Page:Science vol. 5.djvu/432

 SCIENCE.

��[Vol. v., Ko. .

��instead a wide valley Ihrough which a great strenm, correspond log to the present Niagara, found its ivay to the bead of Lake Ontario, through a deep sud continuous gorge. Fro- ftssor Spencer, indeed, thinks be can trace Uie course of this preglacial goi^e from near the mouth of Grand River in Canada, northward to Lake Ontario.'

IVe might also infer the relatively late origin ofthe present channel of the Niagara from the small amount of work which the rivef has done in iis present channel. The Allegheny and Ohiii rivers, which lie ontsidc the limit of glaclation, illiistrnte in a striking degree the extent of preglacial erosion. For a distance of more than a thousand miles, these streams occupy a continuous eroded trough, averaging about a mile in width and n'ora three hundred to five hundred feet in depth; whereas the gorge in the Niagara River helow the falls is only about seven miles in k-ngtli.

���t ihe Niagara

��* pos I -glacial, was early as IS-Jl. Uy Professor Jnnirs Hall of the New-York survey, who pointed out to Sir Charles Lyell' the probable conrse of a preglacial channel, now filled with glacial debris extending from the whirlpool to St. David's, where the level of Lake Ontario is reached. A glance nt the accompanying cut will explain the situation. From the falls to Qncenston. the [wrpendicular bank of the gorge, from two hnndied and fifty to three hundred

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���feet in height, is continuous upon the east side; but upon the west side, about halfway down, occurs a remarkable indentation known^ the 'whirlpool.' Following this baiik around, the small streams u, b, and c expose the rock before descending to the whirlpool, and the rocky bank re-appears at e. But between c and e no rock appears, although the stream d has worn a channel from fifty to a hundred feet deep. The sides and the bed of d consist of the familiar glacial deposit called 'till,' or 'bowlder clay.' The distance from c lo e is about live hundred feet. Following up the channel of d, one comes, at the distance of a half-mile, to the general level of the banks of tbe river above the cataract, and of the escarp- ment of Niagara limestone, from which the river emei-ges at Queenston. The opening of the supiiosed pre-glacial channel to the north- west is, as is shown in the plate, much wider than its entrance at the whirlpool, and the de- scent of three hundred feet to St. David's is rapid. The broad opening toward St. Dai-id'a is also filled with gravel ratber than with till; and this gravel extends southward over the higher level towards the falls, somewhat like the familiar ' lake-ridges ' of Ohio.

It will be seen that the existence of a pre- glacial channel from the whirlpool to St. Da- vid's — a distance of ai>out three miles — is somewhat hypothetical, since for a space of two miles the original fenlnres of the country are wholly disguised by the glacial deijosit, and no wells have been sunk to a sufficient depth to test the question properly. Tbe well to which Sir Charles Lyell referred was probably about the head of the stream c, which is really In the gravel outside the escarpment. Still there is little doubt that before the glacial jieriod thei-e was a narrow gorge, about two hundred and fiflj' feet deep, extending from the whirl- pool, and jjerhaps a little above it, to the Ontario level at SI. David's. Hut it is equally clear that the river which woi-e this gorge was not the Niagara, since a stream of that size must, during the long preglacial period (meas- ured by ibe eroded channel of the Ohio and Allegheny), have worn a goi^e far longer than that between the whirlpool and the present falls. The pivglncial channel from the whirl- pool to St. David's was probably, therefore, as Dr. Fohlman suggests, the work of a com- paratively small stream, with a drainage basin occupying not more than two or three counties in western New York.

Considering, now, llie gorge from Queenston to the falls of Niagara as the work done by the stream since the close of the glacial period, and

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