88 
ICE-PERIOD IN AMERICA. 
the water’s edge, but beneath it, wherever the 
harder rocks have resisted the action of the 
tides and retain their original character. In 
our granitic regions intersected by innumera¬ 
ble trap dikes, as, for instance, at Nahant, the 
smooth surface of many of the rocks, where 
sienite and trap have been evenly levelled, 
shows that the same inexorable saw, cutting 
alike through hard and soft materials, has 
passed over them. In the hills of pudding- 
stone in the neighborhood of Roxbury we have 
quartz pebbles cut down to the same level with 
the softer paste in which they lie imbedded 
with pebbles of sandstone, clay-slate, gneiss* 
and limestone. In the limestone regions of 
Western New York and Northern Ohio, about 
the neighborhood of Buffalo and Cleveland, 
the flat surfaces of the limestone are most 
uniformly polished, furrowed, and scratched, 
the furrows often exhibiting that staccato grat¬ 
ing action described in a former chapter. I 
have observed the same traces in the vicinity 
of Milwaukee and Iowa City, and we know, 
from the accounts given by Arctic travellers 
of their overland expeditions, that these pe¬ 
culiar appearances of the surface are char- 
