GLACIAL DEPOSITS OF BACCHUS MARSH. 881 



this section is capped by the old river bed terrace. The next section 

 up the stream is one of blue-grey clay, with bands of sandstone 

 about 4in. thick running through it ; the stratification is very even, 

 except on the south, where a slight bulge upward is seen 



The erosion of these river valleys has been effected since the 

 basaltic overflow, and therefore since the so-called Miocene leaf- 

 beds — which underlie it — were deposited. They could not have 

 existed as valleys at the time of the basaltic overflow, or the 

 viscous mass would have flowed into them, and that being now by 

 far the harder rock, the pi'esent valleys would certainly not have 

 been identical with the former ones. 



South-west of Dunbar Farm, in the Myrniong Creek, and in the 

 Korkuperrimul Creek from west of the large quarrj', occur deposits 

 of basalt that descend to a much lower depth than usual, and 

 occupy what were jjrobably ancient valleys, being over 400ft. in 

 thickness ; but the creek sweeps over and around it, or erodes 

 narrow courses only through it, as it forms barriers difficult to 

 erode, and something of this kind would be anticipated wherever 

 the present watercourses approached the ancient valleys which had 

 been filled with the overflow of basalt. 



In the paper (referred to above) of Messrs. Officer and Balfour it 

 is mentioned that the first section they examined was situated on 

 the Ballarat-road, about three miles on the Ballavat side of Bacchus 

 Marsh, and is at a height of about ToOft. above the sea, which is 

 some SOOft. higher than the small quarry. They state that the 

 deposit exposed consists of a matrix of clay of a quite unstratified 

 appearance and of a somewhat variable consistency. It is tough 

 and hard in places, while in others it is soft and less tenacious. 



This deposit had, previously to those gentlemen visiting it, been 

 examined by ourselves, as also since, and we find that it is strati- 

 fied and the dip is 25^^ E.S.E. Its variable consistency, described 

 as being " tough in places, while in others soft and less tenacious," 

 is caused by the denudation of the higher stratified rocks, which 

 have decomposed, and some have fallen down on to the sides o£ 

 the cutting ; so that instead of a Tertiary " till or boulder-clay 

 backed up against stratified silicious sandstones — really overlying 

 them " — being stamped as of glacial origin by " the unstratified 

 nature of this deposit, together with the peculiar nature and want 

 of arrangement of the included stones," it is rather stamped by 

 these conditions as "talus." We have simply the stratified rock 

 (Triassic sandstones), mudstone, and sandstone, including in its 

 mass boulders of granite (one about 18in. in diameter lying on the 

 road side) and very hard dark-colored quartzite, and the sorts of 

 stone before mentioned, intercalated with beds of pebbly con- 

 glomerate. It is the mudstone rock that is exposed here, and the 

 stones are scattered somewhat, irregularly and are of various sizes 

 and sorts, round and sub-angidar. The angularity of the fragment 

 of sandstone described as occurring in this cutting is caused by 



