THE VICTORIAN NATURALIST. 81 



the Lerderderg on the north and the Brisbane Ranges on 

 the south has been an extensive basaltic plateau, with a fall 

 of over 1,200 feet from north-west to south-east. Probably 

 the basalt has been poured forth from the volcanic vents 

 to the west of Bacchus Marsh — viz., Mounts Blackwood, 

 Ingliston, Goorong, and Daraweel. A peculiar feature in this 

 flow is that at a point 2^' miles west of Bacchus Marsh it has 

 descended a slope of over 300 feet, and then spread over an area 

 thousands of acres in extent. The officers of the geological 

 survey refer to this as follows : — •" It rises abruptly 300 feet from 

 the lower basaltic plain to the high table land, and at this point a 

 good section is exposed. A similar feature must have existed in 

 the Miocene formation prior to the flow of Newer Basalt." This 

 ridge can be traced for about 6^ miles to the south-west. The 

 present drainage system has cut deep gorges, gullies, and wide 

 valleys through the basalt and underlying beds. Sections of the 

 Miocenes are to be seen in the valleys of the Werribee, Parwan, 

 and Pyke's Creek ; on the main Ballarat road, between Bacchus 

 Marsh and Pyke's Creek, and to the south and north of Myrniong. 

 In the valley of the Werribee, west of Bacchus Marsh, a section 

 is exposed for about 4^ miles east and west. 



Along this section the Miocenes are composed of white and 

 yellowish-white clays, grits, waterworn quartz gravels, and sandy 

 clays. Through this section are various-shaped masses of 

 ferruginous sandstone, which in some instances contain the 

 casts of leaves — Laurus Werribeensis, Cinnamomum poly?)iorph- 

 oides — together with casts of fruit. Several bands of white clay 

 retain the casts of the abovenamed and various other plants. 

 At the east end of the above section, and west of Bacchus Marsh 

 about two and a half miles, the Miocene beds are probably 300 

 feet in thickness. From this point west they gradually thin out be- 

 tween the uprising older rocks and the Newer Basalt. The highest 

 point reached by the Miocenes on this section is about 975 feet. 

 Clear sections are of rare occurrence, owing to the thick coating 

 of " talus " derived from the Newer Basalt and the beds under 

 notice. Fortunately miners have driven several tunnels into the 

 hill under the basalt. The sections exposed in these, though 

 small in extent, show that, as the older rocks are approached, the 

 material forming the Miocene beds increases in size. A section 

 in one of the drives shows the following section resting upon 

 glacial drift : — 5 feet yellowish-white clay — probably derived from 

 the underlying Glacial Drift ; 2 feet 6 inches heavy boulder wash, 

 2 feet 6 inches coarse gravel, 3 feet fine sand, 2 feet quartz 

 pebbles and sand, basalt about 90 feet. At the entrance of one 

 of the tunnels a small almost vertical dyke cuts through the 

 Glacial Drift, but does not penetrate the overlying Miocenes. 



A section on the north bank of the Werribee, and directly 

 south-east from the Trig, station — known locally as " Hat Island " 



