244 COMPTE-RENDU. QUATRIÈME PARTIE 
basins of the iinevenly laid laler drift which are so strongly 
contrasted witli the smooth and attenuated outer portion of the 
drift sheet beyond the moraines. 
The wane and departure of botli tlie North American and 
European ice-sheets hâve been marked by many stag-es of hait 
and oscillation, whereby the flora, including forest trees, and 
less freqiiently traces of the fanna, of the temperate areas adjoin- 
ing the melting and mainly receding ice were covercd by its 
drift at the times of temporary re-advance of the ice-border. 
No better illustration of conditions favorable for the biirial of 
forest bcds in the drift can be imagined than those of the Ma- 
laspina glacier or ice-shcet, betwecn mount St. Elias and the 
océan, explored by Russell in 1890 and 1891, and found to be 
covercd on its attenuated border willi drift which supports 
luxuriant growing forests. Let a century of exceptional snow- 
fall cause a thickening and re-advance of that ice-sheet, and sec- 
tions of its drift exposed after the glacial recession will show a 
thick forest bed of chiefly or wholly temperate species. The 
vicissitudes of the general glacial retreat seem to me to hâve 
been due thus chiefly to variations of snowfall, some long tenus 
of years having much snow and prevailing cool température, 
thereforc allowiug considérable glacial re-advance, while for the 
greater part other séries of years lavored rapid melting and 
retreat. 
Under this view we may, I think, account for ail the obser- 
vations which hâve been licld in America and Europe as proois 
of interglacial epochs, without assuming that there was cithef 
any far re-advance of the ice-border or any epeirogenic move- 
inent attending the glacial retreat of siich magnitude as to iu' 
duce the lluctuations of which the forest beds and marginal mo- 
raines bear witness. Though the whole history of the wane of 
the ice-sheets is, indeed, very complex and long, as mcasured 
by OUI- familiar historical time units, it was yct, in my opinion, 
gcologically very brief, if compared with ail preceding géologie 
periods and epochs. The formerly supposed necessity of prcdi- 
cating long intcrglacial epochs seems to me a misunderstanding- 
Inslead, as Dana, Wright, Hitchcock, Lamplugh, Kendall, Fai- 
san, Holst, Nikitin, and many other glacialists believe, the Ice 
âge seems to me to bave been essentially continuons and single, 
with important fluctuations, but not of epochal significance, both 
during its advance and décliné. 
