Our reading of the history should begin at the site of the present cataract, since the records of later events are so much the more complete and legible, and it should ever be our plan to proceed from the clearly written pages to those half effaced and illegible.
As we have learned, the most abrupt change in the cross section of the gorge is found a little above the railroad bridges, where the Upper Great Gorge is joined to the Gorge of the Whirlpool Rapids ([Fig. 389]). In view of the remarkably uniform cross section of the Upper Great Gorge, there is no reason to doubt that it has been drilled throughout under essentially the same volume of water, and that its lower limit marks the position of the former cataract when the waters from the upper lakes were transferred from the “North Bay Outlet” into the present or “Port Huron Outlet” and Lake Erie. As the upper limit of the Gorge of the Whirlpool Rapids thus corresponds to the closing of the “North Bay Outlet” and the extinction of the Nipissing Great Lakes, so its lower limit doubtless corresponds to the opening of that outlet and the termination of the preceding Algonquin stage; for in the stage of the Nipissing lakes the water of the upper lakes, as we have learned, reached the ocean through the northern outlet.
Mr. Frank Taylor, who has given much study to the problem of Niagaran history, believes that the Middle Great Gorge, comprising the Eddy Basin and the Cove section, represents the gorge drilling which occurred during the later stage of Lake Algonquin after the “Trent Outlet” had been closed and the waters of the upper lakes had been turned into the Erie Basin.
Summarizing, then, the episodes of the lake and the gorge history are to be correlated as follows:—
| Glacial Lake | Niagara Gorge |
| Early Lakes Iroquois and Algonquin. | Drilling of the gorge from the Lewiston Escarpment to the Cove section above the Wintergreen Flats. |
| Later Lakes Iroquois and Algonquin with upper lakes discharging into Erie basin. | Drilling of Middle Great Gorge. |
| Nipissing Great Lakes with the upper lake waters diverted from Lake Erie. | Drilling of the narrow Gorge of the Whirlpool Rapids. |
| Recent St. Lawrence drainage since the waters of the upper lakes were discharged into Lake Erie through occupation of the Port Huron Outlet. | Drilling of Upper Great Gorge to the present cataract. |
Time measures of the Niagara clock.—In primitive civilizations time has sometimes been measured by the lapse necessary to accomplish a certain task, such, for example, as walking the distance between two points; and the natural clock of Niagara has been of this type. But men possess differences in strength and speed, and the same man is at some times more vigorous than at others, and so does not work at a uniform rate. The cataract of Niagara, charged with the pent-up energy of the waters of all the Great Lakes, can rush its work as it is clearly unable to do at times when the greater part of this energy has been diverted. Units of distance measured along the gorge are therefore too unreliable for our use, with the unique exception of the stretch from the railroad bridges to the site of the present cataract, within which stretch the gorge cross sections are so nearly uniform as to indicate an approximation to continued application of uniform energy. This energy we may actually measure in the existing cataract, and so fix upon a unit of time that can be translated into years.
In order to secure the normal rate of recession of this Upper Great Gorge, we should add to the volume of water in the Canadian Fall that now passing over the American; and for the reason that the blocks which fall from the cataract cornice and are the tools of the drilling instrument approximate to a definite size fixed by their joint planes, the effect of this added energy it is not easy to estimate. We may be sure, however, that the drilling action would be somewhat increased by the junction of the two Falls, and thus are assured that the average rate of recession within the Upper Great Gorge has been somewhat in excess of the five feet per year determined by Gilbert for the present Canadian Fall. The Upper Great Gorge is about two miles in length, and its beginning may thus be dated near the dawning of the Christian Era. The Whirlpool Gorge was cut when the ice vacated the North Bay Outlet in Canada, and still lay as a broad mantle over all northeastern Canada. For the earlier gorge and lake stages, the time estimates are hardly more than guesses, and we need not now concern ourselves with them.
The horologe of late glacial time in Scandinavia.—A glacial timepiece of somewhat different construction and of greater refinement has been made use of in Scandinavia to derive the “geochronology of the last 12,000 years.” Instead of retreating over the land and impounding the drainage as it did so, the latest continental glacier of Scandinavia ended below sea level, and as it retired, its great subglacial river laid down a giant esker known as the Stockholm Os, which was bordered by a delta and fringed on either side by water-laid moraines of the block type. These recessional moraines are upon the average less than 1000 feet apart, and are believed to have each been formed in a single season. The delta deposits which surround the esker are of thin-banded clay, and as an additional uppermost band is found outside every moraine, these bands are also believed to represent each the delta deposit of a single year. In studies extending over many years, Baron de Geer, with the aid of a large body of student helpers, has succeeded in completing a count of moraines and clay layers, and so in determining the time to be 12,000 years since the ice front of the latest continental glacier lay across southern Sweden. The fertility of conception and the thoroughness of execution of this epoch-making investigation recommend its conclusion to the scientific reader.
Reading References for Chapter XXV
G. K. Gilbert. Niagara Falls and their History, Nat. Geogr. Soc. Mon., vol. 1, No. 7, 1895, pp. 203-236.