318 E. C. ANDREWS. 



cally streamless. The youthful gorge in which the captured 

 Thredbo now flows is about 3,000 feet deep. 



In passing it may be mentioned that the peneplain itself 

 had been dissected to the old age stage before it had been 

 raised, and furthermore that the upland valley system had 

 been in turn trenched by broad mature and shallow "valley 

 in valley" structures. 



As the Thredbo cut its way back through the faulted 

 mountain block, it marched clean across the directions of 

 the streams draining the well matured valleys of the 

 plateau. Thus to one standing on an old flat-floored valley 

 draining the faulted block and looking upstream, the floor 

 apparently ends suddenly in space. On walking up this 

 flat floor one suddenly comes to a sudden break in the 

 country, and looks down a uniform and precipitous slope 

 exceeding 3,000 feet in depth to the present Thredbo gorge. 

 To the front of the observer the whole country apparently 

 has been dropped to a much lower level. Looking along 

 the gorge from a high vantage point on its edge, the ravine 

 appears to run as a fairly straight line which truncates 

 other mature valley floors and walls of the faulted block in 

 its passage. Scarcely any drainage goes from these old 

 valleys into the Thredbo because the fault block slopes 

 away from the latter valley and the great gorge cuts across 

 the old valley floors clean as a knife to the limit of vision. 



The Murray gorges are much deeper than those of the 

 Thredbo, and have developed valleys possibly 4,000 feet in 

 depth on the western side of the block. The old well- 

 matured western valleys of the peneplain have by this 

 action been hung up for thousands of feet above the 

 present Murray waters. These, possibly, are some of the 

 finest examples of hanging valleys known to science which 

 have been developed by the methods of ordinary stream 

 revival. 



