192 SOME GEOGRAPHICAL NOTES, ETC., 



not unlike the steep valley which leads from Fenton Hut 

 down the outer slope of the Plateau towards Russell Falls. 

 There was, therefore, a good deal of material to be removed 

 during the Ice Ages before these valleys developed the 

 characteristic cirque-heads of to-day. 



In each of these three typical cases the cirque has a 

 maximum wall of about 1,000 feet, lying approximately be- 

 tween the 3,000 and 4,000 feet contours. 



It is further to be noted that these cirques lie largely 

 on the sheltered easterly aspect of the ridges, so that they 

 are protected from the hot afternoon sun. 



To understand the way in which the ice has eroded 

 these valleys we must, I think, further consider two aspects 

 of the problem. Firstly, the alimentation of the glaciers; 

 and secondly, the life history of the latter. We shall then, 

 I believe, see that nivation probably played a more important 

 part than planation in carving out the main cirques. This 

 type of erosion also helps to explain the interesting shelf- 

 tarns above Lake Seal, and the unusual position of Lake 

 Belton ^'perched" above Lake Belcher. 



The snow-fields nourishing the glaciers of the plateau 

 must have been very circumscribed. The collecting ground 

 for the Hayes and Belcher glaciers was the original K Col 

 and the adjacent narrow ridges. It seems to me unlikely 

 that the Belcher glacier resulting from this meagre snowfield 

 had sufficient power to gouge out a bowl-shaped hollow right 

 at its head to the depth of one thousand feet. The same 

 objection applies to the Hayes glacier, and to a lesser degree 

 to the Seal glacier. 



On the other hand, if we adopt the principle of nivation, 

 as developed by the Americans, Matthes, Johnson, and Hobbs, 

 the process of erosion becomes much more intelligible. In 

 nivation the alternating freezing and thawing of water in 

 the interstices of the rocks is the prime agent of disinte- 

 gration. The glacier plays a somewhat passive part in the 

 erosion, but supplies much of the water for the nivation by 

 the melting of its periphery. Its surface, however, acts as 

 a vehicle which very slowly carries away debris to the lower 

 end. The thaw-water streams at the side of the glacier also 

 are of great importance in eating down the rock edges of 

 the valley. The glacier also acts something like the scour- 

 wall at a river mouth which directs the removal of debris. 

 (See the paper on Antarctic Glaciology by the writer — 

 Geogr. Jnl., 1914, p. 562.) 



