Perry.] 88 [February 28, 
height it is evident that nearly the whole surface has been smoothed 
and more or less striated. Rising superior to this line of elevation 
there was no doubt a considerable mass of solid ice, and above this 
perhaps, as many infer, somewhat of névé and of unconsolidated 
snow. Some are of the opinion, and for this view there appear to 
be plausible reasons, that the surface of the great ice-sheet was 
much higher than the present summits of the White Mountains. 
The upper portion of the ice, even the last 2000 or 3000 feet, would 
be far less effective in wearing off and smoothing down an underly- 
ing rock surface than parts overlaid by a greater superincumbent 
mass. Be this, however, as it may, the least supposed thickness is 
comparatively great. If now we assume the ice-sheet to have been, 
_as Mr. Dana does, comparatively level on its upper surface, we are 
compelled to admit that it not only covered all the rest of New Eng- 
land, but that it also actually lay above what are now the highest 
summits of the Green Mountains which have glacial furrows, in a 
mass more than a thousand feet in thickness. it is not improbable, 
however, that the surface of the ice-sheet was somewhat lower to the 
south and to the south-east of the White Mountains than it was all 
along their flanks, and along the most elevated lineof the Green 
Mountain range. 
On the other hand, it seems probable that the height of the ice- 
sheet was very much greater still further to the north and to the 
north-west. So far as I am aware, every known fact- points in this 
direction. Jt would not perhaps surprise one to learn we may here- 
after discover decisive proof that there were many inequalities in the 
surface of the ice, and that between such elevations as the White 
Hills of New Hampshire and those of the Adirondacks there may 
have been slight, if not considerable, depressions. While these 
points are by no means certain, there seems to be good reason for 
supposing that the thickness of the ice-mass was immense. The 
agency that was at work certainly has left traces in New England 
little less than 6000 feet above the present level of the sea; and, in 
places lying further to the north, it may have reached, as some have 
inferred that it actually reached, even if it did not exceed, the height 
of eight or ten thousand feet. 
§ 10. Zhe Motion of the Ice-Sheet. 
If such a mass of ice as has been supposed actually existed it, of 
course, moved; not necessarily under the exact conditions, and with 
