292 CAINOZOIC PAL.EOGEOGRAPHY 



last great glaciation, a divide existed, within the limits of the horst itself, which 

 shed short rivers, from 80 to 100 miles in length, eastward into Ross Sea, and large 

 rivers, like the Amazon and the La Plata, perhaps towards Kaiser William II. Land 

 and Weddell Sea respectively. 



An alternative is to suppose that previous to the late Cainozic glaciation of 

 the Antarctic the eastward flowing rivers of the Antarctic Horst had actually cut 

 through the horst and encroached on the sandstones of the down-faulted area of 

 the Beacon Sandstones in the neighbourhood of the present Ice Divide. This is 

 situated on the South Magnetic Pole plateau area, at about 200 miles inland, and 

 near Shackleton's Farthest South in lat. 88° 23' S. and long. 162° E., also a httle 

 over 200 miles inland from the coast-line of the Ross Barrier area. In either case 

 we are faced wltli the almost certain fact that there were a series of very short 

 rivers draining eastwards, with very long ones draining westwards and northwards. 

 If at the time immediately preceding the commencement of the Cainozoic glaciation 

 the main divide was still situated within the horst itself, we are forced to a very 

 interesting conclusion as regards the development of the modern transverse valleys, 

 now occupied by the outlet glaciers. It must be assumed that as the ice accumulated 

 on what had formerly been the western watershed of the horst, it gradually rose so 

 high that it was able to overflow the cols in the main divide, and so discharge into 

 Ross Sea as well as in the direction of Addlie Land, Kaiser Wilhehn II. Land, Enderby 

 Land, &c. Thus the di-ainage may have gradually been reversed by the ice of the 

 western jiortions of the outlet valleys becoming converted into obsequent streams. 

 This, of course, would not be the case if the Divide, previous to the coming on of 

 the Cainozoic glaciation, had already been driven back as far westward as 100 miles 

 west of the western side of the horst, the position of the present Ice Divide. Even 

 if it be conceded that many of the transverse valleys were originally partly tectonic 

 in character, partly of fluviatile origin, it must become apparent that their present 

 valley walls, so smooth, straight, and spurless, have been so extensively modified by 

 the sculpturing of glacier ice, by frost- weathering, and by fluvio-glacial action, that 

 all traces of former possible river action have now been eflaced. (See Plate LVIII. 

 of Chapter X.) 



Another view, which seems to be more probable, is that the formation of the 

 horst did not much ante-date, if at all, early Pliocene time. Previous to the faulting 

 mature valleys of fluviatile origin may have drained across the area where the horst 

 was about to rise. This is suggested by the oblique angle at which the Beardmore 

 Valley, the Barne Inlet Valley, &c., meet the trend line of the horst. This is 

 suggestive of a former radial drainage ante-dating the formation of the Ross Sea, 

 as, if the valleys entirely post-dated the formation of the horst and were purely 

 of glacial origin, the ice would probably have short-circuited to Ross Sea, producing 

 valleys at right angles to the trend of the horst. Then the Antarctic Horst became 

 developed, in a refrigerating climate. As a consequence the north-eastward flowing 



