84 
Geology and Physical Geography; 
With re-submergence the deposit of the Mesozoic rocks 
commenced and continued during long ages of gradual depres- 
sion, till a flanking deposit had been formed skirting the main 
mountaiu system, from the Wannon to Port Phillip, and from 
Western Port to the Macalister, to a height not less than 
2,500 feet above the present sea-level. This does not neces- 
sarily imply that every hill or spur of older rocks now under 
that altitude was then covered. The slopes of the main mountain 
system were then less denuded than they are now, and a contour 
line at 2,500 feet above that of the present shore lino would have 
been far nearer to the latter, measuring horizontally, than it is now. 
The Silurian rocks and granite of Cape Liptrap and Wilson's 
Promontory indicate the approximate position of part of the 
southern margin of the eastern portion of the Mesozoic basin, but 
it would be impossible without more accurate knowledge of the 
geology of Tasmania and of the islands in Bass 3 Straits to form a 
conjecture as to the boundaries on the south-east and south-west. 
There is nothing to show what formations were deposited on the 
north of the Main Divide during the Mesozoic period, unless the 
conglomerates of the Wild Duck Creek belong thereto. Any 
extensive deposits that may have existed have been removed, unless 
some remain concealed beneath the Tertiories bordering the Murray. 
The conditions under which the Mesozoic rocks were deposited 
do not appear to have been altogether marine, but rather fresh 
water or brackish, merging into marine. The conglomerates, at 
the edges of the Mesozoic areas, speak plainly as to the vicinity 
of the land surface of the period to the localities where we now 
find them. The character of the fossil flora and of the few fossil 
fauna yet found tell the same tale. We may regard the Mesozoic 
rocks ns deposits — in previously eroded basins — of sand, silt, mud, 
&c., brought down from the land surface and arranged by shallow 
waters, whose currents were fluctuating both in direction and 
power. The land was in process of slow submergence, and, as it 
sank, the material derived from its wasto continued to be arranged 
by marine or lacustrine action in layers of varying thickness • 
sometimes evenly, sometimes uneveuly bedded, forming over-thick- 
ening accumulations around the land-margin, near to which larger 
fragments brought down from the land were rolled and arranged 
by littoral action in the form of conglomerates. 
Intervals occurred during which the conditions were favorable 
to the accumulation in swamps ami low-lying shallow basins of 
growing or drifted vegetation, subsequently covered by further 
layers of saud and silt, ami altered to the form of coal. 
These processes went on until the submergence lmd attained its 
limits, and the laud began to rise again. From this period com- 
menced a denudation of the beds which had been deposited, and 
the erosion in them, and in older rocks, of new and deeper hollows 
or channels, which were destined in their turn to he again partly 
filled by the accumulations of the Tertiary epoch. 
