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 Drilling of Middle Great Gorge. with upper lakes discharging into Erie basin. Nipissing Great Lakes with the Drilling of the narrow Gorge of upper lake waters diverted from the Whirlpool Rapids. Lake Erie. Recent St. Lawrence drainage Drilling of Upper Great Gorge to since the waters of the upper lakes the present cataract. were discharged into Lake Erie through occupation of the Port Huron Outlet.