CORRASION BY GRAVITY STREAMS. 319 



The faulted blocks were tilted towards the upper Snowy 

 River to the north and west of Jindabyne, and that stream 

 shows the influence of such action. Near its head in the 

 mountain summit it exhibits the repeated and characteristic 

 "valley in valley" structure common to the modified pene- 

 plain surface. Thence it starts on its torrent track as the 

 fault-block proper is traversed. 



Here then we have the singular conditions 1 which 

 obtained in the Kosciusko area during the recent ice periods. 

 In a word an area of a peneplain had been lifted to such a 

 height that the conditions became favourable to the develop- 

 ment upon it of glaciers during the recent Ice Age. By 

 faulting and stream action this area became an isolated 

 plateau less than 100,000 acres in extent. After the 

 isolation of Kosciusko by faulting and stream action an 

 ice cap formed on the plateau. (David, T. W. E., see 

 literature). As the glaciers crept over and along the old 

 wide and shallow upland valleys of the fault block, they 

 finally reached the precipitous faces which the block pre- 

 sented to the gorges of the Thredbo and the Murray. At 

 heights less than the general plateau level, however, the 

 conditions were unfavourable for the development of 

 glaciers. On the southern side therefore the ice simply fell 

 in great masses down the unbroken escarpment overlooking 

 the Thredbo River. On the western and northern aspects 

 the Murray receives the drainage of its extremely short 

 hanging valleys, and because the side streams here had 

 excavated narrow although precipitous channel grades to the 

 main stream, the ice cap in this quadrant sent out thin 

 tongues towards the Murray base. These however were 



1 Certain fault blocks in California visited by the writer in company 

 with Dr. G. K. Gilbert and W. D. Johnson show an association of glaciated 

 and non-glaciated topography similar to that of Kosciusko, but their 

 appearance is not so impressive as that of Kosciusko, owing to the great 

 amount of unreduced plateau in the latter locality. 



