A'iagara Gorge and Postglacial Time. — Uphain. 237 
this eastern tributary undoubtedly had cut a deep ravine, with 
falls and cascades, along its last mile or more. At the east end 
of the Foster flats and farther up stream, the preglacial Fish 
creek had only a very shallow valley, slightly hollowing but not 
trenching the bed rocks. 
Under this view we see readily how the Niagara river with- 
drew its waters from the low cataract at the Foster flats. On 
reaching the head of the preglacial ravine in the gradual re- 
cession of the falls, the main current, which passed on the south- 
east side of the flats, speedily eroded a deeper channel, far be- 
low its former bed above that cataract, because the drift filling 
the old ravine was easily swept away. Along a distance of 
nearly two miles, adjoining the Foster flats and northeasterly, 
the river flowed afterwards in powerful rap'ds, eroding this 
part of the gorge into the rock strata to its present depth ; and 
the greater depth, with slow and smooth current, for a half 
mile between the flats and the Whirlpool may be due to such 
deep erosion by the preglacial stream there, its ravine having 
been cut down nearly to the bottom of the St. David's chan- 
nel before coming to their junction. 
Evidently the preglacial brook that coincided somewhat 
nearly with the present Fish creek could not have passed 
northward through the Niagara escarpment in the course of 
the river gorge. The crest of the escarpment there is higher 
than the land stretching south and southwest to the Whirl- 
pool. The gorge has no widening, such as is a most re- 
markable feature of the old channel at St. David's, where it 
approaches and cuts the escarpment; nor does it show evi- 
dence of much greater age there, as geologists count time, 
than along any other part, even near the present cataract. 
Prof. G. F. Wright has proved, instead, that the oldest part 
of the gorge, at and near the escarpment, can have endured 
the inevitable weathering of its cliffs no longer than 10,000 
years, and that indeed its age, which is also the entire age of 
the Niagara river and falls, niav be a considerably shorter 
period.* 
Above the Whirlpool it seems very clear to my mind that 
the gorge erosion was much aided by the preglacial St. 
David's stream for the distance of one mile occupied by the 
*"\'e\v Methofl ot Kstimating the Age of Niagara Falls." Popular Science 
Monthly, vol. Iv, pp. 145-154, with six figures in the text, June, 1899. 
