Spencer — Another Episode in the History of Niagara. 449 



valley above the cauldron. Indeed the sloping features are 

 preserved in the extension of the whirlpool valley, where not 

 remodified by the modern Niagara, showing that we have not 

 far to go for evidence. 



The diminution of the volume of the river would not 

 explain the shallowness of the channel at the Whirlpool Rapids. 

 We find to-day many small streams near the Niagara district 

 which are excavating their canons directly through the lower 

 hard layers of the same strata as in the gorge, showing that the 

 streams of insignificant volume are penetrating the rocks to 

 the base-level of erosion as well as those of great magnitude. 

 Consequently, Mr. Taylor's hypothesis does not satisfy the 

 shallowness of the Whirlpool Rapids, which demands a reduc- 

 tion in the height of the falls, such as has been found to have 

 obtained. 



The other question which the hypothesis of the glacial dam 

 was hoped to explain was the narrowness of the section of the 

 Whirlpool Rapids. If the waters of the Huron basin had 

 been completely diverted from the Niagara drainage at this 

 time, the narrowing but not shallowing of the canon might be 

 partly explained. But of it there appears no evidence. From 

 the preservation of the river banks outside of the narrows of 

 the gorge, the width of the channel is seen to have been main- 

 tained at the full breadth and depth. This statement may be 

 seen somewhat illustrated in fig. 1 (page 441), below which there 

 is an explanatory note. The constriction applies to the gorge 

 alone. This section differed materially from the country above 

 and below it, as here the Niagara River came to occupy a shal- 

 low and small preglacial valley, which was filled by drift to the 

 depth of forty or fifty feet, as seen in the banks of the deserted 

 channel of the river beyond the edge of the chasm. The depth 

 of the depression was greater in its center, and the river took 

 possession of the deeper portion, and upon the removal of the 

 drift, sunk within the narrow gorge. This is found to have 

 been the case, for at the place where Mr. Taylor describes the 

 pause of the falls, at the foot of the present Whirlpool Rapids, 

 the surface rocky floor of the old valley at that point is 20 

 feet higher than in the deeper remains of the channel exposed 

 above it ; thus showing that there was a deeper medial chan- 

 nel subsequently developed into the narrow chasms. This 

 shallow-buried valley began in Johnson's ridge, just above 

 the railway bridges (see figs. 1 and 2), and extended to the 

 whirlpool, whose cauldron is only the deeper extension of the 

 same ancient channel. Accordingly it is readily seen that the 

 length of the section of the Narrows and that of the preglacial 

 depression coincide. 



When the Falls had retreated as far as the whirlpool, and 

 had removed the rockv barrier at its outlet, the buried channel 



