22 
THE GEELONG NATURALIST. 
TDottom. The Eagle Eock at Airey's Inlet rests on basalt, which 
appears to have been the sea shore of the eocene sea, as even the 
fossil limpets are mixed with cowries and other shore loving shells, 
such as we find around our present rocky coasts. These gradually 
make way for deeper sea forms, until the whole of the superior 
rocks consist of nothing but polyzoa, terebratulas and echinoderms, 
enclosed in the limestone of the district. It is quite probable that 
when the basalt was the shore at the Eagle Eock, the coast around 
Spring Creek was low lying land, favourable to the deposition of 
mud on which shells lived. The gradual lowering of the land would 
then account for the great depth of this deposit ; the coast at 
Eagle Eock being a rocky one, no depth of littoral shells is found. 
At Spring Creek the polyzoal rock does not overlie the littoral 
deposits as at Eagle Eock, and the reason of this requires more 
study. But we can scarcely doubt this portion of our coast shell 
deposits was built on a lowering land, for we must remember that 
the shallow water shells underlie the deeper sea forms at Eagle 
Eock. One noticeable feature of the Spring Creek bed, is that the 
fossil shells shew, according to Prof. Tate and J. Dennant, a 
greater percentage of miocene shell than some others of our 
eocene deposits, which of course would make it slightly younger. 
Birregurra township is, as the crow flies, about 10 or 12 miles 
north- we«t from Spring Creek. Standing on the highest point at 
Birregurra, and looking from there towards the sea coast, we can 
trace a valley of depression with several ancient mouths or open- 
ings leading to the sea. One of these mouths occurs at Airey's 
Inlet, another tends to Spring and Bream Creeks. At several 
points in this low-lying area, where the water has cut through the 
fresh water drifts and gravel beds, it has exposed the underlying 
polyzoal rocks ; as for instance on Hopkin's station near the bridge, 
at Laketown, about half-way between Birregurra and Spring 
Creek, and on Ingelby station about 5 miles south-west from 
Birregurra, about half a mile up the river, the fossil bed known as 
Bowden Point, stands on the edge of the valley aforementioned, 
and at a distinctly higher level than the exposure of the limestone 
rock, which may possibly indicate that it is younger than the beds 
beneath (the limestone). The evidence of the fossils found, supports 
this conclusion, there being a greater percentage of miocene forms 
in this bed than in most of the others. At Spring Creek there is 
apparently a small deposit of similar shells, which occupy a 
higher level than the principal beds, but these shells are chiefly 
fragments washed down the face of the cliff after rains. There 
cannot be much doubt that the Birregurra, like the Belmont bed, 
was deposited on a rising sea bottom. In regard to this last bed, my 
notes taken at the time, are that some of our townsmen, thinking 
to find fire clay, set men to work to sink a shaft on the highest 
portion of the hill, about 20 chains on the west side of the Colac 
Eoad, in a paddock, which in the celebrated boom time was styled 
