\ 



6 THE ANTARCTIC HORST 



The most clearly defined of all the cross faults, which mostly ti'end east and west, 

 is that which runs eastward from Erebus through Mounts Terra Nova and Terror. 

 Westward the same fault may pass a little to south of west through Cape Barne to the 

 Ferrar Glacier Valley, or to Dry Valle}' immediately to the north. Minna Bluff and 

 Mount Discovery are situated on an E.S.E. and W.N. W. fracture. Cape Washington 

 and Mount Melbourne are also on an E.S.E. and W.N.W. line. The remarkable 

 straight coast, bounding Lady Newnes Bay on the north, probably represents an 

 E. and W. fracture. 



It will thus be seen that the chief centres of recent volcanic eruption in the Ross 

 Sea region and South Victoria Land ai'e the nodes of the meshes of a network of 

 faults. 



The position and direction of throw of the chief faults is shown on the accom- 

 panying map. 



The details of the Antarctic Horst from Mount Melbourne to Minna Bluff are 

 given on Plate HI. 



It will be seen from the three sections across the main ranges (Fig. 67) 

 that, both to the west of the Queen Alexandra Range, the Royal Society Range, 

 and Mount Nansen, the inland neve fields do not rise to the level of the moun- 

 tains of the Horst, falling short of it by about from 1000 to 2000 feet (305-610 

 metres). 



It may be added that the plateau character of the Western Mountains is 

 preserved — as far as the southern party under Shackleton could see — for a 

 considerable distance to the south-east of the Beardmore Glacier.* Northwards the 

 plateau sandstones extend at least as far as Mount Nansen, a distance of about 800 

 miles (1299 kilometres). 'J'his plateau sandstone has been proved to be coal-bearing 

 in places. Both it and the old peneplain, upon which it rests, are traversed by huge 

 sills of quartz-dolerite or diabase analogous to the sills of the Karroo in South Africa, 

 and to the gigantic quartz-dolerite sills of Tasmania. 



Physiographically it is difiicult to estimate the age of the Antarctic Horst with 

 any approach to accuracy. The great horst, as a whole, has not been seriously 

 reduced by erosion since its inception as the result of faulting. Provisionally it may 

 be concluded that these ranges show signs of adolescence rather than of either youth 



or of maturity, t 



Peneplains. There is strong evidence of the horizontally bedded plateau sandstone, 

 the Beacon Sandstone, having been deposited upon an ancient peneplain of crystalline 



* The photograph of Mount Fridtjof Nansen, 15,000 feet above the sea, published by Amundsen 

 ("The South Pole," vol. ii., facing page •'iO) proves the plateau rocks to extend for at least 190 miles S.E. 

 of the Beardmore Glacier. 



t The fact must be emphasized that the great outlet valleys of the Antarctic have been cut down to 

 depths of from 5000 feet to 8000 feet below the general original level of the plateau, that their width is 

 from a mile up to about 15 miles, and their length from 30 to about 100 miles. Thus the Horst has been 

 deeply dissected. 



