34 A FURTHEU NOTE ON THE TOPdGKAI'HV OK LAKK KENTON. 



the topography of the locality cannot be explained niei'ely as 

 an ordinary glacial valley blocked by a moraine. 



In investigating the occurrence of glacial remains 

 throughout the park, an observer cannot help being struck 

 with the regularity with which the lakes occur in pairs or 

 threes, one superimposed on another, at about an elevation 

 of 300 feet. Dr. Griffith Taylor gives the clue to the cause 

 of this phenomenon. (See particularly on this point Taylor 

 1921.) As he explains, the nivation layer or zone of maxi- 

 mum frost action has rested at one elevation for long enough 

 to erode cirques in the hillside. Later, this zone has moved 

 farther up the slope, where it has rested sufficiently long 

 to erode a second series of cirques out of the older ones, and 

 so on. 



This superimposing of cirques has occurred with re- 

 markable regularity throughout the area. In the Broad 

 River Valley there is a trace of an old cirque, which I had 

 not recognised previously, encircling the south-eastern, 

 southern, and south-western shores of Lake Webster. It 

 can be recognised by looking south from the outlet of this 

 lake, in the very steep bank over which the Fenton-Webster 

 track runs, and which runs west past the diabaso tlifTs men- 

 tioned at page 29 of my previous paper, including the bank 

 over which the water from Lake Seal flows, to the wall-like 

 side of Mt. Bridges, and farther north in the cliffs to the 

 north-west of Lake Webster. This cirque has now been 

 cut through and planed down near its centre, and vegeta- 

 tion has covered its slopes, but it was, apparently, in the 

 early stages of the Pleistocene Glacial Epoch, the seat of the 

 Broad River Glacier. 



Later the nivation layer lifted some 300 feet, and was 

 respon.sible for the erosion of the cirque at the head of the 

 Broad, the Lake Dobson, and the Lake Seal cirques, and the 

 cirque below Lake Newdegate. Here huge cirques were 

 hollowed out all at about the same level. 



Then the nivation layer rose 1,000 feet, and was re- 

 sponsible for the succession of small cirques in which the 

 Tarns now repose, and for the other glacial ledges mention- 

 ed by Dr. Taylor. Also it rested on Mt. Field East at a 

 similar level, eating into the plateau top until only a small 

 residual 150 feet in height, the present summit, was left. 

 The nivation layer then rose above these mountains. 



This succession is followed out in every detail through- 

 out in the field, as it is elsewhere in Tasmania, e.g., Cradle 

 Mountain, Mt. .Inlv-c--. Mt. Anne, and other glaciated plateaux. 



