ton, where it is just large enough to contain the rapid current of water, accords well with the same hypothesis, and there is no ground for suspecting that the excavation was assisted by an original rent in the rocks, because there is no fissure at present in the limestone at the Falls, where the moving waters alone have power to cut their way backwards.

I have already remarked that there will always be insuperable difficulties in the way of estimating with precision the rate of the retrogression of the Falls in former ages, because at every step new strata have been successively exposed at the base of the precipice. According to their softer or harder nature, the undermining process must have been accelerated or retarded. This will be un lerstood by reference to the annexed section (fig. 4.), where the line b, c, d, represents the present surface of the river along which the Falls have recedel. The strata (1, 3, and 7,) are of soft materials; the others, (2, 4, and 8), which slightly project at their termination in the escarpment, are of a more compact and refractory kinl. It has been necessary to exaggerate the southward dip of the strata in this diagram, which is in reality so slight as to be insensible to the eye, being only, as before mentioned, about twenty-five feet in a mile, the river channel sloping in an opposite direction at the rate of fifteen feet in a mile. These two inclinations, taken together, have caused, as Mr. Hall has pointed out in his Survey, a diminution of forty feet in the perpendicular height of the Falls for every mile that they receded southward. By reference to the section, the reader will perceive that when they were situated at the Whirlpool (c), the quartzose sandstone (2), which is extremely hard, was at the base of

Section of the strata along the Niagara River, from Lake Ontario to Lake Erie.-(Chiefly from Hall's Report on the Geology of New York.)

the precipice, and here the Great Cataract may have remained nearly stationary for ages.

In regard to the future retrocession of the Falls, it will be perceived by the same section (fig. 4.), that when they have travelled back two miles, or to i, k, the massive limestone (8), now at the top of the Falls, will then be at their base; and its great hardness may, perhaps, effectually stop the excavating process, if it should not have been previously arrested by the descent of large masses of the same rock from the cliff above. It will also appear that the Falls will continually diminish in height, and should they ever reach Lake Erie, they will intersect entirely different strata from those over which they are now thrown.

The next inquiry into which we are naturally led by our retrospect into the past history of this region, relates to the origin of the Falls. If they were once seven miles northward of their present site, in what manner, and at what geological period, did they first come into existence? In tracing back the series of past events, we have already seen that the last change was the erosion of the great ravine; previously to which occurred the deposition of the freshwater deposit, including fossil shells of recent species, and the bones of the Mastodon. Thirdly, of still older date was the drift or boulder formation which overspreads the whole platform and the face of the escarpment near Queenston, as well as the low country between it and Lake Ontario. Fourthly, the denudation of the line of cliff or escarpment, in which the table-land ends abruptly, preceded the origin of the drift. I shall endeavour to show, in a subsequent chapter, when speaking of Canada, that this drift was of marine origin, and formed when the

whole country was submerged beneath the sea. In the region of the Niagara it is stratified, and though no fossils have as yet been detected in it, similar deposits occur in the valley of the St. Lawrence at Montreal, at a height nearly equal to Lake Erie, where fossil shells, of species such as now inhabit the northern seas, lie buried in the drift.

It is almost superfluous to affirm that a consideration of the geology of the whole basin of the St. Lawrence and the great lakes can alone entitle us to speculate on the state of things which immediately preceded or accompanied the origin of the Great Cataract. To give even a brief sketch of the various phenomena to which our attention must be directed, in order to solve this curious problem, would require a digression of several chapters. At present the shortest and most intelligible way of explaining the results of my observations and reflections on this subject will be to describe the successive changes in the order in which I imagine them to have happened. The first event then to which we must recur is the superficial waste or denudation of the older stratified rocks (from 1 to 10 inclusive, section, fig. 4., p. 37.), all of which had remained nearly undisturbed and horizontal from the era of their formation beneath the sea to a comparatively modern period. That they were all of marine origin is proved by their imbedded corals and shells. They at length emerged slowly, and portions of their edges were removed by the action of the waves and currents, by which cliffs were formed at successive heights, especially where hard limestones (such as Nos. 10 and 8, fig. 4.) at Blackrock and Lewiston, were incumbent on soft shales. After this denudation the whole region was again gradually

submerged, and this event took place during the glacial period, at which time the surfaces of the rocks already denuded were smoothed, polished, and furrowed by glacial action, which operated successively at different levels. The country was then buried under a load of stratified and unstratified sand, gravel, and erratic blocks, occasionally 80, and in some hollows more than 300, feet deep. An old ravine terminating at St. David's, which intersects the limestone platform of the Niagara, and opens into the great escarpment, illustrates the posteriority of this drift to the epoch when the older rocks were denuded. The period of submergence last alluded to was very modern, for the shells then inhabiting the ocean belonged, almost without exception, to species still living in high northern, and some of them in temperate, latitudes. The next great change was the re-emergence of this country, consisting of the ancient denuded rocks, covered indiscriminately with modern marine drift. The upward movement by which this was accomplished was not sudden and instantaneous, but gradual and intermittent. The pauses by which it was interrupted are marked by ancient beach-lines, ridges, and terraces, found at different heights above the present lakes. These ridges and terraces are partly due to the denudation and re-arrangement of the materials of the drift itself, which had previously been deposited on the platform, the sloping face of the escarpments, and in the basins of the great lakes.

As soon as the table-land between Lakes Erie and Ontario emerged and was laid dry, the river Niagara came into existence, the basin of Lake Ontario still continuing to form part of the sea. From that moment