662 GEOLOGICAL NOTES ON KOSCIUSKO, 



year after year for thousands of years at a particular spot, the 

 drifts perhaps disappearing only for a few weeks in each year* 

 may preserve very effectively a small surface of granite rock, 

 glaciated it may be 50,000 years ago, while in the immediate 

 vicinity former glaciated rock-surfaces, not so protected by snow- 

 drift, may become considerably weathered so as to prod ace the 

 tor structure already referred to. It is obvious that the strongly 

 marked differential weathering one sees so frequently on the 

 Kosciusko Plateau is to be correlated chiefly with differential 

 thickness of snow-covering. Obviously, too, variations in thickness 

 of once protecting covering of morainic material has also played 

 an important part, though not so important it seems as the snow 

 drifting, in protecting old glaciated surfaces from the destructive 

 action of the weather. 



In the second place, in my original observations I had vastly 

 underrated the age of the glaciation. The maximum glaciation, 

 for reasons which will be adduced presently, probably took place 

 at a period of time removed from 100,000 to 200,000 years from 

 the present. 



It may be stated at once that while evidences such as those 

 grouped under (2), (3), (4) and (5) are most conspicuous in con- 

 nection with the latest phenomena of Pleistocene glacial action 

 at Kosciusko, the phenomena of U-shaped valleys, hanging valleys, 

 filled-up lake-basins, and smoothed rock-surfaces are now the chief 

 evidences to be relied upon for the former extent of the maximum 

 glaciation. 



Of the kinds of glacial evidences which are preserved amongst 

 recent glacial phenomena, special reference may be made to the 

 beautiful glacial lake known as the Blue Lake. On the evidence 

 of this lake, and the extensive moraines below, between Hedley 

 Tarn and the valley of the Snowy, in Evidence Valley, it was 

 asserted in our previous paper that the glaciers came down to 

 within 5,800 feet of sea-level from the summit of Kosciusko, 

 which according to the most recently reduced trignometrical 

 observations is about 5,305 feet above sea-level. We are now, 

 however, in a position to state that the ice came down probably 



