EROSION BY GLACIERS 201 



Cirque structure was not studied in detail, but many fine examples of cirques 

 exist, as near Mount Chetwynd, and in the neighbourhood of the north-west side of 

 the entrance to the Beardmore Glacier, also at the north side of the Mawson 

 Glacier. * 



Hanging valleys have already been described in the Ferrar Glacier Valley in 

 this Memoir, and fine examples could be seen in the valleys to the north of Terra 

 Nova Bay. 



Steps or treads are well marked in the course of several of the outlet glaciers. 

 Their presence can only be inferred from the existence of numerous large ice-falls, 

 like that to the north of the Suess Nunatak in the Mackay Glacier Valley, where a 

 great rock-bar of quartz-dolerite crosses the valley almost at right angles. These 

 would seem to be developed, in the outlet glaciers, chiefly at the point where the 

 glacier ice, in course of its erosion, has reached the base of the Beacon Sandstone 

 formation, and is recessing itself into that formation, so that it brings down its 

 channel eventually on to the hard resistant rocks of granite, gneiss, &c. Such ice- 

 falls were met with by Captain Scott near the head of the Ferrar Glacier Valley, 

 above Depot Nunatak ; by Sir Ernest Shackleton near the great coal-measure and 

 limestone nunataks, Mounts Buckley, Bartlett, and Darwin. The Northern Party 

 also observed from a distance with field-glasses that there were immense ice-falls 

 some 30 to 40 miles inland at the head of the David Glacier, at the point where it 

 was recessing into the Beacon Sandstone of the plateau. Terraces were observed at 

 Ross Island, near Cape Bird, and at Backdoor Bay, as well as on the coast of 

 Victoria Land. They are very strongly marked at Mount Crummer, and much 

 has already been said about the shelf on which the great 23iedmont of the eastern 

 side of the horst rests. The question as to what extent these terraces are due to 

 marine erosion, glacial erosion, or the effect of running water has already been 

 discussed. 



The subject of the glacial erosion of lakes has already been described in detail 

 in the section of this work dealing with lakes, where it has been pointed out that 

 in the neighbourhood of Cape Royds there is good evidence of rock basins having 

 been scooped by ice action to some distance below sea-level. This is notably the 

 case with Sunk Lake near Cape Barne. Deep Lake, Blue Lake, Clear Lake, and 

 Coast Lake are obviously rock basins scooped out of the solid rock by glacier ice. 



* A special study of cirque structure has been made by Mr. T. Griffith Taylor, of Captain 

 R. F. Scott's recent Antarctic Expedition, between the Mackay and Koettlitz Glacier regions, and by 

 one of us (R. E. P.) to the north of the Reeves Piedmont. These results have partly been published in 

 "Scott's Last Expedition," vol. ii., partly in the Geograjihical Journal for 1914. In the latter jjaper 

 Mr. Taylor argues for the formation of outlet glacier valleys by cirque (cwm) erosion, obviously a 

 possible origin. The facts should not be lost sight of (1) that the outlet valleys may be partly tectonic 

 in origin ; (2) that even if the Antarctic Horst post-dates Lower Miocene time when river erosion 

 dominated Antarctic relief, the sti'ip of the eai'th's crust occupied by the hoist may already have been 

 somewhat notched by river valleys previous to the faulting which produced the horst. 



