In the most ancient system of which we can obtain an approximately definite knowledge, Lake Huron was not more than half its present size, while Georgian Bay formed the main body, connecting with Huron by a narrow strait. Michigan and Superior occupied about their present limits, but were connected with Huron by rivers rather than short straits; Erie occupied only a fraction of its present position, having no connection with Huron. The waters of the upper lakes were doubtless discharged from the eastern end of Georgian Bay, which then included Lake Nipissing, by way of the Ottawa River, into the St. Lawrence. Thus the Niagara was deprived of about seven-eighths of its present drainage area, and consequently was totally unlike its present self. There is some indication that there may have been an outlet from Georgian Bay by a more southerly route, namely, the Trent River. If this were so, the northern route must have been blocked by the ice, since the Trent Pass is much higher than the one leading from Lake Nipissing, by way of the Ottawa. These are some of the possibilities which must be taken into consideration before any sure calculation can be made as to the age of the Falls, for there must have been an epoch in the history of the river, were it short or long, during which it carried only a very small fraction of the waters which it bears at present. Let us turn again to the gorge of the river itself. We have noted the similarity of structure of its two sides. This similarity is continuous throughout except at about half-way from Queenston to the Falls, where the river makes a turn in its course of almost ninety degrees. On the outside of this angle is the only place in the whole course where the material of the cliff changes. Here there is a break in the solid rock of the bank, which is filled with loose rock and gravel. This rift, to whatever it may be due, is of pre-glacial origin, for it is filled with the same material, the glacial drift, which covers the whole region. The cliff along Lake Ontario also presents very few breaks; but a few miles to the west of Queenston at St. Davids a broad gap is found in the otherwise unbroken wall. This gap is also filled with glacial drift. On its first discovery it was supposed to be a buried valley, and no connection with the Whirlpool was attributed to it. Later it was supposed that the break in the side of the Gorge, and the one at St. Davids, were parts of one and the same course of some pre-glacial stream. This supposition has been proven by the course having been traced through most of its distance by the wells sunk in the region. Later this interpretation of the facts found was destined to furnish further explanations. The question at once arose: How far and where did the upper course of this ancient valley extend? If it had cut across the course of the modern river, there would have been a break in the continuity of the cliff somewhere on the opposite side of the Gorge; but