, and in some cases probably to 1,000 feet. By chains of borings the buried valleys may be traced; their general course is frequently shown by the surface features; but without the borings their great depth would not be suspected."
From Georgian Bay, continues Doctor Spencer, the ancient channel is buried below drift deposits to a known depth of 700 feet, and almost certainly the drift reaches to a depth of 1,000 feet beneath the highest obstructing ridges. The course of the channel passes through Lake Simcoe and enters the Ontario valley about 20 miles east of Toronto, where i the deep trench is made known by the surroundings in the lakes. Throughout the Ontario valley the Laurentian river flowed at the foot of a high escarpment, now submerged. At the eastern end of Lake Ontario the channel turned toward the present outlet of the lake and then down what is now the modern course of the St. Lawrence to the sea.
One of the great tributaries was the Huronian river, crossing the southern portion of Michigan, as shown upon the map, and extending through Saginaw Bay to join the Laurentian river farther north. The Superior outlet is supposed to have crossed the upper peninsula of Michigan and joined the branch, draining from the northern end of what is now Lake Michigan.
The now shallow Erie basin was then a portion of a plain, across which the ancient Erigan river flowed in a valley 200 feet or more in depth. One of the buried and submerged tributaries at Cleveland was described by Dr. J. S. Newberry, others by Dr. T. Sterry Hunt, and those near Buffalo by Dr. J. Pohlrnan. From the Erie basin the Erigan river crossed by a channel about forty miles west of the Niagara river, which did not then exist, and passed down the Dundas valley into the head of the Ontario basin and farther eastward joined the Laurentian river. There were no great waterfalls, though rapids must have existed.
In the highlands to the south of the lakes, the ancient streams were tributary to the Laurentian, in place of to the modern Ohio and Susquehanna rivers. The Alleghany flowed to the Erie basin, as did also the upper Ohio. These and other streams now reversed were tributaries of the Erigan river. In New York the upper Susquehanna and some tributaries descended through the "finger lakes" to the Laurentian river as it passed through the Ontario basin. The Laurentian valley and its tributaries were completed before the ice age. As for the modification of the ancient topography by glacial action, it could have been only slight, and does not appear to have been more than the sweeping of loose geological dust into the valleys, or on to the highlands to the south. It was this filling of the old channels with drift that closed the ancient drainage of the Laurentian valley, which at a later date gave rise to the lake basins.
Lake Regions Submerged. -- After the obstruction of the valleys with drift, the whole lake region was submerged and coast lines were formed. These old shore lines may now be traced in the western and central portions of the lake regions, for toward the northeast the waters extended indefinitely. The embayment, called Warren Gulf, covered 200,000 square miles of the lake region. The greater portion of the modern elevation of the region has been recorded in the tilting of the beach lines, and this tilting must have occurred after the glacial epoch. At the head of Lake Erie the deformation of the old water planes is not over a very few inches in a mile. while it increases toward the northeast, so that it amounts to four feet per mile northeast of Lake Huron, and seven feet per mile near the outlet of Lake Ontario and north of the Adirondack Mountains, to which locality Mr. Spencer has traced the deserted shores all the way from the head of Lake Michigan.
Lake Erie, as shown on the map, was very small. In the Niagara district was a strait or lakelet, at the first without a fall. The tilting of the land to the northeast continued and the head of Lake Ontario rose 363 feet above the sea level, the foot of Lake Ontario 730 feet and the northeast corner of the Adirondacks 1,500 feet. This warping up of the continent interposed a barrier to the free communication between the waters of the lakes and the sea, and now maintains Lake Ontario 247 feet above the ocean level. The upper lakes were the first to sink far within their basins (see Fig. 3), but later even the Iroquois Gulf was contracted so as not to occupy even the head of the present Ontario basin (see Fig. 3).
The great deformation of the whole region since the close of the Iroquois episode has from that day to this been slowly raising the northeastern rims of the lake basin, so as to cause them to flood more and more the lowlands and valleys at their southwestern extremities, and even to raise the waters so high as to cover some of the deserted shores in those directions. At the same time the waters are leaving their old margins at their northeastern ends, as shown on the map (Fig. 3).
It is estimated that the Iroquois Gulf sank below the Iroquois plane about fourteen thousand years ago; but that the waters of Lake Huron, which had been emptying by way of the Nipissing strait for twenty-four thousand years, were turned into Lake Erie only eight thousand years ago. Again, after the waters of the Ontario basin had sunk much below the present western margin of the lakes, they were rising again to near their present height only some three thousand years ago.
Of the absolute amount of rise of the continent we do not know, for the axis of uplift has not been ascertained, but it is evidently in the interior of the continent. The differential rate of elevation varies, being about a foot and a quarter a century in the Niagara district, two feet northeast of Lake Huron, and nearly four feet north of the Adirondacks.
Future Drainage into the Mississippi. -- With the land rising as at present, it will be only a matter of time until the northeastern rim of Lake Erie will be so high that the drainage must turn into Lake Huron, and thence by way of Lake Michigan and the Chicago canal into the Mississippi, and Niagara Falls will then end their life history. Some fifteen hundred years ago there was a barrier about a mile north of the present site of the Falls that had risen so high in the general regional uplift as to actually cause some of the waters of the upper lakes to overflow where the Chicago canal is now being built; but, owing to the peculiar buried valley just behind this ridge crossing Niagara river, when the falls had passed the barrier, before the change of outlet of the upper lakes from the Niagara to the Mississippi was completed, the upper lakes were rapidly lowered, and this re-established the life of the Niagara for some time longer. It is calculated that in five thousand years the change in outlet from the Niagara to the Mississippi will occur. The commencement of the Warren Gulf epoch is estimated to have been sixty thousand years ago.
This story of the Great Lakes is arousing keen scientific interest. At the annual meeting of the American Association for the Advancement of Science, held at Detroit in August, 1897, papers on this subject were read by Prof. G. K. Gilbert and by Doctor Spencer, and at the meeting of the International Society for the Advancement of Science, held a few weeks later at Toronto, the same subject was exhaustively discussed. In geological time the formation of the Great Lakes is only an episode, but in human history an occurrence of stupendous significance.
In his paper, alluded to above, Professor Gilbert concludes that Lake Ontario is increasing slowly in area by the rising of the outlet. He says: "Lake Ontario lies altogether southwest of the isobar of its outlet, and the water is encroaching on all its shores. The estimated vertical rise at Hamilton is six inches per century. The whole coast of Lake Erie is also being submerged, the estimated rate at Toledo and Sandusky being eight or nine inches per century."
Professor Gilbert also says: "The slow changes of mean water level are concealed from ordinary observation by the more rapid and impressive changes due to variations of volume, but they are worthy of consideration in the planning of engineering works of a permanent character." He does not claim that his estimates of the rate of this movement are beyond question, although the probability of large error is small. He estimates that the rise of the lake level at Chicago is about one inch in ten years. The change of level, he computes, is such that along a line one hundred miles in length at right angle to the axis of tilting it would amount to five inches per century. On this basis he estimates that in five hundred years the lake would (without artificial interference) overflow through its old channel west of the city at high stages of the lake; that at ordinary stages it would overflow in a thousand years; that in two thousand years it would draw away half of the outflow of the lakes, the other half still following its present course; that in three thousand years the entire outflow of the upper lakes would be westward through the Chicago outlet. These computations of course proceed on the assumption that the movement will continue at the present computed rate. Whether it will so continue or not is beyond knowledge. The forces that are concerned in these great movements of the surface of the earth are not fully known at present. How long a given movement will continue can only be conjectured.
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Some of the transcription work was also done by Brendon Baillod, who maintains an excellent guide to Great Lakes Shipwreck Research.