278 The American Geologist. May, 1895 
replenished. This process, after interruption b}^ the lowan 
stage of renewed cold and gathering of snow and ice on a 
large region of the Ohio, upper Mississippi, and Missouri 
river basins, gradually extended inward, giving steep gradi- 
ents of the ice-front which formed moraines whenever a series 
of exceptionally cool years and unusual snowfall allowed any 
pause or reiidvance. The whole ice-sheet, through the con- 
tinuance of its peripheral melting, disappeared; and mean- 
while the land on which it had lain, being unburdened, was 
moderately reelevated, in obedience to its law of isostasy, 
proportionally with the glacial melting and retreat. 
The Arctic plants and animals, which had flourished near 
the borders ^of the mainly increasing ice-sheet while the land 
liad its great preglacial altitude, could not endure the Late 
Glacial or Champlain depression of the land and then found 
refuge only on cold mountain summits, as of the White 
mountains in New Hampshire, which have about fifty species 
of otherwise solely far northern and ci re unipolar plants. 
Even closely adjoining the margin of the ice-sheet during its 
departure from the northern United States and southern 
Canada, the fauna and flora, as shown by the interglacial 
beds of Toronto and Scarboro' and of southeastern New 
Hampshire, marking temporary glacial retidvances, were pre- 
dominantly of the same species which are now found in those 
temperate latitudes. The warm climate which melted away 
the ice-sheet from these areas had principally banished the 
frigid and exclusively northern species and had brought back, 
as fast as the ice retreated, the vegetation and the animal life 
that have continued through the Postglacial period to the 
])resent day. P^vidence of such a general return of warm or 
temperate climatic conditions, near the boundaries of the ice- 
sheet while it was receding with occasional wavering oscilla- 
tions, is afl'orded by the interglacial beds of the upper Missis- 
sippi region and the north side of lake Ontario; and these 
conditions are now repeated on the border of the Malaspina 
ice-sheet. 
Previous to RusselTs observations of this Alaskan piedmont 
glacier, now being fast melted away, with its formerly engla- 
cial drift exposed by ablation on its outer part as superglacial 
