THE ANTARCTIC HORST 6 



deeply trenched in places by corrie glaciers, is on the whole but little reduced by 

 erosion. In this connection one must bear in mind the protective action of ice and 

 snow, so ably advocated by Professor Garwood.* The effect of this protection is to 

 prolong the youthful appearance of a landscape, which, tested by the time-unit of a 

 temperate, as opposed to a polar climate, might be said to have arrived at maturity. 



The classification of this coast-line is discussed in the last chapter of this memoir 

 dealing with the relation of Antarctica to other parts of the world. 



The Antarctic Horst. If we now return to the main coast-line on the west, the 

 land next to the coast is seen to have the form of an immense elongated horst, from 

 50 to 100 miles (180 to 160 kilometres) in width, bounded eastwards by faults, 

 having a throw of at least 6000 feet (1829 metres) and westwards by faults throwing 

 probably about 2000 feet (610 m. ). This horst forms a gigantic retaining wall, damming 

 back and so causing a higher piling up of snows which fall upon the plateau to the 

 west. At intervals the horst is breached b}?- valleys, perhaps partly of tectonic origin 

 (in the beginning either synclines or trough faults, but greatly modified by subsequent 

 glacial erosion), which form outlets, "by-washes," or "spillways" for the surplus 

 inland ice and snow. The great N. and S. fault, near Cape Adare, is marked by 

 a volcanic zone extending southwards to Coulman Island, and striking thence, 

 through perhaps Franklin and Beaufort Islands, on to Mount Bird in Ross Island. 

 On this line is situated one of the most wonderful geysers in the world, which 

 occasionally bursts into eruption in sympathy with Mount Erebus. Thence, the fault 

 trends through Mount Erebus and the zone of craters near Hut Point, and on 

 through Black Island. Parallel to this fault, to the east of it, is a second fault, 

 which runs through Mount Terra Nova, White Island, and Minna Bluff. To the 

 west of Mount Erebas, and on the west side of McMurdo Sound, another strong 

 meridional fault is probably marked by the very steep-to coast. Tlie discovery in 

 the course of our geological investigations of included fragments of Beacon (?) sand- 

 stone in the lavas of Erebus is further proof of the existence of this fault, for whereas 

 under Mount Erebus the Beacon Sandstone t is presumably far below sea level, its base 

 is about 5000 feet above the sea in the mountains to the west of Erebus. Just south 

 of Minna Blufl' this fault is shifted westwards by a strong cross fault and trends 

 thence, first in a S.S.E., then in a S.E. direction. Noi'thwards from McMurdo Sound 

 this meridional fault following the coast trends northerly past the base of Mount 

 Nansen. The western shore of Lady Newnes Bay, and the straight coast to the 

 south of it, probably mark another fault intermediate between the Cape Adare line 

 and the Nansen line. 



* "Geographical Journal," vol. 30, 1910, pp. 310-339. 



t The term Beacon Sandstone, fir.st used by H. T. Ferrar, geologist to the National Antarctic Expedi- 

 tion of 1901-04, is here applied to all those more or less horizontally bedded strata, mostly sandstones, 

 which overlie in East Antarctica, the Pre-C'ambrian crystalline complex as well as the Archseocyathinse 

 limestones. For reasons stated in the concluding chapters of this memoir, their age at the base may be as 

 old as Devonian, and at the summit may be Jurassic or even Cretaceous. 



