GLACIAL DRIFT. 327 
fit the corresponding cases in Europe. In such case the name “inter- 
glacial” would still be applicable to them, although not in precisely the 
same sense in which the term is now understood. The preposition 
inter would signify a place between the two tills. These do not prop- 
erly represent two glacial periods: they are different accumulations pro- 
duced by a single ice-sheet, with a varying outer edge. 
LENGTH OF THE GLACIAL PERIOD. 
I desire to call attention to another feature of glacial history that has 
been overlooked. Granting that the cold period commenced 240,000 
years ago, as determined by the orbital changes, it does not follow that 
it terminated 80,000 years since, when the extreme eccentricity disap- 
peared. The conditions would have been analogous to the state of 
things observed every year in our climate. The extremest cold of win- 
‘ter does not occur at the shortest day, but fully six weeks later, while 
the snow may continue till the first of May, though usually disappearing 
by the middle of April, so the great glacial winter would not have termi- 
nated with the end of the cycle. The prodigious quantities of ice and 
snow covering the northern latitudes would not have allowed the return 
of spring for many thousand years. If we were authorized to compare 
directly the annual duration of winter after the shortest day with this 
glacial period, it would be possible to fix the date of the disappearance of 
the ice. About one fourth part of our year elapses between the winter 
solstice and the vernal equinox. A fourth part of the long glacial winter 
would be 40,000 years. This would bring the close of the glacial, or, 
better, the Champlain period, to an epoch 40,000 years ago. If there is 
any variation from this estimate, it appears as if the subsequent period 
would have been shorter rather than longer, because of the enormous 
quantity of ice to be melted. 
The description of the events occurring in the Champlain period, such 
as the deposition of the kames and terraces, shows that the time of melt- 
ing need not have been greatly prolonged. The kames, being laid down 
immediately underlies them in being less hard and tough. It is often sandier and more frequently contains very 
large blocks and boulders, while at the same time its included stones and boulders are not so universally well 
smoothed and striated—or, to express it otherwise, angular unpolished stones and boulders are more common in 
the upper than in the lower mass of till. Again, I may note that the intercalated beds often thin out so as to 
allew the upper and lower deposits of boulder-clay to come together.””—Geikie’s Great Ice Age, second edition, 
revised, p. 19. 
