GLACIAL PERIOD. 
7 
There may have been a succession of cold 
summers, or, if now and then a warmer sum¬ 
mer intervened, a colder one followed, so 
that the glacier regained the next year the 
ground it had lost during the preceding 
one, thus continuing to oscillate for a num¬ 
ber of years along the same line, and add¬ 
ing constantly to the debris collected at its 
extremity. Wherever such oscillations and 
pauses in the retreat of the glacier occurred, 
all the materials annually brought down to its 
terminus were collected; and when it finally 
disappeared from that point, it left a wall to 
mark its temporary resting-place. 
By these semicircular concentric walls we 
can trace the retreat of the ice as it withdrew 
from the plain of Switzerland to the fastnesses 
of the Alps. It paused at Berne, and laid the 
foundation of the present city, which is built 
on an ancient moraine ; it made a stand again 
at the Lake of Thun, and barred its northern 
outlet by a wall which holds its waters back to 
this day. Other moraines, though less dis¬ 
tinct, are visible nearer the base of the Ber¬ 
nese Alps, and, above Meyringen, the valley 
is spanned by one of very large dimensions. 
