Ixi. 



There is much reason for the belief that the " Desert Sand- 

 stone " is an extensive lacustrine deposit ; coeval with the 

 accumulation of the river gravels and sand of the hilly country- 

 classed by me as Upland Miocene. 



Summary. — The marine Older Tertiaries, which belong to the 

 Eocene and Miocene epochs, are confined to the existing coast- 

 line, and extend inwards from thence in gulf and bay-like 

 projections. They do not attain an elevation much above 250 

 feet. Beyond these are the vast sterile tracts of the interior of 

 the continent occupied by the lacustrine formation termed the 

 " Desert Sandstone," which is contemporaneous with the 

 youngest member of the Miocene marine strata. At various 

 places in South Australia, Victoria, and New South "Wales 

 plant-deposits occur among silicified sandstones and quartzites, 

 often at great elevations and in several instances associated 

 with the goldfields underlying the basalts. 



Some excuse may be tendered on behalf of those, who, 

 having no other source of information than that contained in 

 Brough Smyth's geological map of Australia, have indulged in 

 representing this continent during Miocene times as being for 

 the most part submerged beneath the ocean. These Tertiary 

 deposits were not subjected to any other alterations in their 

 relative level than those of the most local kind. The elevation 

 of the southern shores of the continent at the close of the 

 Miocene period was equable, and measured by the vertical 

 thickness of the deposits and heights at which its littoral 

 margins now exist, it could not be more than about 150 to 200 

 feet within the Aldinga and Murray Basin. A depression to 

 this amount would not submerge the interior of the continent, 

 and would be too small to materially affect the rainfall, so that 

 the vast rivers which now drain the Cordilleras must have 

 then, as now, flowed in the same direction, but have discharged 

 their waters into the great central basin — bounded on the 

 north by the Highlands of New Guinea, on the east by the 

 Great Dividing Range, extending on the south to the Grampians 

 of Western Victoria. This. vast inland lake or estuary was 

 dotted with islands now forming the elevated parts of the 

 Minders and Adelaide Ranges, and other mountain masses in 

 Central Australia, each with its own river basins in which were 

 accumulated the fluviatile gravels which are scattered at various 

 heights among our hills. 



The denudation of the Desert sandstone since it became dry 

 land has been excessive, and that of the marine deposits has 

 been very great, as is fully attested by the existence of the 

 wide guli' of St. Vincent's which is excavated out of them, and 

 by the precipitous front of the Bunda cliffs and their 

 ascertained extension below sea level for a distance of several 

 miles. 



