54 



AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 



formerly emptied into lakes and the sediments now covering their 

 lower reaches are covered with lava. The scoria-cone flow over 

 the western one is evidently very recent, for the subsequent 

 streams have not yet become marginal streams ; the lava in places 

 is a narrow flow that appears to have occupied a small gutter cut 

 in fluviatile deposits. The lava covering the sediments over the 

 eastern trunk-stream appears, on the other hand, to be older, for 

 fairly mature lateral valleys have been formed along its margins. 

 Some of the tributaries of this eastern trunk stream have been 

 dammed back by encroaching lava, a lake has been formed, and 

 lacustrine sediment deposited on the tributary flood-plain. Such 

 has occurred at Talbot (Back Creek) 8 miles to the south, where 

 the remains of Diprotodon were found supposedly in diatoma- 

 ceous lacustrine deposits (Keble, 1945). 



Myrniong C K 

 P 



Werribee River 

 V 



wm L c 



P a I a e o zo L c rocks 



FIG. 7. 

 Section through The Island, Myrniong. 



The absence of information as to what bed the axehead came 

 from makes its age uncertain but the geological history of the 

 area indicates the Recent or Postglacial. 



The Myrniong implements from The Island, 6 miles N.W. of 

 Bacchus Marsh, were found in a bed of gravelly clay (X, Fig. 7) 

 18 inches thick underlying basaltic lava, by C. C. Brittlebank, 

 Government Plant Pathologist, who was also a skilled and reliable 

 geologist. The Island is so-called because it is a high lava-residual 

 almost separated from the rest of a scoria-cone flow by the deep 

 erosion of marginal valleys, the streams in which almost junction 

 at its north-west end and actually become confluent to the 

 south-east of it. A section of the lava-residual is shown in Fig. 7. 



The pre-basalt valley, PBV in Fig. 7 was filled with basaltic 

 lava to the level PV after which, to find an outlet, the drainage 

 started to erode in the less resistant rocks at P and V, channels 

 that have developed into deep marginal valleys. That developed 

 at P, the Myrniong Creek, is now 430 feet below the original sur- 



