Land round Melbourne. 231 
motion of the strata being thus arrested, the volcani¢, power 
expended itself in upheaving them from the bed of the ocean, 
the higher portions of land eastward of Elizabeth Street, being 
thus elevated above its surface. The lava however, not yet 
cooled, and still subjected to a considerable hydraulic pressure 
(which is manifest from the occurrence of porous discoloured 
basalt, below the dense black basalt which is found cropping 
out from the surface in so many localities,) spread itself over 
the country by means of the numerous gulleys which already 
éxisted beneath the waters of the ocean. One of these ancient 
‘channels leads from Flemington to Collingwood, between the 
Botanical Gardens and Government Paddock, thence beneath 
Prince’s Bridge, towards Emerald Hill. The two varieties 
of basalt just mentioned, owe their specific characters either 
to hydraulic pressure in the manner described above, or 
otherwise are derived from the union of silica and calcium 
in a molten state; when these ingredients are combined in 
quantities such that the ratio of the oxygen of the calcium, 
to the silica be as 1:2, or even 1°3, to unity, a crystalline mass 
is produced, resembling dense basalt ; but when the proportion 
is 1:4, a porous matter similar to amygdaloidal basalt is 
obtained. 
Such is my explanation of the primary cause of existence 
of the extensive basalt formation in the country north and 
west of Melbourne, and between Flemington and Williams- 
town. The same theory applies to the whole district between 
Melbourne and Mount Macedon, as also between Mount 
Alexander and the new Sydney Road; in fact I was led to 
form this theory while travelling from Mount Gambier on the 
frontier of South Australia, where the proofs of its correctness 
are strongest, becoming fainter as the traveller progresses 
eastward. 
The crater, though still buried beneath the ocean, retained 
its tremendous power for a considerable time, but was finally 
overpowered and extinguished by the agitated sea, which 
pouring into the crater, and becoming comparatively calm, 
deposited in it a vast quantity of mud and sea weed; ulti- 
mately a placid lake as it were, rested on the bosom of the 
extinct volcano, and innumerable multitudes of shell fish found 
in it a secure harWour in which they could, without molestation, 
propagate their species. The Yarra and Salt Water Rivers 
however, again disturb the tranquility of the scene. Each 
directing its course to the lake, their united current sweeping 
over it, eventually filled up the crater with alluvial deposit, 
and entirely buried the marine animals which had found a 
