8 VALLEYS OF THE HORST 



schists, gneiss, granite, slate, and altered limestone. A plateau of crystalline rock, 

 extending eastwards from the eastern base of Mount Lister for a distance of about 10 to 

 12 miles (18-19 kilometres) in width, appears to be a very ancient peneplain. This may 

 be a Pre-" Beacon Sandstone " peneplain, that is probably a Pre-Gondwana peneplain.* 

 This has been " re-discovered " by erosion in Cainozoic time. Its height above sea 

 level varies from about 4000 feet to 6000 feet. The figure below is a general 

 panoramic view from our winter quarters at Cape Royds on Ross Island, looking 

 westwards over 50 miles (80 kilometres) across McMurdo Sound to the Western 

 Mountains. 



Valleys. The Section, Plate V., shows the position and relative sizes of these 

 transverse valleys, mostly of the "outlet'' or Greenlandic type, which transect the 

 Antarctic Horst. 



The A^xlleys may be divided, broadly, into (1) outlet valleys, where they cross the 

 horst and form spillways for the inland ice reservoirs, and (2) alpine valleys, where 

 they do not completely transect the horst, and thus merely discharge glacier ice 

 formed within the drainage-area of the horst itself. These Alpine valleys have their 

 "thalweg" mostly athwart the long axis of the horst, but some are parallel to this 

 axis, like South Arm on the Ferrar Glacier, and the Mill, Keltie, and Hood Glaciers 

 of the Beardmore Glacier. These longitudinal (subsequent) Alpine valleys may be 

 in the first case of tectonic origin following fault planes parallel to the main lines of 

 faulting which bound the Antarctic Horst. Both types of valleys, outlet as well as 

 Alpine, have numerous hanging valleys emptying into them. 



The main valleys, especially the outlet valleys, offer such impressive examples of 

 ice-erosion as should convince even the most sceptical that glacier ice is able to carve 

 rock on a grand scale. They are mostly very steep-walled and either spurless or 

 with intensely faceted spurs. Details of these are given later in this report under 

 the head of Glaciology, where the question is discussed as to how far the valleys 

 are tectonic and how far glacial or flu'"irctile in origin. The interesting problem is 

 also investigated as to how far the glacial ice streams have brought their channels 

 to grade, the conclusion being that the channels are not by any means brought to 

 grade on the inland side of the great horst. If Antarctica were bared of its 

 snow and ice, extensive lakes would probably gather immediately to the west of the 

 horst. 



Plains. The steep coast of South Victoria Laud is subtended for about 200 miles 

 (319 kilometres) north wai'ds from the head of McMurdo Sound by a remarkable 

 plain. This is from 10 to 15 miles (16-24 kilometres) in width, and slojies up at a 

 gentle angle to a height of from about 1000 feet to 1700 feet (305-518 metres) to 



* In view of the resemblance of the lower portions of the Beacon Sandstone to the Devonian rocks of 

 the Falkland Islands, as explained in the last chapter of this volume, and especially in view of the recent 

 discovery by T. Griflitli Taylor and F. Debenham, of the late Captain Scott's expedition, of bony plates, 

 ascribed by Dr. A. S. Woodward to Devonian fish, this peneplain, in part at any rate, may be Pre-Devonian. 



