Ice Afje hi Xorth America and Europe. — Upfiam. 107 
other northwest of Hudson bay, as shown by Tyrrell's obser- 
vations,* and a third upon the northern part of British Colum- 
bia. From my studies of the glacial lake Agassiz, whose du- 
ration was probably only about 1,000 years, the whole Cham- 
plain epoch of land depression, the departure of the ice-sheet 
because of the warm climate so restored, and most of the re- 
elevation of the unburdened lands, appear to have required 
only a few (perhaps four or five) thousand years, ending 
about five thousand years ago. These late divisions of the 
Glacial period were far shorter than its Kansan, Aftonian, and 
lowan stages; and the ratio of the Glacial and Champlain 
epochs may have been approximately as ten to one. The term 
Champlain conveniently designates the short closing part of 
the Ice age, when the land depression caused rapid though 
wavering retreat of the ice border, with the accumulation of 
many retreatal moraines of very knolly and bowldery drift. 
How THE Ice-sheet formed Marginal Moraines, 
One difficulty which will arise in the minds of many glacial- 
ists, concerning the brevity of the time allotted to the Wiscon- 
sin and later moraine-forming stages should receive special 
consideration. The view here presented, with the light de- 
rived from my work on lake Agassiz, implies that the con- 
spicuous belts of morainic hillocks, hills, and ridges, consisting 
of veiy bowldery till, frequently with much kame gravel and 
sand, of which I have mapped twelve in Minnesota and North 
Dakota, and Leverett a still larger number in Illinois, Indi- 
ana, and Ohio, were each amassed within a few years, or at 
the longest probably no more than 25 or 50 years, even for the 
accumulation of the prominent Leaf hills, rising 200 to 350 
feet above the surrounding country. How could such rapid 
drift transportation and dejjosition take place? If this ({ues- 
tion can be satisfactorily answered, with reference of the mo- 
raines both in North America and in Europe to the time of re- 
treat from the lowan glacial boundaries, a chief argument, 
which is much relied on by the def<'nders of the theory of two 
or several distinct glacial epochs, having unlike methods of 
drift accumulation, will be set aside. 
*Geol. Magazine, IV, vol. i, pp. .394.39!), with map, Sept., 1894: Am. 
Geologist, vol. xiv, pp. ,338-340, Nov,, 1894. 
