president's address. — SECTION C." 167 



This movement of depression in the north, which at its deepest 

 point passed below sea-level, had the effect of creating a broad corru- 

 gation, or swelling of the surface, between the sunken area and the sea. 

 In this way an irregular east and west water-parting was established, 

 forming the southern lip or barrier to the central basin. The effect 

 was to behead all the north and south river systems, the greater part 

 of the drainage was reversed, and being directed inwards formed a 

 countless number of shallow lakes. (Plate III.) 



On the western side, the Gawler Range's formed the barrier which 

 threw back the drainage that now gathers in Lakes Gairdner, Everard, 

 Roundabout, and maiiy others. The peneplain around Petersburg, 

 Belalie, and Orroroo became a water-parting, 25 miles wide, that inter- 

 cepted the rivers that formerly emptied themselves into the head of 

 Gulf St. Vincent, and, by the reversal of the drainage at that point, 

 led to the formation of Lakes Frome, Callabonna, Gregory, and others 

 of the north-east region. Lake Torrens and Lake Eyre retain the waters 

 of Central Australia, which formerly found their way to the head of 

 Spencer Gulf. Lake Torrens, lying in the rift valley, still maintains 

 an imperfect connexion with the sea by an almost continuous chain 

 of shallow lakes and clay-pans. 



The relation of the River Murray to these important earth move- 

 ments is a subject of special interest. A slight glance at the map is 

 sufficien.t to show that the Murray is a great river system of marked 

 asymmetry. Its radial structure is not simply imperfect, it is con- 

 spicuously lop-sided. The Murray is a continental river, but while 

 having its outlet on the south coast it gathers its waters almost exclu- 

 sively from the east. A vast country to the north and north-west 

 properly belongs to its former hydrographical province. The River 

 Murray has suffered a great amputation ; the whole of its former north- 

 western drainage has been severed from the trunk and dismembered, for 

 where a symmetrical system of reticulating streams should exist there is 

 nothing but hundreds of fragments, which are erratic in their course 

 and intermittent in their flow. 



The north-eastern drainage of South Australia, under the former 

 hydrographic system, was directed partly to the River Murray and 

 partly to the heads of the Gulfs. The whole of that north-eastern 

 country is deeply covered with fluviatile material. The main valleys 

 are wide and choked with alluvium, above which steep-faced hills 

 rise in widely-separated and isolated patches. 



Evidences point to the fact that the subsidence of the inland basin 

 was gradual and prolonged. During the period when the sagging 

 slowly reduced the grade and the land approached to a condition of 

 base-level, the rivers became less and less capable of carrying their 

 load, every channel was being blocked, billabongs and backwaters 

 formed lakes, until the increasing northerly tilt closed the way to the 



