THE ANTARCTIC HORST 301 



folded, the strata, as described by Dr. Nordenskjold and Gunnar Andersson, dip 

 steeply in various directions. On the north-west coast of the American Sector of 

 Antarctica folded quartzite-like beds, discovered in a group of small islands 

 S.S.W. of Cape Roquemaurel, dip at 30° to north-west. At Cape Kjellman, half- 

 way between Cape Roquemaurel and Cajje Gunnar, sedimentary beds dip vertically 

 with a trend from south-west to north-east, that is, parallel to the coast, but on 

 the whole the dip appears to be in a general south-easterly direction. 



The folded strata of Hope Bay contain well-preserved plants of Jurassic Age, such 

 as Cladophlebis, Alethojiteris, Pterophyllum, Araucarites, &c. (the full list is given 

 a little later on). There is, therefore, clear evidence that here the Jurassic rocks 

 are strongly involved in the folding. 



At Snow Hill Island, also on the American side of the Antarctic, to the S.S.W. 

 of Joinville Island, Cretaceous and Tertiary rocks have been described by Nordensk- 

 jold and Gunnar Andersson. These dip towards E. and E.S.E. at gentle angles. 



So far as the South Polar and Ross Sea end of the great horst is concerned, it 

 would seem then to be a region of block faulting rather than a region of folding. 

 By far the heaviest downthrow is towards the east in this area. In fact all that 

 portion of the Antarctic continent, lying to the east of Ross Sea, and through to 

 Charcot Land, appears to have undergone heavy inthrows. The Ross Sea itself is 

 evidently a large senkungsfeld. The recent discovery by Amundsen of a range, 

 from 2000 to 4000 feet in height, trending north-easterly from a spot some 30 or 40 

 miles to the south-east of where he struck the mountains of the horst in 86° S. lat., 

 suggests that this important senkungsfeld does not extend across the horst itself 

 to Weddell Sea. 



In the next place, as regards the tectonics of Antarctica, one has to bear in 



mind the important fact that although the rocks of the horst, from near the South 



Pole to Cape Adare, are not known to have been faulted since Jurassic time, 



they are connected with an active volcanic zone which probably extends along 



the whole length of the gi-eat horst, and joins the active volcanoes of the American 



Sector and of the adjacent islands. No undoubted volcanoes have been identified 



as yet in the horst south of Mount Discovery, 78° 22' S., and Mount Morning, 



78° 30' S. The mountains known as Goorkha Craters, in lat. 78° 50' S., on the 



west coast of the Great Ice Barrier, are not known with certainty to be volcanic. 



The volcanic zone is known to extend at all events from Mount Morning to near 



Cape Adare, a distance of 450 miles, and if the Balleny Islands are situated on 



the same zone, the chain extends for a further distance of about 220 miles, in all 



670 miles. On the American side of the Antarctic the volcanic zone is known to 



extend from the Seal Islands to Bridgman Island, a distance of about 300 geogi-a- 



phical miles. No trace of volcanic action was observed on the western side of the 



American end of the great horst on the recent expedition of the Pourquoi Pass. 



One of the greatest ditficulties in correlating the trend lines of the great horst 



2 Q 



