to four hundred and fifty feet high, and the whole somewhat further submerged. Again it passes through the narrows across the broken mountain ridge into Georgian Bay, where the deep channel skirts the foot of another high escarpment. The old water way across these lakes is shown on map (Fig. 5).
From Georgian Bay the ancient channel is buried below drift deposits to a known depth of seven hundred feet, and almost certainly the drift reaches to a depth of one thousand feet beneath the highest obstructing ridges. The course of the channel passes through Lake Simcoe and enters the Ontario Valley about twenty miles east of Toronto, where the deep trench is made known by the soundings in the lake. The buried valley was broad and comparable to the portions through the lakes. On its western side, but some miles away, it is paralleled by the “mountain” or Niagara escarpment, which reaches to more than fifteen hundred feet above the sea. On the eastern side of the valley the plains are underlaid by solid rock, although these are often covered by drift ridges. Between these rocky boundaries the drift has been penetrated to great depths in many places, yet in the center of the channel the bottom of the filling has never been reached.
Throughout the Ontario Valley the Laurentian Kiver flowed at the foot of a high escarpment now submerged (see Figs. 3, 5, 11). 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. The origin of the barrier across the present outlet of Lake Ontario will be noticed later.
One of the great tributaries was the Huronian River, crossing the southern portion of Michigan, as shown upon the map (Fig. 5), 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 two hundred 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. Pohlman. 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 (Fig. 1) into the head of the Ontario basin, and farther eastward joined the Laurentian River (Fig. 5). All the features of the ancient and drowned valleys are those characterizing ancient topography; that is to say, without the boldnesses and abruptnesses of youthful features and without great waterfalls, although rapids must have existed.