BY A. N. LEWIS, M.C. 1 



Time has not allowed a detailed examination of the 

 sedimentary rocks of the Park. Near the entrance, and ex- 

 tending for some distance up the Tyenna Valley, are beds 

 of Permo-Carboniferous lime — and mud — stones. These are 

 overlaid by over a thousand feet of sandstone in huge, com- 

 pact beds, in which strata can be scarcely distinguished. 

 From general observations, all these sandstones appear to 

 be of the Trias-Jura age, similar to the Knocklofty series so 

 well known in Southern Tasmania. These beds have been 

 distinguished by Mr. Loftus Hills at the foot of Mt. Field 

 West in the Florentine, but their age requires confirma- 

 tion elsewhere. 



The drainage is typical of the stage known as juvenile, 

 and most of the streams are mere mountain torrents. Dur- 

 ing the Pleistocene times, the cycle of river erosion was in- 

 terrupted by glaciers in the higher altitudes. These have 

 widened many of the valleys and dammed them in places, 

 forming lakes and causing the streams to meander over an 

 almost level bed. The Upper Broad River has the appear- 

 ance of being in the mature stage, but it is really cutting 

 through a valley not of its own making, and from which 

 it has not yet had time to remove the remains of the 

 glacier. In a day's walk along this valley, the student can 

 see every form of river erosion. 



The glaciers which caused this, and the way they have 

 moulded the topography of the plateau, it is now the main 

 purpose of this paper to describe. 



THE COURSE OF THE PLEISTOCENE GLACIERS. 



At the same time as the western half of Tasmania 

 was more or less under ice, and from the same cause, snow- 

 fields accumulated on the Mt. Field Plateau, and glaciers 

 flowed a little way down the valleys. It is well known that 

 the Pleistocene Ice Age was not of uniform coldness. Dur- 

 ing periods of milder climate the glaciers shrank towards the 

 mountain tops, and in intervals of intense cold they pushed 

 out down the valleys. Unfortunately, a glacier tends to 

 erase all traces of earlier action by its latest flow, but still 

 we can see to what point the glacier reached, and trace the 

 stages of its final retreat. 



During the period of maximum glaciation, a permanent 

 snow cap covered the entire top of the Mt. Field Plateau, and 



