Geology and Natural History. 153 
by crevasses that the melting waters almost immediately plouge 
to the bottom. But as we go backward toward es line of perpet- 
ual snow, where the ice is thicker and the melting less rapid, 
we find streams upon the a “oe length epeodins upon the 
extent of ice free from crevass How far do these ac ae 
a? 
represent those of the great glacier of eastern North Am 
ithout some limitation, it is doubtful if the nctulagited ‘of any 
modern glaciers, even of Greenland glaciers, can be admitted as 
valid in the case of the great ice-sheet. The Greenland glaciers 
do not wholly overlap lars ge areas like the great ice-sheet, but here 
_ and there peaks emerge from them which form crevasses and assist 
the waters to pass beneath the glacier. However, waiving these 
phiscitoda and admitting for the time that. the aa streams 
of our great glacier were as well developed as those of the Green- 
land glaciers of to-day, at the same time we must admit that the 
surface streams were as well developed. Now the ails ees 
the ice-sheet at a proper distance north from its term It. 
should be noted that this is the condition of the Contalana Ttaciade 
during a time of comparative stability, or, quite probably, of 
their slow increase in extent and depth. 
But what would happen during the final melting of the ice-sheet ? 
All substantially admit that this melting was ver rapid and that 
it took place upon a great width simultaneously, although the ice, 
being thicker toward the north and in a colder mean climate, 
would not become melted so cues as farther south. As 
elsewhere Big min a no southward mouon would be possible 
e- 
of hills. Nowhere except in the White Mountains have I found 
traces of glaciers following local valleys. Apparently, almost all 
flow ceased after the melting had so far proceeded that the hills 
appeared above the i ice, Unde er these conditions no new lines s of 
began toemerge. The melting t took place so rapidly, and the mo- 
o 
cial streams nabs reached the ground. he te t of the area of 
sub-glacial streams must have lain south of the ced coast-line. 
he “glacier Sar bi ah into the Gulf of Maine, and off its front 
ve probably numerous boiling springs of fre sh water, like those 
t the submerged extremitice of the Greenland glaciers. The ice 
