THE AUSTEALIAN SEAS AND ISLANDS. 



363 



by a general upheaval of less than twenty-five fathoms, and Tasmania, which was 

 long supposed to form part of the neighbouring continent, really belongs to it 

 from the geological point of view. The presence of glaciers probably contributed 

 to preserve the primitive form of the Tasmanian seaboard, all the south side of 

 Avhich is carved into creeks and inlets, evidently ancient fjords which have main- 

 tained their original depth and outlines. 



A close resemblance to the sea which formerly flooded South Australia, is pre- 

 sented by the channel at present separating this continent from New Guinea. 

 Between Cape York and Mount Cornwallis at the narrowest j)art of Torres Strait 



Fig. 1.56. — Bass Steait. 

 - Scale 1 : 5,555,000. 



Lfibb :F Greenwich 



Depths. 



to 10 

 Fathoms. 



10 to 25 

 Fathoms. 



25 to 100 

 Fathoms. 



100 Fathoms 

 and upwards. 



120 Miles. 



the water is nowhere more than eleven or twelve, while the average scarcely 

 exceeds seven fathoms. It was shown by the accurate surveys of the Fly and 

 Bramble (1842 — 1847) that, even by keeping to the windings of the deepest 

 channel, a vessel drawing over 30 feet could only pass through in perfectly 

 smooth water. The rocky islets in this strait, whether isolated or grouped in 

 clusters, consist exclusively of porphyries or syenites, like the rocks in the northern 

 peninsula of Queensland, of which they evidently form a seaward extension. 



East of these reef-fringed islets, between which flow channels perfectly free 



