36 NOTES ON THE GEOLOGY OF CRADLE MOUNTAIN DISTKICT, 



basin of Lake Will, at the foot of the Bluff. North-east 

 of the Bluff the ice-sheet moved across the plateau and 

 fall into the gorge of the Forth River. Numerous smaJl 

 lakes were developed, such as Windermere and Agneiw,, 

 their position probably depending on differential erosion, 

 the mica-schists, and the soft Permo-carboniferous sedi- 

 ments being easily picked out. The ridge running to 

 the south-east from the Bluff separated the northerly from 

 the southerly flow, and is heavily cumbered with morainic 

 material. Plucking of blocks of rock out of their original 

 position must have gone on to a great extent, for one finda 

 large blocks (up to 16 by 11 feet in area.) of comparatively- 

 fragile coal measures, Iving among the debris (Montgomery 

 13). 



The eastern side of the ridge joining Barn Bluff and 

 Cradle Mt. is broken into a great cirque with minor embay- 

 ments, which surround the heads of tributaries of the 

 Forth Kiver. The ridge consists of horizontal sediments 

 lying on the ancient rocks, which form the floor of the 

 broad and relatively shallow cirque. Its eastern side 

 has been sapped back into a continuous cliff. The floor i^ 

 heavily glaciated and littered with morainic material. To 

 the east the glacier from this cirque joined the ice-sheet on 

 the plateau and fell over into the Forth River Gorge. 

 W^est of the connecting ridge there is little sign of glacia- 

 tion, the surface sloping regularly down into the Fury 

 Gorge. Possibly the dominant west wind prevented the 

 accumulation of much snow on this slope. (^^) 



East of Cradle Mt. is the grandest example of a 

 cirque m the district. On its floor is the lake for 



which the name Lake Rodway has been suggested. It 

 lies in a broad and deep trough, around the head of which 

 rises the crescentic ridge of Ci-adle Mountain. It is 

 probable that the name of the mountain was derived from 

 the resemblance this trough and rim-ridge bear to a miner's 

 cradle. The crescentic form of the ridge is due to the 

 cirque eating deeply into the eastern side of the original 

 monadnock, while the western side has been scarcely 

 affected ; a further instance of asymmetry. The cirque is 

 T,ot simple, but is broken into four steps, by transverse 

 bars of quartzite. (See Plate 3.) The ''treads" of the two 

 upper steps are narrow, the third is broader, and bears 

 a small shallow lake, the outlet of which falls over a 

 stronglv glaciated bar into the main basin of Lake Rod- 

 way, the depth of which has not been ascertained. A 



(14) Compare G. K. Gilbort. Sv=tpmAtic A symmetry In the High Sierras 

 of CaliforBia. Journal of Geol., 1904, pp. 570-586. 



