PRE-GLACIAL HISTORY OF SOUTH VICTORIA LAND 291 



PART II. PROBABLE PRE-GLACIAL HISTORY OF SOUTH 

 VICTORIA LAND IN CAINOZOIC TIME 



The important question naturally suggests itself, if the whole of the ice and snow 

 were cleared off from the surface of the Antarctic continent, what would be the 

 nature of its present physiography ? And next, what was the probable physio- 

 graphic relief of the land in early Miocene time when, as the evidence collected 

 by Dr. Otto Nordenskjold's Expedition suggests, the whole continent was probably 

 ice-free ? 



Before any guess may be made at the answer, the further question has to be 

 considered as to when did the main faulting take place which produced the great 

 Antarctic Horst. In the absence of direct stratigraphical evidence, further than 

 that the faulting is Post-Beacon Sandstone, that is, most probably Post-Gondwana, 

 probably Post-Cretaceous, we have to rely chiefly on the amount of dissection which 

 the horst has undergone subsequent to the epoch of faulting. Some important 

 conclusions follow from the considerations of the probable answers to the above 

 questions. The great depth to which the transverse valleys of the great horst have 

 been excavated, such excavation probably for the most part subsequent to the 

 faulting, suggests that the faulting has taken place at some epoch ante-dating the 

 Post-Pliocene. It has been shown that in the Auvergne valleys have been excavated 

 to a dejith of about 1500 feet (457 metres) since late Pliocene time; but the 

 transverse valleys of the horst, like the Beardmore Glacier Valley, have been eroded 

 to a depth of fully 6000 feet (1828 metres). Perhaps more than Post-Pliocene time 

 is needed for such a vast amount of erosion. 



If, as Mr. Allan Thomson, in this Memoir, supposes, the widespread injection 

 of quartz-dolerites, in the Southern Hemisphere, was connected with the breaking in 

 and foundering of large areas of Gondwana Land, then the major part of the faulting 

 which produced the Antarctic Horst may be ascribed to some late epoch in the 

 Cretaceous Period, for the evidence in Tasmania and South Africa shows that these 

 quartz-dolerites, while they strongly intrude the Trias-Jura rocks, are themselves 

 capped by later deposits, prol^ably of Eocene age. In South Africa, according to 

 Rogers, the date of their injection lies between Upper Jurassic and Upper Cretaceous. 

 It may, therefore, be provisionally assumed that the principal tectonic movements 

 which gave rise to the Antarctic Horst date for their beginnings to about the com- 

 mencement of the Cainozoic Era. The existence of this long, comparatively narrow, 

 elevated strip of the horst would probably give rise to a system of drainage much like 

 that of the northern part of South America. It is doubtful whether, even in the long 

 time that has elapsed since the Cretaceous, the rivers draining into the Ross Sea, and 

 that southei^n part of it now occupied by the Ross Barrier, would have had time to cut 

 back their valleys completely through the great horst so as to encroach on the 

 region of westerly drainage on the other side. It is possible that, previous to the 



