GLACIAL PHENOMENA OF NORTH AMERICA. 71 



where not only the growth of vegetable matter but the 



wash from the sides and the dust blown by winds would 

 unite their forces to augment the rate. If the origin is 

 placed 10,000 years back that would imply a rate of ac- 

 cumulation sufficiently slow, namely, an inch in one 

 hundred years. 



United with this calculation is that of Prof. X. II. YVin- 

 chell, concerning the recession of the falls of St. Anthony. 

 This cataract has receded about eight miles since the 

 close of the glacial epoch. The old channel from Minne- 

 apolis to the Minnesota river is west of the present gorge 

 and is filled with glacial debris. Since the falls were dis- 

 covered by Hennepin in 1680 the recession has been 

 about 1,000 feet, an average of about five feet per year. 

 This would give only about 9,000 years for the erosion 

 since the glacial epoch. 1 



To geologists, probably the gorge below Niagara Falls 

 has been the most convincing evidence of the great antiq- 

 uity of the glacial age. A preglacial channel exists be- 

 low the Whirlpool, reaching Lake Ontario at St. Davids, 

 some distance west of the present mouth of the river. 

 This old channel was tilled with glacial debris, so as to 

 turn the water into its present course. In 1<S41 Professor 

 Hall and Sir Charles Lyell, assuming that the whole 

 gorge, from Lewiston to the present falls, had been 

 formed since the filling up of the channel below the 

 Whirlpool, estimated that the smallest amount of time 

 which would suffice for this task was 30,000 years, and 

 that probably a much longer period was consumed ; but 

 these eminent observers overlooked one circumstance of 

 the very greatest significance, to which the late Mr. 

 Thomas G. Belt has called attention. This paper (which 



*See Fifth Annual Report of the Minnesota Geological Survey, pp. 15G-189. 



