Land round Melbourne. 



231 



mqtlon of the strata being thus arrested, the volcanic 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 

 existed beneath the waters of the ocean. One of these ancient 

 channels leads from Flemington to CoUingwood, 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 Gambler 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 tim%, 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 harbour 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 



