Since the retreat of the last ice-sheet and since the waters of glacial lake Warren were drained off through the Mohawk valley, the Niagara river has cut out a great canyon from Lewiston to the Horseshoe fall, 6½ miles long, mostly over 300 feet deep, and more than 1,000 feet wide. When studied in detail it soon becomes apparent that nearly all of the gorge has been made by a great cataract, in volume substantially like the present falls; but there are two or three parts that obviously demand some other explanation. One of these is the comparatively narrow and shallow gorge of the Whirlpool rapids, the origin of which it is the particular object of this paper to discuss.
There are two distinct classes of facts which contribute to the unraveling of the gorge history. One is derived from the study of the characters of the gorge itself, . . .