PHYSICAL FEATURES. 105 
of about one mile by a preglacial stream valley, which extends southeast- 
ward, in the direction of the Whirlpool, about 13 miles. At its head, 
this old valley or channel, as it now has expression in the surface con- 
tour, is filled up evenly to the adjoining country with drift deposits, 
partly consisting of kame and esker gravel and sand and partly of under- 
lying till. 
The continuation of the preglacial channel, however, although at this 
present water divide filled and concealed by the glacial drift, is revealed 
1 to 12 miles farther southeast by the ravine of Bowman creek, and espe- 
cially by the deep basin of the Whirlpool, where only drift forms its 
northwest side, in remarkable contrast with the inclosing rock walls of all 
the Niagara gorge excepting at that place. Professor C. H. Hitchcock 
informs me that nearly all the drift there filling the old channel is boulder 
clay or till, most stony in the lower part of the section, and perhaps divis- 
ible in two or three deposits, laid down during successive stages of the 
Glacial period. 
PROBABLE PREGLACIAL EXTENT ABOVE THE WHIRLPOOL 
In the careful studies of the history of the Niagara river and gorge by 
Pohlman * and Gilbert,f as in the earlier observations of Lyell and Hall, 
the coincidence of the postglacial Niagara gorge with the preglacial Saint 
Davids channel at the Whirlpool is clearly recognized. The present river 
here has washed out the drift that filled the ancient channel and appar- 
ently reached to the bottom of the Whirlpool, about 130 feet above the 
sea. Thence the preglacial Saint Davids stream bed, beneath the drift, 
has probably this depth of 117 feet below the level of lake Ontario, or 
more, along its course past Saint Davids and onward to the deep central 
- part of the Lake Ontario basin. The preglacial stream, as Pohlman has 
shown, drained the shallow Tonawanda valley, but not the area of lake 
Erie, which was tributary by a preglacial outlet, discovered by Spencer, 
along the present Grand River and Dundas valleys, to the west end of 
the area of lake Ontario, while that area was a river basin with free 
drainage. 
At the Whirlpool the Saint Davids 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 ravine 400 feet deep below the Medina falls and a quarter of a 
mile wide, this preglacial stream doubtless also had cut an important 
*Proc, Am. Assoc. Ady. Sci., yol. xxxii, 1883, p. 202; vol. xxxy, 1886, pp. 221, 222. Trans. Am. 
Inst. Mining Engineers, vol. xvii, Oct., 1888, pp. 322-338, with maps and sections. 
7 Sixth Annual Report of the Commissioners of the State Reservation at Niagara, for the year 
1889, pp. 61-84, with 8 plates (maps and sections) ; also in the Smithsonian Report for 1890. Mono. 
graphs of the National Geographic Society, vol. 1, Sept., 1895, pp. 203-236, with 21 figures in the text- 
