HY A. X. LEWIS, M.C., LL.B. 35 



(c) Cycle of Glacial Erosion in Tasmania. 



There is one further phase of the study of the Pleisto- 

 cene glaciation in Tasmania that deserves passing mention. 

 As in the case of water-eroded topography, we have in glacial 

 topography a cycle of erosion corresponding to the length 

 of time during which a locality has been subjected to the 

 effects of ice. Professor Hobbs defines the possible classes 

 as follows: — 



(1) The youthful channelled or grooved upland. 



(2) The adolescent early fretted upland. 



(3) The fretted upland of full maturity. 



(4) The monumented upland of old age. 



In the case of (1), cirques and glacial valleys merely groove 

 the upland, leaving much of the pre-glacial surface still exist- 

 ing and clearly recognisable. In (2) the cirques have 

 extended until they have met, and are separated by a ser- 

 rated "Comb" ridge representing all that is left of the 

 original surface. In (3) these lateral combs have disap- 

 peared leaving glacial horns (e.g., the Matterhorn) standing 

 at the place where the heads of the cirques of the district 

 junction. In (4) even this has disappeared, and all that is 

 left are pairs of twin peaks, or "monuments," which formed 

 that part of the upland which stood at the entrance to the U 

 valleys, these be-ng the last to be affected by the cirque 

 enlargement, which takes place from the head outwards 

 (Hobbs, 1910, 1921). 



In Tasmania most of our glaciated areas have reached 

 H stage bordering on the adolescent, early fretted upland. 

 In most areas there is very little pre-glRcial_ upland left. In 

 the case of the National Park there are stretches of pre- 

 glacial surface a few hundreds of yards across on the Field 

 West and Mt. Mawson ridges and a mile or so on the Field East 

 ridge, where the glaciation has not been so severe, while the 

 Hayes and Newdigate Cirques have eaten into the Rodway 

 ridge until the pre-glacial surface has disappeared, and we 

 see the beginning of the formation of a comb ridge. 



On La Perouse there is a very fine example of a comb 

 ridge. On the Mt. Anne range the process has extended a 

 little farther. The cirques have commenced to cut down the 

 comb ridges between them, and we see rudimentary glacial 

 horns appearing in "Lot's Wife," the cone-shaped pinnacle 

 to the east of Lake Judd, and the summit of Mt. Anne itself. 

 On Cradle Mountain the process has gone .still farther until 

 the separating ridges have been quite smoothed out and the 



