110 WwW. UPHAM—NIAGARA GORGE AND SAINT DAVIDS CHANNEL. 
arguments and computations of Spencer,* which give 32,000 years as 
the age of the Niagara river. About three-fourths of that period are de- 
rived from the hypothesis of the eastward outlet from the upper lakes, 
which, as I believe, is untenable, or, at the most, had only a very short 
existence. Leaving out that element of the problem as insignificant and 
dividing the length of the Niagara gorge (about 62 miles) by the recent 
rate of average annual recession of the falls (nearly 5 feet), we have ap- 
proximately 7,000 years, as announced by Gilbert at the Buffalo meeting 
of the American Association for the Advancement of Science in 1886, as 
the probable time required for the erosion of the gorge. 
This measure, which (not to be too exact in figures depending on the 
varying conditions of the Niagara history) we may place in round num- 
bers as between 5,000 and 10,000 years, is of great interest to geologists 
because it is at the same time the duration of the period since the end 
of the Ice age, or, speaking more definitely, since the retreat of the con- 
tinental glacier from the northern United States and Canada. It may be 
so accepted with confidence, for it agrees with the estimates and computa- 
tions independently made for the same period by Professor N. H. Win- 
chell, from the recession of the falls of Saint Anthony; by Dr Andrews, 
and recently-also by Mr. Frank Leverett, from the shore erosion of lake 
Michigan and the accumulation of sand at its south end ; by Professor 
G. Frederick Wright, from the filling of depressions among kames and 
eskers, and from erosion by streams tributary to lake Erie; and by Pro- 
fessor B. K. Emerson, from postglacial deposition in the valley of the 
Connecticut river. In Europe, likewise, numerous estimates of the lapse 
of time since the Glacial period, as collated by Hansen, are found to be 
comprised between the limits of 5,000 and 12,000 years, being thus well 
harmonious with the measure given us by Niagara falls. 
*Am. Jour. Sei., uit, vol. xlviii, Novy., 1894, pp. 455-472. Am. Geologist, vol. xiv, Noy., 1894, pp. 289- 
301. Eleventh Annual Report of the Commissioners of the State Reservation at Niagara, for the 
year 1894, pp. 99-117, with maps, sections, and views from photographs. 
