186 BULLETIN OF THE 



surface as they were urged forward ; others were lifted into the body of 

 the ice. Thus there wei-e 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 

 large 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 dii"ected. 



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 debris 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 



