28 GLACIAL REMAINS IN THK NATIONAL PARK, 



the author saw two stones measuring 6 feet by 2 feet stick- 

 ing on their ends out of the ground at different angles, and 

 balanced across them lay a flat boulder, with a diameter 

 of about 6 feet and a thickness of 1 foot. These deposits 

 descend to the shore of Lake Seal, 200 feet below, and it 

 is impossible to tell the depth of the deposit on this side, 

 but on the edge of the Broad River Valley they soon dis- 

 appear. They extend westward beyond Platypus Tarn, 

 which lies in a hollow in this till. 



From the centre of this ridge the morainal deposits 

 curve round the top of the steep gully immediately to the 

 south, and run past Eagle Tarn to the eastern shore of 

 Lake Dobson. They appear to keep the same level at which 

 we saw them on the ridge, not stretching far down the gully, 

 and they do not extend far up the slopes of Mt. Mawson. 



At the western end of Lake Seal there can be seen a 

 most perfect specimen of the glacial phenomenon known as 

 a cirque. The glacier has eaten the foot of the hill away 

 until the lake now ends in a wall 1,000 feet high, consist- 

 ing of a series of rugged cliffs. The glacier has cut farther 

 in to the north-west corner, and here formed a smaller 

 cirque within the greater feature, making, indeed, a nail- 

 shaped valley, a common feature in glaciated country. 



The ice fed by the snow on the ridge above the tarns 

 flowed in a sheet down the slope until it hit the ridge on 

 which the tarns are now to be seen, which appears to run 

 right round the eastern face of Mt. Mawson, a common 

 feature on diabase mountains. Here its pace was check- 

 ed, but it pushed on, until divided by the shoulder of Mt. 

 Bridges, one half dropped over into the Lake Seal cirque, 

 and the other into the cirque at the head of the valley 

 leading to Lake Webster. 



Where it hit the ledge of rock in its descent it ground 

 great basins out of the solid rock, and it polished and 

 rounded the outer portion of the ledge. In these rock basins 

 water has accumulated which we now know as the six 

 tarns, and between them and the edge of the two cirques 

 — only a matter of fifty yards in the case of Robert Tarn — 

 the diabase has been rounded and smoothed into waves 

 of roches moutonnees, very distinct towards the southern 

 end of the line of tarns. Many huge erratics stand on these 

 and lie scattered over the; country side, and towards Lake 

 Newdegate there are considerable deposits of mcrainal 

 material. 



