426 
SCOTT'S LAST EXPEDITION 
the snow and ice mantle. This implies, I think, that 
the precipitation in the south-west corner of McMurdo 
Sound is extremely little, and increases both north- 
ward and southward. The most striking feature in 
the harbour — the Ice Tongue — has been described in the 
narrative. . The Mackay Glacier moves 3 feet a day, 
as already recorded. Mention must be made of the ridge 
separating the new glacier from the Devil's Punch Bowl, 
This has certainly been covered quite lately by the new 
glacier. The harder dykes are striated, but the ridge is 
for the most part covered with granite debris. There is 
practically no englacial rock debris in the glacier, so that 
one is led to the important conclusion that the floor of 
the new glacier is covered with rock debris and that no 
erosion is taking place under this fairly large glacier. 
What was the floor of the Mackay Glacier at its period 
of greater area is exposed in many places 1000 feet above 
the sea ice in the form of rock-strewn plateaux. 
One of the most interesting features is the evolution 
of the cwm which is indicated on all sides in the steep 
facetted slopes. On Discovery Bluff are the couloirs or 
chimneys ; on Mt. England these become somewhat 
funnel-shaped ; on the face of the Kar Plateau they deepen 
to a definite if shallow bowl. They obviously only ori- 
ginate on steep slopes where the icy covering is shallow. 
Avalanche Bay and the Devil's Punch Bowl are respec- 
tively filled and empty cwms, both at sea level. Along the 
southern crest of the valley are giant cwms each with its own 
glacier. Here the Miller Glacier has cut through the divide 
and links the Mackay presumably to the upper Debenham 
