Promontory and Kent Group. It is shallower between that island and Flinders Island, and still shallower thence to Cape Portland.
A 35-fathom line on either side would indicate a plateau 80 or 90 miles wide connecting the shores of the strait, and on the Victoria side widening out so as to extend up to Cape Howe.
On this there would be a low ridge from Wilson's Promontory to Cape Portland, with occasional elevations—now islands—rising at Mount Strzelecki to over 2700 feet above the sea. These islands are, therefore, a submerged continuation of that part of the Cordillera which ends in Victoria at Wilson's Promontory. The prevailing rocks, except a few isolated peaks of recent igneous origin, are granite and schists, which on the low-lying tracts are overlaid by deposits of Eocene age covered by recent formations.
These islands are, therefore, composed of Palaeozoic plutonic rocks and metamorphic schists similar to those largely represented in the Gippsland Mountains, which terminate in a southerly direction in Wilson's Promontory.
An inspection of the soundings shows that the 50-fathom line encloses a comparatively level plateau, which falls more rapidly and in places almost suddenly, to the 100-fathom line, especially on the western and southern side of Tasmania. Beyond this there are few soundings, but from those given the following statements may be noted.
The 50-fathom line is distant about 40 miles in a south-westerly direction from Cape Otway; at 10 miles further off is the loo-fathom line; at 20 miles further the depth is over 900 fathoms; finally, at 150 miles from Cape Otway, in the same direction, there is a sounding of over 2300 fathoms.
Similarly, in a south-easterly direction from the Ninety-mile Beach in Gippsland, the 50-fathom and 1OO-fathom lines are distant 50 and 70 miles respectively.
South-easterly from Cape Pillar, in the extreme south
- Johnston, Robt. M., Systematic Account of Geology of Tasmania, p. 365, Hobart, 1888.