98 
ICE-PERIOD IN AMERICA. 
but these points are sufficient to give us data 
for the comparison. Mount Washington, for 
instance, is over six thousand feet high, and 
the rough, unpolished surface of its summit, 
covered with loose fragments, just below the 
level of which glacier-marks come to an end, 
tells us that it lifted its head alone above the 
desolate waste of ice and snow. In this re¬ 
gion, then, the thickness of the sheet cannot 
have been much less than six thousand feet, 
and this is in keeping with the same kind of 
evidence in other parts of the country ; for, 
wherever the mountains are much below six 
thousand feet, the ice seems to have passed 
directly over them, while the few peaks rising 
to that height are left untouched. And while 
we can thus sink our plummet from the sum¬ 
mit to the base of Mount Washington and 
measure the thickness of the mass of ice, we 
have a no less acccurate indication of its ex¬ 
tension in the undulating line marking the 
southern termination of the drift. I have 
shown that the moraines mark the oscillations 
of the glaciers in Europe. Where such accu¬ 
mulations of loose materials took place at its 
terminus, there we know the glacier must have 
