PKESIDENT*S ADDRESS. — SECTION C. 159 



That these high-level clays, sandstones,' and conglomerates have 

 an important place in the later geological history of South Australia 

 may be inferred from the following considerations-^(l) Their very 

 general distribution throughout the country, extending from the 

 south coast to the region of the inland lakes ; (2) their great thicknesses ; 

 (3) they have no relationship with the present river systems or lines of 

 drainage ; and (4) they occur at very different altitudes. It is evident 

 that they belong to a hydrographical system that has been entirely 

 wiped out, and the history of these dead rivers must be read in connexion 

 with earth movements that have entirely changed the face of nature 

 in the regions concerned. 



The dominant factor in the Neogene period of Australia is that 

 of 



A Great Uplift. 



We have already seen that the evidences point to the fact that, 

 io lower Cainozoic times, the Mount Lofty Ranges did not exist, but 

 that the land was, in the first instance, low and swampy ; then submerged 

 by the sea, during two successive periods ; and then, in post-Miocene 

 times was, in the main, permanently elevated into dry land. This 

 upward movement was continental in extent, and inaugurated a new 

 geographical cycle. 



South-central Australia has undergone but slight orogenic defor- 

 mation since early geological times. The orogenic energy that pro- 

 duced powerful foldings and overthrusts of the Cambrian sediments 

 died out in mid-Palaeozoic times, inasmuch as the Permo-carboni- 

 ferous glacial clays and sandstones are no more disturbed than the late 

 Cainozoics. In the Neogene uplift the movement was epeiro genetic — 

 a great regional plateau uplift, that extended far beyond the limits of 

 South Australian territory. This point has been established by the 

 important observations made by David, Andrews,* Hedley, Taylor, 

 and others, with respect to the eastern States, and demonstrates the 

 existence of a synchronal physiographic cycle, for post-Miocene times, 

 that includes a great part of the Australian continent. 



Within the South Australian region the elevatory forces gave a 

 gentle slope of the land from the north towards the south, with the 

 watersheds situated much further inland than is the case to-day ; the 

 sea retreated from the areas of the gulfs, and the shore line was pushed 

 further to the south. Had it been a simple, vertical uplift, this would 

 not have materially altered the drainage lines, except so far as the 

 rejuvenation of the streams and deepening of the gorges. This was 

 probably the state of things in the earlier stages of the uplift of the 

 South Australian peneplain, and led to the formation of the great 



* E. 0. Andrews, " Geographical Unity of Eastern Australia in Late and Post Tertiary 

 Tims." Jour. Roy. Soc. New South Wales, Vol. XLIV, pp. 420-480. 



