378 THE GREAT ICE AGE 



for referring the Glacial age to a period so remote as that advo- 

 cated by Croll on astronomical grounds. Claypole has recently 

 discussed the matter at some length, and in a temperate spirit. 1 

 He takes the rate of erosion of the Niagara gorge as a measure, 

 and shows that the Falls of St. Anthony, as described by Win- 

 chell, and all the other falls and river gorges in North America, 

 give similar estimates, which are confirmed by the evidences of 

 lake ridges, of the rate of erosion, and of the conditions of 

 animal and plant life. The whole go to show that the culmina- 

 tion of the Glacial age may have occurred less than 10,000 

 years ago. He further shows that the differential elevation of 

 Lakes Erie and Ontario, the greater ease with which the river 

 could cut the lower part of its ravine, the probability that 

 the part of the gorge between the whirlpool and the fall was 

 not cut, but only cleaned out in modern times, and the possible 

 greater flow of water in the early modern period, all tend to 

 shorten the time required, and that, as Prestwich has inferred 

 from other data, and the writer also in various papers, some of 

 them of old date, the so-called post-glacial period, that of the 

 melting away of the ice, may come within 8,000 to 10,000 

 years of our own time. Probably the first of these figures is 

 the nearest to the truth, 2 so that, geologically considered, the 

 Glacial age is very recent. 



Still another question of great cosmic interest relates to the 

 possible alternation of glacial conditions in the northern and 

 southern hemispheres. There is evidence of drift in the south- 

 ern part of South America, similar to that in the north ; but was 

 it deposited at the same time ? If we could be sure that it was 

 not, many difficulties would be removed. The southern hemi- 



1 Trans. Edinburgh Geol. Soc., vol. v., 1888. 



2 Upham, one of the ablest and most experienced of the Glacial geolo- 

 gists in the United States, in a recent paper on the causes of the glacial 

 period, states similar conclusions, and adduces the evidence of Gilbert, 

 Andrews, Wright, Emerson and others in the same sense. 



