To the northward of Ballarat portions of the Main Divide is of volcanic formation, and a wide sheet extending northwards finally disappears under the Post-Tertiary deposits of the Loddon Valley, and covers the ancient river-courses which trend towards the Murray River.[1]
As seen in the Ballarat district, flows of basalt followed each other, separated by periods of time which permitted the accumulation of alluviums, until finally vast areas became basaltic plains, studded with volcanic cones.[1]
The older Dividing Range is in many parts covered, and the newer river-courses do not in places accord with the older drainage areas.
Thus were formed what are known to miners as the "deep leads," trending from Ballarat northwards towards the River Murray, and southwards towards Bass Strait.
It is not possible in the present state of information to fix with any degree of accuracy when in geological time these deep leads were formed, when volcanic activity commenced, or when it finally terminated with the volcanoes of south-western Victoria and the south-east of South Australia.
The latter are placed by Professor Tate in that time when Diprotodon and Phascolomys Pliocenus were still existing, and when the flora included Casuarina and Banksia.[2]
The discovery of bones of an extinct kangaroo in the mine of the Great Buninyong Estate Company, under two sheets of basalt, suggests that the Mount Buninyong volcano may have been of the same period.
If these views are correct, it may be said that the newer volcanic era, during which the river valleys of Central Victoria were sealed up by basaltic flows, may have extended into Pleistocene time.
I have been long impressed by the fact that the "deep leads" referred to—that is, the ancient river channels—are now at considerable depths below the surface over which the
