196 Proceedings of the Royal Society of Victoria. 



gravel which, though pi'esent in the Coiaiaidai series, may be 

 better observed in the Korkuperrimul Creek sections. 



In conclusion it may be noticed that though the beds of the 

 Coimaidai area show less complexity of structure than those 

 exposed in the Korkuperrimul Creek, yet they must be regarded 

 as part of the same series ; similar general conditions probably 

 prevailed over the whole Bacchus Marsh area, but in the country 

 west of the Lerderderg River certain special conditions appear to 

 have prevailed, the influence of which only partially, if at all, 

 extended to the Coimaidai district. Their lacustrine origin under 

 the action of an ice-sheet moving from the south is the feature 

 common to all the beds, but the frequent occurrence on difterent 

 horizon of boulder-beds separated by deposits of sandstone and 

 conglomerate along the Korkuperrimul Creek points to a 

 considerable variation of conditions during the gradual formation 

 of the beds. The repetition of beds may be explained by climatic 

 advances and recessions of the ice-front, and possibly in the area 

 W. of the Lerderderg River there may have been considerable 

 oscillations of level. JMuch evidence has been collected of late 

 years to show that glaciers can move over loose and incoherent 

 deposits without disturbing them, and Professor Geikie has ably 

 argued tluit under certain conditions a glacier may cease to be 

 erosive. Though a certain amount of contortion of the beds 

 along the Korkuperrimul Creek has been noticed by Professor 

 David, thei'e is on the whole a striking absence of disturbance of 

 the softer beds of the glacial series ; an explanation of this feature 

 may be found in the sub-aqueous formation of these beds. 



EXPLANATION OF PLATE8. 



Plate VIII. 



Sketch Map of Coimaidai. 



Plate IX. 



I. — Section through tertiary beds near Alkemade's Quarry. 



(1) Magnesian limestone, with partings of clay and gravel, 

 and containing fossil marsupial bones. 



(a) Thin band of volcanic ash, interstratified with 

 (1). Tl\e fossil bones occur below this. 



