Perry.] 92 [February 28, 
of motion was very far less than even that stated by Mr. Dana,—say 
from ten to fifteen feet a year. But in making an estimate of this 
kind, a great many elements need to be taken into account—too 
many for present consideration. It may be simply remarked, there- 
fore, that the motion of the ice-sheet, like that of an existing glacier, 
was undoubtedly very unequal in different parts. Indeed, on this 
point I have already found conclusive evidence.t In some portions 
of. the mass, there were plainly accelerations; while in others, the 
ice necessarily met with obstructions, and was thus in a greater or 
less degree retarded. 
§ 11. The Direction of the Ice-Sheet 
Is indicated by a great number of facts, which need not be enu- 
merated. It is easily made out in an uneven region by the charac- 
teristic aspects of what are called the stoss and lee sides of the rocks. 
Like horizontal and vertical isotherms, the phenomenon was to a 
considerable extent climatical. Accordingly, it must have been 
largely determined by the climatic conditions of moisture, tempera- 
ture, and the like; meanwhile it was partially, and in some places 
greatly, modified by the general contour and the everywhere varying 
features of the country. In the earlier staves of the work, before 
the masses of ice were very thick, and while they mostly lay in dis- 
tinct and separate depressions, the direction of each sloping valley 
would be that of its ice-stream ; so that, moving along in their chos- 
en channels, the several glaciers must have denuded, polished and 
striated the surfaces of the rocks over which they passed, thus leaving 
vestiges of their existence, of their work, and of the course they 
took down the valleys which they traversed. Such traces, had there 
been no subsequent abrasion, would have remained to tell us, no 
doubt explicitly, the direction of the local glaciers during the earlier 
part of the ice period. 
On the increase of these local glaciers, and the final union of all 
in one immense sheet, a marked change appeared not only in the 
11 may refer to a single item of evidence pointing in this direction. The obser- 
vations which I have made clearly indicate that travelled matter has been trans- 
ported to a much greater distance in the comparatively level basin of the 
Mississippi than in the rough hilly country striking the eastern border of the con- 
tinent. Itis not improbable that a like comparison would hold true between the 
drift of this great basin and that of the mountainous region lying along its north- 
ern border. Similar testimony is found, only it is on a smaller scale, in the basin 
of the Connecticut, and in that of the Housatonic, to mention no other instances. 
