276 The AmericAin Geologist. May, i895 
Records of the Drift chiefly limited to the Culmination 
AND Departure of the Ice-sheet. 
Nearly or quite all the other observations of interglacial 
beds on this continent seem more probabi}'' referable to the 
interval between the Kansan and lowan stages of extending 
glaciation, near the middle of the lee age, and to fluctuations 
of the general glacial retreat in the declining Wisconsin stage, 
of which successive steps or substages are indicated by boun- 
daries 2 to 7 on plate X. We are not, however, to infer there- 
fore that alternate decrease and increase of the ice-covered 
area were more prevalent during the decline than during the 
oncoming of the Ice age. Extensive glacial erosion and deep 
drift deposits have destroyed or concealed the far greater 
part of the records of the beginning and advance of this pe- 
riod to its Kansan stage of culmination. The earlier half of 
its history is mainly lost. All the moraines, eskers, kames, 
and valley drift, nearly all the interglacial deposits, and most 
of the striation preserved on the bed-rocks, belong to the later 
Kansan time of maximum extension of the ice-sheet upon the 
interior portion of our continent, and, in much larger measure, 
to its renewal of growth in the lowan stage and to its final 
recession.* 
Boreal and Arctic Species probably characteristic of In- 
terglacial Deposits during the Epoch of 
general ice accumulation. 
The conditions producing the abundant snowfall and the 
resulting ice-sheets of the Glacial period were undoubted!}'- 
attended with southward and outward migration of many bo- 
real and Arctic species of animals and plants, which during 
the Tertiar}^ era had come into existence in the polar regions 
and on high mountain ranges reaching to altitudes of prevail- 
ing cold in more temperate latitudes. Accepting epeirogenic 
uplifts of the portions of the earth's crust enclosing the North 
Atlantic ocean as the cause of the envelopment of the conti- 
nental areas on each side by the Pleistocene ice-sheets, we 
shall readily see how the cold-loving circum polar and alpine 
fauna and flora of preglacial times would spread outward over 
*C()mpjin' tho Tweiily-second Annual Report of tlie Geol. Siu'vey of 
Minnesota, for 1893, pp". 34. 41: bulletin, Geol. Society of America, tliis 
vol. VI, p. 21; and Prof. T. C. Cliamberlin, in "The (ireat Ice Age'" (J. 
Geikie, third edition, 1894), pp. 753, 754. 
