CORRASION BY GRAVITY STREAMS. 317 



It will be advisable to devote an introductory paragraph 

 or two to the general physiographic features of Kosciusko, 

 so as to throw as much light as possible on the subject of 

 ice corrasion. 



The strong glaciation of the Kosciusko Plateau in recent 

 times has been definitely proved by Professor David, Mr. 

 E. F. Pittman, and Mr. R. Helms. As a result of their 

 work 1 two glacial periods at least are known for the plateau, 

 an earlier one during which the locality was covered by an 

 ice cap and a later one during which the glaciers were of 

 the valley type. 



General Physiography, — The Kosciusko plateau is an 

 isolated block of the great peneplain of eastern Australia. 

 In the neighbourhood of the Great Divide of the eastern con- 

 tinent, the general height of this now raised peneplain is 

 about 3,000 feet, but in north-eastern Victoria and at 

 Kosciusko (in south-eastern New South Wales) it has been 

 strongly flexed and carried to heights varying from 5,000 to 

 7,300 feet above sea-level. At Kosciusko itself the flexing 

 has been most pronounced and relief found by faulting- 

 The great fault 2 which separated Kosciusko from theMonaro 

 peneplain which latter is about 3,000 feet less in altitude, 

 was not accomplished by one, but by several steps. The 

 directions of the Snowy and its strong tributary the Thredbo 

 River, were altered by the faulting, and near the junction 

 of the two rivers a stream commenced to work its way 

 back along the line of the fault, and thus developed a pro- 

 found Y-shaped gorge, about 30 miles in length, partly 

 along the fault line and partly beyond it. In working along 

 the line of weakness it captured the Thredbo, and so left 

 the broad matured valley of that strong tributary practi- 



1 David, T. W. E., Pittman, E. F. and Helms, E., see literature. 

 8 David, T. W. E„ pp. 659, 660- 



