Geological History during Tertiary Epoch. 
109 
BALLARAT. | GIPPSLAND. 
Upper Pliocene Period . 
Gradual rising of land surface. Marine and estuary formations in pro- 
gress on receding coast-lino. 
Alternate lava-flows and sedimen- 
tary deposits, the last flows covering 
n-nd nearly obliterating the ancient 
drainage lines, after which rivers 
began to cut new courses through 
the basalt. 
Fluviatile and atmospheric action 
continued. Rivers cutting deeper, 
and, in the higher country, to below 
the level of the ancient streams. 
Post Tertiary. 
Recent and Most Recent. 
Fluviatile and atmospheric action 
continued. Rivers cut their way 
through the lava-flows down to their 
present beds, forming alluvial flats 
as at present. 
Fluviatile and atmospheric action 
continued. Rivers eroded their 
courses to present depth. Deposits 
of Gippsiand plains completed, and 
lower flats and morasses formed 
along margins of rivers. 
The Newer Volcanic lava-streams which poured from so many 
points of eruption throughout the western part of the colony 
partly or wholly filled up and concealed the rivers of the period, 
forming wide strips occupying the valleys from side to side in the 
hilly areas, spreading in broad sheets over the lower lands, and 
forming the great basaltic plains which constitute so important a 
feature in this country. 
The occurrence at Ballarat of four distinct layers of basalt, 
separated from one another by tolerably thick sedimentary accu- 
mulations, shows that a very long period must have elapsed from 
the commencement to the close of the newer Volcanic period. 
The basin of the Yarra affords an illustration of the successive 
effects of the agencies, both aqueous and volcanic, which were in 
operation during the Middle Tertiary and Upper Tertiary periods 
respectively. 
We have in the remnants of Miocene gravels, covered by 
patches of Older Basalt, at Hod die’s Creek, and from there to 
Lillydale, at the Kangaroo Ground, and near the Saltwater River, 
the vestiges of a Miocene river system, draining approximately 
the same country as that now traversed by the Yarra and its 
tributaries, the Plenty and the Saltwater Rivers. 
That the mouth of this old river was in the vicinity of Mel- 
bourne is shown by the Older Basalt occurring from Emerald Hill 
to Flemington, and evidently filling in an estuary of the Middle 
Tertiary period, though the connexion of this basalt with the 
patches up the Yarra Valley has been severed by subsequent 
denuding action. The partial filling up by Older Volcanic lava- 
flows of the river course, and the changes effected by littoral 
action during the earlier Upper Tertiary submergence, caused a 
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