400 



SCIENCE. 



[Vol. V., No. 119. 



instead a wide valley through which a great 

 stream, corresponding to the present Niagara, 

 found its wa} 7 to the head of Lake Ontario, 

 through a deep and continuous gorge. Pro- 

 fessor Spencer, indeed, thinks he can trace the 

 course of this preglacial gorge from near the 

 mouth of Grand River in Canada, northward to 

 Lake Ontario. 1 



We might also infer the relatively late origin 

 of the present channel of the Niagara from the 

 small amount of work which the river has done 

 in its present channel. The Allegheny and 

 Ohio rivers, which lie outside the limit of 

 glaciation, illustrate 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 from three hundred 

 to five hundred feet in depth ; whereas the 

 gorge in the Niagara River below the falls is 

 only about seven miles in length. 



|j|M.W^ Vk,W ' 



sjiMiiiAM'taiMn 



FALLS OF NIAGARA 



That the Niagara gorge is post-glacial, was 

 also shown as early as 1841, by Professor 

 James Hall of the New- York surve} T , who 

 pointed out to Sir Charles Lyell 2 the probable 

 course 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 at the accompanying cut 

 will explain the situation. From the falls to 

 Queenston, the perpendicular bank of the gorge, 

 from two hundred and fifty to three hundred 



1 See Second geological report of Pennsylvania, Q 4 , pp. 

 359 sq. 



2 Lyoll's Travels in America (first series), vol. i. p. 27. 



feet in height, is continuous upon the east side ; 

 but upon the west side, about halfway down, 

 occurs a remarkable indentation known as the 

 ' whirlpool.' Following this bank around, 

 the small streams a, 6, and c expose the rock 

 before descending to the whirlpool, and the 

 rock}- 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 to e is 

 about five hundred feet. Following up the 

 channel of cZ, one comes, at the distance of a 

 half-mile, to the general level of the banks of 

 the river above the cataract, and of the escarp- 

 ment of Niagara limestone, from which the 

 river emerges at Queenston. The opening of 

 the supposed 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. David's 

 is also filled with gravel rather 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 about three miles — is 

 somewhat hypothetical, since for a space of two 

 miles the original features of the countiy are 

 wholly disguised by the glacial deposit, and no 

 wells have been sunk to a sufficient depth to 

 test the question properly. The 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 period 

 there was a narrow gorge, about two hundred 

 and fifty feet deep, extending from the whirl- 

 pool, and perhaps a little above it, to the 

 Ontario level at St. David's. But it is equally 

 clear that the river which wore this gorge was 

 not the Niagara, since a stream of that size 

 must, during the long preglacial period (meas- 

 ured by the eroded channel of the Ohio and 

 Allegheny) , have worn a gorge far longer than 

 that between the whirlpool and the present 

 falls. The preglacial channel from the whirl- 

 pool to St. David's was probably, therefore, as 

 Dr. Pohlman suggests, the work of a com- 

 paratively small stream, with a drainage basin 

 occupjing not more than two or three counties 

 in western New York. 



Considering, now, the gorge from Queenston 

 to the falls of Niagara as the work done by the 

 stream since the close of the glacial period, and 



