GLACIAL DRIFT. 32/ 



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 

 allow the upper and lower deposits of boulder-clay to come together."— Geikie's Great Ice Age, second edition, 

 revised, p. 19. 



