58 



ance, now that the trees have been removed, is not very 

 suggestive of the name, whatever it, once, may have been. 

 Its cone, rising from the centre of the lake, and composed 

 for the most part of unconsolidated tuff would soon yield to 

 that greatest of all levellers — water — and this may account 

 for its present tame and rounded appearance. 



Probable Extent of the Lake Basin. 



Taking into consideration the existing levels of the plains and 

 valleys, whose water-shed is received by the Tamar, and bearing 

 in mind the great altitude of the highest beds of the system, 

 the waters of this old lake must have covered not less than 

 600 square miles of what now is the most fertile and cultivated 

 portion of the island of Tasmania. It is also evident that had 

 it not been for the distribution by the waters of the lake of the 

 ejecta of the more receut volcanic eruption, that those plains 

 which are now so fertile, would be most sterile and unproduc- 

 tive. 



In support of the opinion that the waters of the lake 

 extended along the great valleys and plains in the direction of 

 Fingal, Ross, Westward Plains, and the Tamar Valley, I may 

 state the following observations. 



Stratified beds of the system are found at least 500 feet 

 above the existing beds of the water courses. 



In a shaft sunk to a depth of 40 feet, by Mr. Grant, of 

 Tullochgorum, near to his house, he passed through arenacious 

 clays containing lignites identical with those of Breadalbane. 

 Fossil leaves are also found closely resembling those found at 

 Muddy Creek. The same whitish arenacious clays and sands 

 were found to nearly a depth of 100 feet, in a well sunk by 

 Mr. Fincham near to Cleveland. It is evident, therefore, that 

 the extent is not over-estimated, and that there must have 

 been a very slight separation between the borders of the lake 

 and the Derwent Valley. 



Denudation. 



Another remarkable feature is the amount of denundation 

 of the system that appears to have taken place. Throughout 

 the whole basiu, but more especially in the Launceston and 

 Breadalbane districts, the waste in scooping out the existing 

 vallevs must have been immense. The level of the swamp at 

 Launceston is at least 500 feet below the stratified drift of the 

 same system in its immediate neighbourhood, and it is no 

 exaggeration to say that 15 to 20 miles of strata 400 to 500 

 feet thick, have been swept away from the immediate vicinity 

 of Launceston alone. 



