18 
GLACIAL PERIOD. 
like those now covering Greenland. The 
easternmost ancient glacier of Switzerland 
was that of the Rhine. It had its sources in 
all the valleys from which now descend the 
many tributaries of that stream, and must 
have spread over the northeastern Cantons, 
filling the Lake of Constance, and terminating 
at the foot of the Suabian Alp. Next to the 
glacier of the Rhone, this was once the lar¬ 
gest of those descending from the range of the 
Alps. 
West of Mont Blanc, Professor Guyot has 
traced the boundaries of two other distinct 
ancient glaciers. One of these, the glacier of 
the Arve, followed chiefly the course of the 
Arve, and, though discharging the icy accu¬ 
mulations from the western slope of Mont 
Blanc, was, as it were, only a lateral affluent 
of the great glacier of the Rhone. The other, 
the glacier of the Isere, occupied, to the south 
and west of the preceding, the large triangular 
space intervening between the Alps and the 
Jura, in that part of Savoy where the two 
mountain-chains converge and become united. 
It would lead me too far, were I to describe 
also the course of the great ancient glaciers 
