Page:A sketch of the physical structure of Australia.djvu/49

37 similar character. Upon these highly inclined strata repose at various places beds of a tertiary formation. These were well shewn a little south of St. Kilda, and at Brighton a mile or two beyond. The tertiary rocks here were composed of a brown ferruginous sandstone, commonly soft and friable, but often containing and sometimes passing wholly into a hard dark mass of ironstone more or less metallic looking and always concretionary. In other places the sandstone instead of brown is white, or red, or mottled with those two colours in various portions. These characteristics precisely resemble those of the rocks about Port Essington, on the north coast of Australia. The rocks of Port Phillip, however, often contain lines of fossil shells, mostly in the state of casts, these were chiefly referrible to the cultellus, amphidesma, donax, tellina. nucula and littorina, there were also numerous specimens of a small spatangus, and leaves of a dicotyledonous tree, very like eucalyptus in appearance. The thickness of these rocks exposed in these cliffs of "Brighton" was about 40 or 50 feet, the beds being horizontal.

The only other rock seen about Melbourne was a heavy hornblendic trap or lava, sometimes very heavy and compact, but often cellular and even scoriaceous, with all the appearance of recent subaërial lava. This rock is very largely diffused over the country as far as 12 miles N.E. of Melbourne, often occupying the valleys and lower grounds, and making a rough uneven surface, bristling with lava blocks. The higher grounds appeared to me to be usually of white sandstone. In some instances this lava seems to have flowed down the existing valleys of the country. The valley which comes down from the Moonee ponds into the salt lagoon near Melbourne, has on each side of it a high terrace of sandstone. Between these banks the bottom of the valley is entirely occupied by the trap or lava, in which has been excavated the present bed of the river, or whatever water it is that comes down the valley in seasons of flood.