Perry.) 106 [February 28, 
that one result of the movement of the ice-sheet was “the taking up 
of the sand or gravel, stones and rocks, thus separated or dislodged 
into its own mass, which it was enabled to do because of the attend- 
ant breaking of the ice .. . and the readiness with which ice becomes 
solid again by regelation. . . . Thus the glacier moved slowly on, en- 
gorging itself with whatever loose material it made, as well as with 
what it found in its path.”’? He accordingly appears to think that the 
matter disengaged from the inferior rocks by the action of the ice- 
sheet, was lifted up into its body, more or less diffused through it, 
and of course not distributed until its final thawing. Now this view, 
so far as I am aware, has no countenance from facts; none from 
the best observers of existing glaciers;? none from theoretical 
considerations. While the glaciers of the present rest upon the 
drift proper, and are themselves masses of pure ice, with the 
exception of the sands blown over their surfaces, and the mate- 
rial of lateral and medial moraines, such must have been still more 
the case, during the middle and main portion of the Glacial times, 
when there were only afew solitary peaks, from which superficial 
material could have come. 
IT may accordingly resume the statement, that there was necessa- 
rily not a little detritus beneath, and somewhat of it in front of the 
great glacial mass; and that this would be left, to a very large extent, 
in its confused condition, on the final wasting of the ice. Now this 
great accumulation of matter, known as typical drift, remains as an 
existing witness of the work done, and of the time consumed in the 
process. While it is true that considerable portions of this hetero- 
geneous jumble have been removed, all that part of it which is now 
found above the valleys,as should be clear, belongs to the Middle 
Glacial times. Remembering that there is no evidence that any 
appreciable amount of detrital material was taken up into the body 
of the ice from beneath, or in any wise enfolded in it, one can see 
how difficult it must have been for the glacier to plough the underly- 
ing rocks with rapidity, or to any great extent in a short time, es- 
pecially during the later portions of its existence. Thus the abra- 
sion, after its first inception, must have been very slow; meanwhile 
the quantity of matter which was disengaged from the underlying 
1 Paper cited, p. 51. 
? Professor Agassiz informs me, that the mass of a glacier consists of pure ice, 
wholly free from detrital matter, and the same is the testimony of other and later 
observers of glacier-phenomena. 
