Supposing the cataract to be receding at the rate of fifty yards in forty years, as it is stated by Captain Hall, the ravine which extends from thence to Queenstown, a distance of seven miles, will have required nearly ten thousand years for its excavation; and, at the same rate, it will require upward of thirty-five thousand years for the falls to recede to Lake Erie, a distance of twenty-five miles. The draining of the lake, which is not more than ten or twelve fathoms in average depth, must then take place, causing a tremendous deluge by the sudden escape of its waters. In addition to the gradual erosion of the limestone, which forms the bed of the Niagara at and above the falls, huge masses of the rock are occasionally detached by the undermining of the soft shale upon which it rests. This effect is produced by the action of the spray powerfully thrown back upon the stratum of shale; and hence has arisen the great hollow between the descending flood and the precipice. An immense fragment fell on the 28th of December, 1828, with a crash that shook the glass vessels in the adjoining inn, and was felt at the distance of two miles from the spot. By this disintegration, the angular or horse-shoe form of the great fall was lessened, and its grandeur heightened by the line of the torrent becoming more horizontal. A similar dislocation had occurred in the year 1818; and the aspect of the precipice always so threatening, owing to the wearing away of the lower stratum, as to render it an affair of some real hazard to venture between the falling waters and the rock. Miss Martineau undertook the enterprise, clad in the oil-skin costume used for the expedition, and thus remarks concerning it:--“A hurricane blows up from the cauldron; a deluge drives at you from all parts; and the noise of both wind and waters, reverberated from the cavern, is inconceivable. Our path was sometimes a wet ledge of rock, just broad enough to allow one person at a time to creep along: in other places we walked over heaps of fragments, both slippery and unstable. If all had been dry and quiet, I might probably have thought this path above the boiling basin dangerous, and have trembled to pass it; but, amidst the hubbub of gusts and floods, it appeared so firm a footing, that I had no fear of slipping into the cauldron. From the moment that I perceived we were actually behind the cataract, and not in a mere cloud of spray, the enjoyment was intense. I not only saw the watery curtain before me like tempest-driven snow, but, by momentary glances, could see the crystal roof of this most wonderful of Nature’s palaces. The precise point where the flood quitted the rock was marked by a gush of silvery light, which of course was brighter where the waters were shooting forward, than below, where they fell perpendicularly.” There have been several hair-breadth escapes, and not a few fatal accidents, at Niagara, the relation of which is highly illustrative of Indian magnanimity.