1872.) 99 | [Perry. 
stances, this may be estimated in connection with what are known 
as axes of elevation, portions of the beds having been_ removed in 
such a way that, in some localities, the exact amount can be deter- 
mined. In case the rocks in given places were peculiarly hard and 
unyielding, the glacial plough seems occasionally to have passed over 
them, scooping out the softer material, both in front and in the rear 
of these tougher parts. Thus to some extent, hills and valleys were 
formed in connection with the denuding agency, and remain to tell 
us of its extent. So lake-beds have been apparently deepened—-in 
not a few instances they were, no doubt, largely eroded and fash- 
ioned—by the action of moving ice. The same is true of river-chan- 
nels; they have been hollowed out and widened, the rocks having 
been deeply furrowed, seemingly by ice-streams. Pot-holes also 
occur at various levels and of considerable depth, which, so far as 
we can now see, could only have originated in connection with an 
immense ice-sheet. 
Reference may be made to a single locality, in which such pot- 
holes occur at a considerable height, in the basin of the Connecticut 
River. They are in Newfane, Windham County, Vt., near the crest 
of a hill, some 2600 feet above the ocean. While these pot-holes 
have been generally, if not universally adduced as the work of a tor- 
rent, it is difficult to conceive that a river, in the usual sense of the 
term, ever flowed in the place. In other words, the hill is isolated; 
whereas the descent of a stream upon it implies the existence of 
higher lands in the neighborhood, probably lying to the north; that 
such was the case, during the Ice-period, the face of the country 
affords no indications. Again, there is a valley, just below the pot- 
holes on the west, some 300 feet deep. This, if the explanation sug- 
gested be true, must have been eroded since their formation, and 
since there could have been opportunity for the flowine of an ordi- 
nary stream, to say nothing of a torrent, along the surface which 
they occupy. And surely to suppose that such erosion took place, 
and yet spared the pot-holes which were apparently as much ex- 
posed as the part of the rock removed, (and this is not a solitary 
case, for there are many like instances in different portions of the 
country, é. g.,in Oxford County, Maine,) is to make a heavy draft 
on our confidence, if it do not overtax the strongest credulity. 
Instead of resting in this unsatisfactory explanation, let us suppose 
that there was a great ice-sheet; that its motion was southward ; 
that it was of a thickness to cover, and that it accordingly passed 
