Page:Native Tribes of South-East Australia.djvu/49

I of Tasmania, the soundings of 50,100, and 1000 fathoms are distant respectively about 5, 8, and 50 miles.

The lines of 50 and 100 fathoms soundings off the Murray mouth are distant therefrom about 100 miles, the two lines being apparently no more than 5 miles apart. At 100 miles, further south, there is a sounding of 2840 fathoms.

The general conclusions derivable from a study of these charts are that the 50-fathom line represents a submerged plateau connecting Victoria approximately from Cape Howe to Cape Otway with Tasmania. From it there is a more rapid slope to the 100-fathom line, and thence a still greater slope into ocean depths. An elevation of 300 feet would therefore lay dry a tract of comparatively level country between Victoria and Tasmania, rising to a central ridge on the eastern side. The plateau would be mainly not more than 100 to 200 feet above sea-level, but in places rising up to 3000 feet. On the western side a deep bend to the north-east indicates the former channel of a river conveying the combined waters of all streams and rivers which now debouch between Cape Otway and Wilson's Promontory, whose deposits probably account for the unusual distance between the 50 and 100 fathom line, from the embouchure down to Cape Sorrell.

The plateau of low-lying land thus indicated flanking the eastern side of the chain of denuded and eroded mountains, whose peaks are now islands in Bass Strait, would probably resemble the sandy and swampy country covered with dwarf scrub and coarse sedges which border Corner Inlet, and separate Wilson's Promontory from the Gippsland coast ranges.

A great delta is indicated by these soundings, extending between Kangaroo Island and Cape Jaffa, 100 miles beyond the present Murray mouth.

That the elevation and subsidence of the land has been by widespread and not merely local movements is shown by the Eocene and Miocene marine series of Victoria, South Australia, and Tasmania, which, although subjected to elevation, are in the whole, at low angles, little beyond horizontal.