AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 45 



a time interval between the scoria-cone phase in the Camperdown 

 district and the lava-plains, is evident from the fact that while no 

 scoria-cone flow shows sign of fluviatile dissection, the stream- 

 system on the lava-plains is mature. 



Earlier accumulations of the Hampden Tuffs, a tuff-series so- 

 named by Grayson and Mahony, cover extensive areas near 

 Camperdown and Lake Keilambete as well as the floors of Lake 

 Bookar and Lake Terang. Since it covers the floors of these and 

 other lakes and swamps, their basins were formed either during 

 or before its accumulation. Its earlier phases are distinct from 

 the scoria and sc< >ria-cone lava-flows which in places rest on it, 

 while it in turn rests on the mature topography of the lava-plains. 

 The time taken for the lava-plains physiographical cycle to reach 

 maturity is the interval between the accumulation of these earlier 

 phases of the Hampden Tuffs and the extrusion of the lava- 

 plains. 



That the final accumulations of the Hampden Tuffs are quite 

 recent, is shown by their position in the Pejark Marsh section 

 (Fig. 5) where the series is covered by only 3 feet of soil; there it 

 is only 2 feet thick and the attenuated edge of a thick series of 

 tuffs on the slopes of Mt. Terang (c/. Walcott, 1919), it rests on 

 black clay which rests on yellow clay that also contains volcanic 

 ejectamenta. The texture of this yellow clay suggests that it was 

 deposited during the the arid period of The Postglacial Optimum, 

 and the black carbonaceous clay resting on it was deposited after 

 the Postglacial Optimum. From the evidence afforded by the 

 beds in the Pejark Marsh section, it appears that the scoria-cones 

 in the area were active during the arid period and spasmodically 

 during the increasing rainfall period up to less than 2,000 years 

 ago, when, approximately, the Pejark Marsh Tuff accumulated. 



Gill (1943) points out that the tuff at Warrnambool is of very 

 recent age, and gives as part of his evidence that it rests on 

 Holoeene shell-beds which means that the tuff is later than at least 

 the beginning of the Postglacial recession of the sea (if the 15- 

 foot relative rise of the land at Warrnambool is due to this 

 cause). The writer, on the other hand, believes (p. 58 jxjst) that 

 the Warrnambool tuffs accumulated earlier in the more recent 

 half of the Postglacial. 



The Hampden Tuffs, in most places, rest on buckshot-gravels 

 of lateritic origin formed during the tropical and subtropical 

 climates of the arid periods of the Postglacial and interglacial 

 stages. The flood-plain deposits of the mature Emu Creek are 

 at no place covered with scoria, a scoria-cone flow or tuff; thev 

 seem to have been at all times beyond their reach. 



