548 THE ICE AGE IN NORTH AMERICA. 



size of those south of Lake Michigan, those on Lake Agassiz 

 would have been formed in about 1,000 years. Hence this 

 differential northerly elevation of land over the basin of 

 Lake Agassiz to the extent of 400 feet must have taken place 

 within that limited period. Such being the ascertained rate 

 of elevation in the Red River Valley, it is altogether probable 

 that the rise in the land at North Bay would not occupy a 

 much longer period, for the conditions with respect to the 

 glacial ice and its recession are nearly alike in both regions. 

 In addition to this evidence adduced by Dr. Upham, I had 

 long before called attention to the small amount of erosion 

 which had taken place in the delta at Mattawan since the 

 glacial outlet there had been closed. 



Another independent line of evidence indicating the 

 brevity of the past life of the Niagara gorge is drawn from a 

 study of its width at the mouth. In 1898 and 1899 I was 

 deputed by the New York Central Railroad to study the lower 

 part of the eastern side of the gorge, to shed what light I 

 could upon the stability of the conditions surrounding the 

 road bed built along the face of the gorge. Every facility for 

 examination and measurement was granted me. Briefly, the 

 results were as follows: the width of the river at the mouth of 

 the gorge is 770 feet, which is practically the original width of 

 the gorge, for the debris falling down has prevented the stream 

 from enlarging its channel at the base of the cliff. 



Assuming that the cliff was originally perpendicular, 

 measurements showed that the strata at the summit bad 

 receded on the east side only to the extent of 388 feet, making 

 the total width of the top of the gorge at the mouth 1,553 

 feet, on the supposition that the west side had been worn 

 away as fast as the east side had been. But various irregulari- 

 ties prevented as accurate measurements on that side. Now this 

 subaerial erosion of 388 feet from the top of the gorge on one 

 side indicates the removal of an inverted section of the face 

 of the gorge, with a base of 388 feet and a height of 340 feet, 





