316 E. C. ANDREWS. 



glacial valleys, and these in turn discharged into the more 

 youthful channels draining the upland surface. During the 

 waning of the ice sheet and the later phase of valley glaci- 

 ation the channel grades were readjusted and the huge 

 "steps" and "treads" of the earlier glaciation were cut 

 clown to make the present long straight-skied hanging and 

 main valleys of the Tilt System. 1 



Post-glacial stream action has formed narrow trenches 

 from 20 to 100 feet deep in these old ice modified surfaces. 



7. Kosciusko (New South Wales).— An examination of 

 the plateau of Mount Kosciusko throws much light on the 

 subject of glacial corrasion, because in this locality typical 

 cirques, hanging valleys, facetted spurs and rock basins 

 exist in the closest association with plateaus and profound 

 canons which have been developed by ordinary stream 

 action. Nowhere in the writer's experience is the close 

 association of two such types of topographic profiles so 

 impressive as on this plateau remnant. Even the mingling 

 of glaciated and non-glaciated topographies as seen along 

 the West Coast of New Zealand, and along the Merced 

 River below the famous Yosemite Valley in California, is 

 not nearly so instructive. A peneplain has here been 

 broken ; part of it has been hoisted above the snow line of 

 the recent Glacial Period, while the fault scarps, the deep 

 incising gorges, and tlie portions of the peneplain outside 

 of the Kosciusko areas remained below this snow line; the 

 Kosciusko plateau developed a crop of rock basins, hanging 

 valleys, facetted spurs and cirques, while the lower extra- 

 Kosciusko plateaus exhibit none of these features. The 

 suggestion that here two stream types worked side by 

 side is therefore almost undeniable. 



1 For a more detailed account of the Highland profiles and their origin 

 see Tarr (b). This is one of the clearest statements yet made as to the 

 peculiarities of glacial topography. 



