^Igli ] Excursion to Korkuperrimul Creek {Bacchus Marsh) . 5 



EXCURSION TO KORKUPERRIMUL CREEK (BACCHUS 



MARSH). 

 Quite a large party, including several ladies, met at Spencer- 

 street station on Saturday, 23rd March, in order to take the 

 7.40 a.m. train to Bacchus Marsh. During the train journey 

 the immense level plains of Newer Basalt over which we passed, 

 and the almost circular hollow in which the town of Bacchus 

 Marsh has been built, were duly noted and commented upon. 

 The weather was ideal, and as the party walked through 

 Maddingley Park towards the township, and afterwards along 

 the Ballan road, the sunshine, tempered by a slight breeze, 

 enhanced the outlook and rendered the outing decidedly 

 pleasant. The early part of the excursion was along 

 the route of an excursion taken some two years ago by 

 University students under Professor Skeats. At a suitable 

 point a halt was called, and the geological history of the 

 district, with the resulting physiography, studied. The dark, 

 densely- wooded hills in the distant north-west were pointed out 

 as the bedrock of the district, being composed of shales and 

 mudstones of Ordovician age, and of the Castlemaine horizon. 

 In striking contrast were the nearer treeless slopes of Bald 

 Hill, the material of which was deposited in Permo- 

 Carboniferous times. The bedrock, during the great Devonian 

 earth movements, had probably been folded, faulted, and 

 pierced by igneous dykes, followed afterwards by a long period 

 of erosion. Next, in the Permo-Carboniferous period, an 

 immense ice-sheet moved northwards over the area from a 

 hypothetical point in the Antarctic, and deposited the 

 argillaceous sediment of Bald Hill. Turning more to the 

 west were the sloping yet steeper hills of Older Basalt. 

 In Mesozoic and Cainozoic times the district had probably 

 remained a land area, and the great volcanic activity which 

 followed was shown by the immense thickness of the floor as 

 indicated by the hillsides. This outpouring disturbed the 

 drainage system of the area, and a huge fresh-water lake was 

 created, on the banks of which grew trees similar to the cin- 

 namons and laurels now growing in Queensland and New South 

 Wales. After this lacustrine period the Newer Basalt flows 

 connected with renewed volcanic activity of Pliocene age once 

 more overwhelmed the area, filling up the old streams. Thus, 

 where we stood in the road-cutting we could see the old river 

 sands and gravels exposed, whilst as far as the eye could see 

 — east, south, and west — were the Newer Basalt plains, with 

 their steep edges towards the Bacchus Marsh basin. Then 

 further changes took place. A big fault-scarp occurred in the 

 Ordovician series, which was visible along the eastern slopes of 

 Bald Hill, and extended a considerable distance either way. 



