62 
The Tertiary Beds. 
From the general aspect of the Tertiary beds on French Island it may be 
inferred that they were at no distant date continuous with similar beds on 
the mainland. Besting on these Tertiary beds, but possibly of Post Pliocene 
age, are quartz gravels such as occur about \ mile south-west from Mount 
Wellington. This quartz gravel was no doubt laid down when the island was 
connected with the mainland, and possibly it corresponds with the Post 
Pliocene gravel on the Divide between Grantville and the Bass River, which 
possesses some features of special interest. The Grantville and Bass River 
series consist of well-rounded and polished quartz pebbles, the polishing 
seemingly due to glacial action. Besides quartz there are pebbles of chert, 
agate, jasper, silicified wood, &c., also in places many small sapphires. 
Similar gravel occurs at intervals along the south coast. There can be little 
doubt that it was ' deposited contemporaneously with the Post Pliocene 
glacial action that took place on a large scale in the Lake Dora district, on the 
west coast of Tasmania, and in the South Island of New Zealand. 
If the quartz gravel resting on the Tertiary beds of French Island corre¬ 
sponds with the Post Pliocene gravels on the mainland, it is possible that the 
island was not detached from the mainland until after this Post Pliocene gravel 
was laid down, or, in other words, the period at which Westernport Bay was 
formed is fixed as not older than Post Pliocene, and stretching down to Recent 
and the present time, for the work is still in progress. 
As the quartz gravel must have been laid down under water, it would 
appear that at that period even French Island and the surrounding country 
were submerged. Since then there has been an uplift, which has raised the 
later Tertiary beds and their overlying gravels to heights varying from a few 
feet up to between 350 and 400 feet above sea-level. This uplift has not been 
general, however, and it appears to have been compensated for by subsi¬ 
dences in other parts. At Sorrento, on Port Phillip Bay, boring has proved 
that since the Recent period began considerable subsidence has taken place. 
In both Westernport and Port Phillip Bays earth movements resulting 
in general subsidence have doubtlessly exerted a considerable influence in 
their formation. Near San Remo, above the beach, north from that locality, 
there are beds of Jurassic rock that are standing nearly vertically, while on 
the shore the beds are inclined at a low angle. Erosion, the result of differ¬ 
ential earth movements, is accountable partly for these two bays as they now 
exist. For although the general aspect around the shores of French Island 
is that of a sinking area, erosion is more accentuated along some portions of 
the shore than others. That portion of the east coast line between Mosquito 
and Brella Creeks is being rapidly gnawed away by the sea, and the falling 
and prostrate trunks of trees along the beach testify to the rapidity with 
which the land is being encroached upon. 
The great subsidence that has taken place at Sorrento within the Recent 
period is quite sufficient to account for the presence of Bass Strait between 
Tasmania and the mainland. There is, therefore, no need to place the separa¬ 
tion of the island from the continent at a period more remote than the Recent. 
[4.19.10.] 
NOTES ON DOOKIE. 
By E. J. Dunn, F.G.S., late Director, Geological Survey. 
The greater portion of the parish of Dookie is occupied by rocks of the 
Heathcote series, principally diabase. The surface is diversified by hills that 
rise to 750 feet above the general level. A low range runs northward and 
