BY PROFESSOR GRIFFITH TAYLOR, D.SC, B.E., B.A., F.G.S. 191 



erosion; but how much erosion by ordinary streams preceded 

 the advent of the Ice Age? And further, was the glacial 

 erosion due to glacier planation (i.e., by the rasping and 

 plucking due to debris cemented on the sole of the glacier) 

 or to the method which has been termed "nivation"! 



Evidence as to the great amount of erosion accomplished 

 since the last period of uplift is obvious throughout Tas- 

 mania. The gorge of the Ouse is cut down 1,200 feet, while 

 the King River canyon is even more striking. A better- 

 known example lies in the suburbs of Launceston, and offers 

 a wonderful study to the Tasmanian geographer. Here the 

 South Esk enters the Tamar estuary through a most pic- 

 turesque notch giving the clearest evidence of late uplift; 

 though later subsidence (3) has drowned the mouth of the 

 gorge. Probably Corra Lynn gorge and the Punchbowl, a few 

 miles to the south-east, are due to the same differential 

 movement between the Tamar estuary and the environs of 

 Launceston. The positions of these most interesting exam- 

 ples appear on Figure 1. 



We may therefore, I think, postulate a considerable 

 amount of erosion in the pre-glacial period, giving rise to 

 valleys, perhaps 500 feet deep, where now flow the Broad 

 River and the creeks draining north and south from K Col, 

 through Lake Hayes and Lake Belcher. These pre-glacial 

 valleys would be of a juvenile type with V cross sections, 

 and the thalweg would fall rapidly in the first mile of each 

 stream. (See Fig. 3.) 



Fig. 3. — Block diagram illustrating approximately the pre-glacial 

 drainage of the Plateau. 



It will be seen, therefore, that the striking cirque valleys 

 of Lake Hayes, Lake Belcher, and Lake Seal were originally 



(3) Daly would explain this drowning as due to the melting of the 

 world's ice caps after the Ice Age. 



