26o The American Geologist. October, i898 
retreat of the Ontario waters toward the north; and that, during the 
later part of this recession of the falls, past the Whirlpool rapids, the 
return to the present amount of 326 feet descent was interrupted by 
the rising of the level of the lake in the gorge to a hight of 75 feet 
above its present level, thus reducing the actual fall of the river to 
250 feet. The evidence of this is preserved in the remains of a ter- 
race deposit opposite the foot of Foster's flats and a corresponding 
terrace just outside the mouth of the gorge; and these terraces, with 
other parts of the shoreline in the Ontario basin which marks the rise 
of the water so as to flood the Niagara gorge, are here named the 
Niagara strand. The rising of the waters was occasioned by the lift- 
ing of the barrier at the outlet of lake Ontaridl to an elevation 100 
feet higher than now. By the subsequent erosion of this barrier, 
which was partly composed of drift, the actual fall of the Niagara 
waters has been increased to its present figure. The reduction of the 
descent of the river is found to be sufficient to account for the shal- 
lowness of the channel at the Whirlpool rapids. The narrowness 
of this section is explained by the fact that the youthful Niagara took 
possession of a small preglacial valley there, giving greater depth 
to the river. It is further probable that the volume of the river was 
less at that time, since it is supposed that a portion of the outflow of 
the great lakes passed to the Mississippi. 
15. The Age of Niagara Falls as Indicated by the Erosion at 
the Mouth of the Gorge. By Prof. G. Frederick Wright, 
Oberlin, Ohio. The late Dr. James Hall early noted the significant 
fact that "the outlet of the chasm below Niagara falls is scarcely wider 
than elsewhere along its course." Clearly this is important evidence 
of the late date of its origin, and it has been used by the author and 
others in support of the short estimates which have been made con- 
cerning the length of time separating us from the Glacial period. A 
close examination made by the author this summer greatly strength- 
ens the force of the argument, since he found that the disintegrating 
forces tending to enlarge the outlet and to give it a V-shape are more 
rapid than has been supposed. The depth of the gorge at the outlet, 
from the top of the Niagara limestone to the river, is 340 feet. The 
thickness of that formation of limestone at the surface is here, how- 
ever, only about 40 feet; while the soft Niagara shales underlying 
it are from 60 to 75 feet thick. Below there is a Jti-atum of Clin- 
ton limestone 30 feet in thickness, and below that a shaly deposit of 
70 feet. The Niagara shales at this point have never been covered 
by talus: so that they have always been accessible to disintegration 
by atmospheric agencies. 
Somewhat over forty years ago, a railroad was built along the 
face of the eastern side of the gorge, affording an opportunity to ob- 
serve the rate of disintegration. All along where a perpendicular ex- 
posure was made, the shale has crumbled away to an extent of sev- 
eral feet, and in some places to that of twenty feet. A conservative 
