348 
Frank Carney 
which intervenes along all the lines of ice movements between ij 
the region under discussion and the dispersion centers of the ice. i 
The load which an ice sheet acquires doubtless depends in the : 
first place upon the irregularity of the surface over which the ice i; 
is moving, and in the second place upon the attitude of that sur- ' 
face in reference to the dispersion area: that is, ice moving down j 
a slope does not perform the abrasive work conducive to the I 
acquirement of a great amount of debris, whereas ice moving !|i 
against a slope is apt to take on much more rubbish. The litho- | 
logical aspect likewise of the country being traversed is a factor |: 
of considerable importance. This factor enters into the question f 
in two ways: (i) Stratigraphical terranes that are easily denuded 
either by erosion or by abrasion suffer more from an ice cap than !i 
do terranes that because of structure are less easily influenced by j 
these agents. ( 2 ) On the other hand, the attitude of the rock { 
formations regardless of the general slope of the country is a I 
control in the acquirement of a load by glacial ice. In much the j 
same manner, but to a less degree, the abrasive work of ice is 
accentuated when the movement is against the dip of the rock. : I 
It has been noted that on coasts where the rocks dip seaward, ; 
wave work is less effective. The analogy between the erosion of ; 
waves and ice may not be close; nevertheless there is^a similarity h 
in the mechanical principles involved. 1 
It is apparent, therefore, that a cross-section of the ice sheet | - 
transverse to the axis of movement would reveal an irregular dis- 
tribution of debris. This irregularity is due largely to the factors ' : 
already discussed, that is, the topography, and the attitude and |( 
structure of the rocks over which the ice has moved. If the local i 
topography were not a factor in the final disposition of drift by |li 
an ice-sheet, then any given moraine of an area would be the 1: 
counterpart of the termini of the lines of rubbish carried by the I - 
ice at the time of that halt. ; 
This consideration as yet has neglected the fact that ordinary 1 
ground moraine is the sum total of debris in the ice that finally 1 
covered the area of this moraine. The ideal example of such : 
drift-accumulation is seen only when some portion of an ice-sheet 1 ■ 
becomes stagnant and decavs. Then the load of drift in this | 1 
stagnant ice will have, after melting, about the same areal dis- 
tribution that it had when enclosed in the ice. So it follows that ( 
a considerable area of detached ice might be marked by an accu- ^ 
