21C> Hie American Geologist. April, 1896 
nated over the vertical pressure thai the ice tended to arch 
over the lee slope instead of flowing down it. Under the 
greater vertical pressure and lower velocity of the central 
areas the ice will hug the lee slopes more closely and they 
will be more generally glaciated. Jn this case, however, as 
truly as in the first, the ice in the lee must drag, that is. move 
more slowly than the ice above it ; and this retardation will 
almost inevitably, according to Chamberlin's Greenland ob- 
servations, lead to Hexing or shearing and the absorption of 
detritus. We are thus brought to the conclusion that from 
the summit or crest of nearly every elevation with an abrupt 
lee slope a stream of detritus flowed onward and upward into 
the Pleistocene ice-sheet during its progress over the land. 
And it is obvious that, if this view be even measurably sound, 
the mechanism is provided for the abundant transfer of drift 
from a subglaeial to an englacial position. This important 
conclusion may be presented in another way. The detritus 
urged up, or worn from, the stoss slopes by the movement of 
the ice clearly did not descend the lee slopes under the pres- 
sure of the ice, else these slopes would not be unglaeiated; 
therefore it must have passed on into the ice, or else have ac- 
cumulated in a passive form on the lee slopes. It was prob- 
ably disposed of in both these ways; but it is well known 
that stoss slopes are quite as likely as lee slopes to be encum- 
bered by ground moraine. 
The recently published experiments in ice motion made 
with wax by E. ('.Case,* have a special interest in this con- 
nection. They tally very closely with Chamberlin's Green- 
land observations, and materially strengthen our general 
conclusion that the forward motion of the ice over an uneven 
topography gives rise to obliquely ascending currents, and 
that from the summits of elevations basal detritus is carried, 
not down the lee slopes but forward and upward into the 
body of tilt- ice. 
It must, however, be conceded by the englacialist that dur- 
ing the period of maximum glaciation for any area, when the 
ice was thickest and the vertical pressure had its maximum 
value, a large proportion of the drift reaching the top of stoss 
slopes probably remained in the bottom of the ice and was 
♦Journal of Geology, in, 918-934. 
