186 BULLETIN OF THE 
surface as they were urged forward ; others were lifted into the body of 
the ice. Thus there were two kinds of glacial wear: the one effected 
by the plucking out of large fragments which separated from the matrix 
along the lines of fracture formed by the bed or joint planes, and the 
other effected by the rubbing of the bits of stone against the firm set 
rock or against each other. 
4. That there were in certain places beneath the ice considerable 
streams of water moving between the overlying glacier and the firm set 
earth, these sub-glacial currents being in many cases competent to move 
Jarge quantities of detrital materials. 
The points above stated appear to me to be all which are of im- 
portance, and which have already been established in a conclusive way. 
The following problems as to the work done beneath glaciers seem to 
be worthy of consideration, and to their elucidation the matters set forth 
in this paper have been in the main directed. 
First. As to the rate of erosion on a surface of a given hardness 
during the passage over it of a given length of the ice sheet. 
Second. The relative amount of glacial erosion accomplished by the 
dragging out of fragments, and by the grinding action of such fragments 
upon one another and upon the bed rock. 
Third. The relative distance the above named classes of detrital ma- 
terials have been transported. 
Fourth. The lateral dispersion of the débris on its journey from the 
point of origin towards the ice front. 
Fifth. The relative amount of wearing of pebbles of diverse hardness 
in the course of their transportation. 
Sixth. The effects of pressure melting on the lower lying parts of 
deep glaciers, and the effect of such melting if it occurs in the process 
of erosion. 
This list by no means exhausts the catalogue of questions concerning 
the nature and effect of glacial movement. It contains, however, a sug- 
gestion of all the problems which it seems to me possible to deal with 
from the facts which are considered in this paper. In searching for a 
district in which to prosecute the above mentioned inquiries I sought to 
find a field where there should be some small, sharply limited area of 
rock, the material having a mineralogical character so distinct that it 
would not be possible to confound its waste with that from any neigh- 
boring locality. It was also necessary that the rock selected for study 
should be of sufficient hardness to insure it against speedy destruction 
in the rough conditions of glacial transportation. It is furthermore 
