ANTARCTIC GEOLOGY 317 



merit probably amounting to not less than 5000-6000 feet. The ice 

 of the hinterland is discharged to Ross Sea through a comparatively 

 small number of mighty glacier channels — ^ranging from 5 to 15 miles 

 in width and up to 100 miles in length — which breach the ranges at 

 intervals of many miles. 



This broad stretch from 50 to 100 miles wide, extending probably 

 for nearly 1000 miles in this quadrant and bounded on the east by 

 Ross Sea, has been appropriately named the Antarctic horst of South 

 Victoria Land. Whether the western rim where it descends to the 

 snow plateau is a zone of meridional fracture is still uncertain. The 

 occurrence of down-faulted blocks measuring many miles from 

 north to south along its eastern border has been inferred from the 

 physiography, while the presence of inclusions both of Beacon sand- 

 stone and of quartz dolerite in a parasitic cone on Ross Island sug- 

 gests that Ross Sea itself is underlain by the same formation. As 

 these rocks in the main horst in this latitude lie several thousand feet 

 above sea level, faulting on a very large scale with tremendous throw 

 is implied. The horst fractures are indicated by a volcanic zone ex- 

 tending from Cape Adare at least to the region of 78° S., where the 

 active volcano Mt. Erebus (13,300 ft.) forms the dominating fea- 

 ture of a cluster of mountains which rise from the sea in front of the 

 range. 



The explorations of the Mawson expedition have yielded much 

 information as to the nature of the outer arc of the Australian Quad- 

 rant west of South Victoria Land. The region along the Antarctic 

 Circle westward to 90° E. is now shown to be continuous land and 

 forms King George V Land, Adelie Land, Wilkes Land,^ and Queen 

 Mary Land. 



Adelie Land takes shape as a huge ice-covered plateau rising 

 rather steeply from the coast and reaching a height of 6000 feet at 

 a distance of 300 miles inland. The nature of the basement rocks of 

 this portion of the quadrant shows that the region is geologically 

 similar to South Victoria Land, both forming integral parts of a single 

 tectonic unit. 



Owing to the work of numerous British expeditions, the geology 

 of the Australian Quadrant can now be said to be moderately well 

 known. This geological structure is summarized in the synoptic 

 statement which follows. 



Lower pre- Cambrian 



Paragneisses, schists, crystalline limestones, calc-silicate rocks. 

 Orthogneisses, granite gneisses, charnockites, amphibolites. 



Upper pre- Cambrian {or Lower Paleozoic) 



Slate-graywacke formation of Robertson Bay. 



Younger granites, sphene-bearing diorites, lamprophyres, porphyries, etc. 



2 See (editorial) footnote 3 to Sir Douglas Mawson's paper above. — Edit. Note. 



