680 LT. Cs CHAMBEREMN: 
reason to believe that the rate of supply from the interior was 
greater than the average on account of crustal disruption and 
volcanic action. There seems, therefore, little ground to think 
that the glaciation should have followed closer after the 
elevation than it seems to have done. It would seem rather 
that the hypothesis was~ happy in this time relation at 
least. 
With most geologists, I doubt not, the chief question will be 
whether the postulated agencies could cause the glacial oscilla- 
tions, involving the removal and reproduction of the ice, in 
large part or in whole, as rapidly as the field evidence requires. 
Present measures of glacial rates and times are quite uncertain 
but not indefinitely so. Some rude approach to their value may 
be attained. Recently expressed opinions regarding the time 
since the last ice retired from the site of Niagara River, and 
inaugurated the erosion of its gorge, lie between 7000 and 
33,000 years, which we may average at 20,000 years. I place 
no special confidence in this figure, but it is rudely representa- 
tive of the average order of magnitude of expressed opinion. 
This represents only a part of the time since the beginning of 
the deglaciation that removed the Wisconsin ice-sheet. Accord- 
ing to Taylor’s views it would be only a very small part. 1 
doubt if any careful geomorphic geologist familiar with all the 
phenomena involved would seriously consider an estimate that 
made it much morer than one half ‘at the  *most4 so mthateant 
would apparently not be straining the evidence to take 40,000 
years as a rude measure of the time since the beginning of 
the retreat from the outermost moraine of the Wisconsin 
stage. However, this may probably be cut in half and halved 
again without over-straining the possibilities of the hypoth- 
esis. 
This is the time of retreat. An interglacial epoch involves 
not only the time of retreat, but the time of interglacial mildness 
and the time of re-advance. The best specific data now avail- 
able in America for estimating these elements are undoubtedly 
those afforded by the excavations about Toronto which have 
