COLONIAL GEOLOGY — MELBOCBXE. 
33 
with a corresponding submersion. At the immediate junction of the 
lately-described Upper and Lower Tertiary beds, for example, not only is 
the upper surface of the latter water worn, but the rock itself, for many 
feet in depth, is fretted into numerous fissures, subsequently filled up with 
material exactly corresponding with that comprising the rock above ; thus 
a distinct proof is afforded of the underlying rock having formed an old 
coast-line, or at least a rocky eminence nearlj^ awash with the waves, from 
which position the whole afterwards sank sufficiently deep below the 
water to allow of nearly 20 feet of newer strata being deposited at a later 
period. 
Still further proof of these changes of level is afforded by certain for- 
mations around Geelong, at which place thick beds of limestone, contain- 
ing Planorbis, Lymnea, Paludina, and other limestone and fluviatile shells, 
appear above Miocene and beneath nearl}- 20 feet of Marine Pliocene de- 
posits ; thus necessitating an upheaval over a portion of the country 
large enough to allow of freshwater lakes being formed, and a subsequent 
submersion of the whole district, in order that the marine strata might be 
thrown down. 
These continued elevations and depressions of surface are not a little 
puzzling to the tyro scarce willing to admit the possibility of any such 
phenomenon in a single instance. The district, however evidently vol- 
canic, would appear to have been especially subject to the changes spoken 
of, — a rise generally preceding, and a submersion succeeding, each out- 
burst of lava. ]S"or is it at all improbable, from recent observations, but 
tliat the land over the whole of Port Phillip Bay is still rising,* whether 
to be followed by a renewed outpouring of igneous rocks and a fresh sub- 
mersion is beyond the power of science to foretell. 
No account of tlie Melbourne district would be complete without some 
mention of the Basalt — the lefe noire of the miner, the material of half 
our public buildings, the substratum of so many Australian plains, the 
core of so many of our hills, and the allowed source of the colony's fer- 
tility. This particular rock is of various ages ; no less tlian three different 
intrusions or outflows are traceable on the map annexed. The newer or 
Basalt proper about Victoria, in vast irregularly-shaped patches. On care- 
ful exploration, these generall}^ show traces of having been ejected in some 
higher portion of the land, tilling up the adjacent valleys with a once 
molten but now solidified mass. At first view, few mineral substances 
would seem less capable of being acted upon by the elements. Yet the 
fertile soil, composed wholly of basaltic clay and sand, together with huge 
boulders, masses left by the decomposition of the rock around them, 
show that so indurate a material is by no means proof against such com- 
paratively weak forces as atmospheric actions. The denuding power of 
water is also strikingly shown where the Merri Creek has cut its way in 
a channel, 60 feet deep, through basaltic beds for many miles. Still more 
remarkable is the denudation of the Keilor Valley. At this place, not 
only has the Basalt been removed, but 20 feet of Tertiary, and from 30 to 
40 feet of Silurian rocks have been cut through also ; thus leaving a 
number of semi-detached hills, each having a base composed of shales and 
Palaeozoic sandstones, strangely distorted by ancient convulsive move- 
ments ; a middle portion, formed of Tertiary deposits, lyingun conform- 
ably upon the older rocks below, and on their summits a thick capping of 
* The ' I.ightQiug,' Black Ball liner, lately struck upon a rock near the Heads, 
which had never been laid down in any chart, probably because the depth at which it 
lay had decreased since making the fiust survey of the channel. 
VOL. VII. r 
