GEOLOGY OF KING ISLAND, BASS STBAITS. o63 



out V-shaped valleys, and the south-eastern corner of the 

 island is a maze of small but steep hills and valleys. The 

 southern half, then, of the island is typically a diss.-rtrd 

 plateau of a youthful type. That the northern half is not 

 so is to be explained by its excessively low relief and its 

 continuous fringe of sand-dunes rather than by a separation 

 in age of elevation. On the western side the presence of 

 the fringe of high sand dunes has an important influence on 

 the drainage and consequent denudation of the island. The 

 dune area is considerably higher than the adjoining inland 

 country. The drainage is therefore temporarily stopped at 

 the junction, and this gives rise to numerous bogs, marshes 

 and shallow lagoons which are relieved by slow soakage 

 through the dune sand to the coast. The larger streams 

 have been able to keep open an outlet which, as in the case 

 of the Ettrick River, takes the form of a gorge bordered 

 on both sides by dunes up to 250 feet in height. This stag- 

 nation and the general low relief have combined to cause 

 a feature which is highly characteristic of the island. 



Except in the few localities where outcrops of rock are 

 found, the surface of the island is covered to a depth of 

 several feet with a loose sandy soil, which in the low lying 

 areas is replaced by peat. The sand is not worn to any 

 appreciable extent, and is formed of grains of quartz and 

 felspar, and is everywhere mixed with much decayed 

 organic matter. The presence of angular fragments of the 

 slates and quartzites, scattered through the soil and sub- 

 soil, confirms the idea that it is merely the disintegrated 

 original rock and is not transported detritus. Occasional 

 patches of yellowish stiffer soils seem to mark the position 

 of dyke rocks, as was definitely proved in one case. It is, 

 therefore, only along the coast that extensive outcrops of 

 rocks occur. 



A study of the submarine contour lines in the western 

 part of Bass Straits shows that the gradient is decidedly 



