president's address. — SECTION c. 151 



tte intervening plateau, and the sediments, whicli must have been 

 relatively thin, since removed by denudation ; or the older rocks of 

 Western Australia and South Australia may have formed a land-barrier 

 to the imion of the two branches or gulfs of the cretaceous sea, the one 

 coming in from the north and the other from the south. In any case, 

 the discovery is one of first importance, and must be taken into account 

 in .explaining the physiographical development of the Australian 

 Continent. It demonstrates that there was no extension of the conti- 

 nent in that direction during cretaceous times. 



We now come back to the South Australian evidences. The geo- 

 logical data, so far as they are at our command, are strongly indicative 

 of sub-aerial conditions in the time immediately preceding, or as initia- 

 tive to the Cainozoic period of southern Australia. We have already 

 inferred the existence of highlands to the south of the present coast- 

 line of South Australia, dating from early ages to the cretaceous. The 

 loss of these southern watersheds and the tilting, to the south, of the 

 southern portions of the continent, resulted in much of the land sinking 

 below sea-level, and marks a critical period in the evolution of existing 

 land forms. It created a new geographical axis in the country, situated 

 further to the north than previously, and had the effect of reversing 

 the drainage which, from that time, no longer flowed northwards, but 

 was directed to the south, from which direction the sea had advanced. 



The disappearance of the southern watershed must have resulted 

 in important cUmatic changes. The existence of land to the south 

 would place the continent in a more favorable position for receiving 

 a more generous rainfall — such as now occurs on the western side of 

 Tasmania. A watershed in this position (if not so high as to establish 

 a barrier to the rain-beaiing winds), would supply perennial streams 

 that, flowing northwards, would carry fertilizing waters far into the 

 warmer latitudes. The physiographical changes that occurred at the 

 close of the Mesozoic Age, carrying with them the loss of the south-to- 

 north system of drainage, probably marks the first stages in that process 

 of desiccation which, accentuated by later earth movements, has led 

 np to the arid and sub-arid conditions of the present day. 



LOWER CAINOZOIC (EOCENE).* 



Freshwater ^mes.-The lowest members of the Cainozoic series, 

 in South Australia, consist of freshwater muds, sands, grits, fine gravels, 

 and carbonaceous deposits. These beds, which vary in thickness up 

 to 500 feet or 600 feet, have been proved in almost all the bores that 



* It Is probable that the chronology of the Cainozoics of southern Australia, as adopted by 

 the late Prof. R. Tate and Mr. Dennant, may have to be modifled, in view of recent discoveries. 



