194 SURFACE GEOLOGY. 
phenomena" of this region have brought to light are briefly 
as follows : 
lst. In the northern half of this area down to the paral- 
lels of 389—409, we find, not everywhere, but in most local- 
ities where the nature of the underlying rocks is such as to 
retain inscriptions made upon them, the upper surface of 
these rocks planed, furrowed or excavated in a peculiar and 
striking manner, evidently by the action of one great de- 
nuding agent. No one who has seen glaciers and noticed the 
effect they produce on the rocks over which they move, 
upon examining good exposures of the markings to which I 
have referred, will fail to pronounce them the tracks of gla- - 
ciers.* 
Though having a general north-south direction, locally the ` 
glacial furrows have very different bearings, conforming in a 
rude way to the present topography, and following the direc- 
tions of the great lines of drainage. 
On certain uplands, like those of the Wisconsin lead re- 
gion, no glacial furrows have been observed (Whitney), but 
on most of the highlands, and in all the lowlands and great 
valleys, they are distinctly discernible if the underlying rock 
has retained them. 
2d. Some of the valleys and channels which bear the 
marks of glacial action—evidently formed or modified by 
ice, and dating from the ice period or an earlier epoch—are 
excavated far below the present lakes and water-courses which 
occupy them. 
These valleys form a connected system of drainage, at a 
lower level than the present river system, and lower than 
could be produced without a continental elevation of several 
hundred feet. A few examples will suffice to show on what 
evidence this assertion is based. 
* From oe my own observations | on the action of glaciers on ext i desse in. mne Alpe 
and in Oregon and 
could have produced such effects. A different view is — of this subject, it is true, 
but only by those r have never seen the markings 
in question. The track of a glacier is as unmistakable n that of a man or & bear. 
