Niagara Gorge and Postglacial Time. — Upham. 235 
PREGLACIAL EROSION IN THE COURSE OF THE 
NIAGARA GORGE, AND ITS RELATION TO 
ESTIMATES OF POSTGLACIAL TIME. 
By Warren Upham, St Paul, Minn. 
In the careful studies of the history of the Niagara river 
and gorge by Pohlman* and Gilbert,! as in the earlier ob- 
servations of Lyell and Hall, the coincidence of the post- 
glacial Niagara gorge with the preglacial St. David's chan- 
nel at the Whirlpool is clearly recognized. The present river 
there has washed out the drift that filled the ancient chan- 
nel and apparently reached to the bottom of the Whirlpool, 
about 130 feet above the sea. Thence the preglacial St. Dav- 
id's stream bed, beneath the drift, has probably this depth of 
117 feet below the level of lake Ontario, or more, along its 
course past St. David's and onward to the deep central part 
of the lake Ontario basin. 
The preglacial stream, as Pohlman has shown, drained the 
shallow Tonawanda vallev, but not the area of lake Erie. At 
the Whirlpool this St. David's stream, according to Pohlman, 
plunged down in a cataract from the hard Medina sandstone 
bed, which is underlain and overlain by soft shales. Having 
at this place eroded a valley or ralvine 400 feet deep and a 
quarter of a mile wide, the stream doubtless also had cut an im- 
portant ravine, though of smaller size, along its higher course 
for a considerable distance before reaching the site of the 
Whirlpool. Dr. Pohlman supposes, with sufficient reasons, 
that the St. David's ravine reached along the part of the Niag- 
ara gorge occupied by the Whirlpool rapids, having a middle 
vertical fall over the Clinton limestone and terminating at an 
upper vertical fall over the Niagara limestone, beyond which, 
in its approach from the south, the stream was onl_\- a little 
lower than the adjoining country. 
Some of the latest contributions to the geologic literature 
of Niagara, by Taylor, Hitchcock, and Gilbert, assign to the 
St. David's channel an interglacial age, and regard it as the 
*Proc. Am. Ass. Adv. Sci., vol. xxxii, 1883, p. 202; vol. xxxv, 188G, pp. 
221. 222. Trans. Am. Inst. Alining- Engineers, vol. xvii, pp. 322-338, with 
map* and sections, Oct., 1888. 
ISixth Annual Report of the Commissioners of the State Reservation of 
Niagara, for the year 1 8S9. pp 61-84, with 8 plates (maps and sections); also 
in the Smithsonian Report for 1S9(). Monographs of the National Geographic 
Societv, vol. i, pp. 203-23G, with L'l figures in the text, Sept., 1895. 
