80 ON THE DEEP OCEANIC DEPBESSION 



The conformation of the part of the ocean-bed off Moreton Bay, 

 as thus explained, is due to purely geological causes, of which 

 the existence is illustrated by the escarpments and ravines yet 

 extant on the land — the ooze and clay and coral sand brought up 

 by the sounding apparatus and dredge being mere submarine 

 superficial deposits, covering and partly filling the bottom of the 

 depression. This analogy of conformation between the depths of 

 the sea and the heights of the land is parallelled by the distribution 

 of life (as has been shown by Dr. Hooker) on the ocean ridges 

 and depths, only in reverse order to that on the land. " The 

 ocean," he says, " thus mirrors one of the most striking features 

 of the distribution of terrestrial life, and, mirror-like, it turns the 

 picture upside down." 



If we travel inland from Cape Moreton on the same general 

 bearing exhibited before, we shall find an almost equal slope from 

 the high lands at the heads of the drainages to Moreton Bay as 

 appears on the slope of the Blue Mountains towards Port Jackson; 

 for in 1853 I made the elevation of the granite domes near Mary- 

 land, by barometrical observations, 3,727 feet, and the dividing 

 range between the Condamine and Dumaresq E-ivers, at the head 

 of the latter, 3,120— Mount Melbourne being 3,829, and Mou- 

 bullon, or Craig's Eange, 3,640 feet — Mount Cordeaux, according 

 to Cunningham, being 4,100 feet, which is very near the height of 

 the land above the tunnel on Mount Clarence, which itself is 

 3,658 feet. The relations of land and sea appear then to be 

 nearly exactly equivalent to those in the southern coast region of 

 New South Wales, since, though there are higher points in New 

 England and in Maneroo, than those already mentioned, yet the 

 general elevations are much the same in both districts, and as off 

 Moreton Bay there is a deep depression, so there is another off 

 Mount Dromedary and Twofold Bay. What relation these 

 depressions have to each other is not yet fully ascertained ; but it 

 is nearly certain that the bases of New Holland and New Zealand 

 meet somewhere about half way between them, and the stages of 

 ascent are precipitous or with long inclined slopes, the deepest 

 depressions lying as it were on each side of a submarine plateau. 



In my view, the combined phenomena as exhibited by the 

 Opposite coasts of these countries (which formerly extended further 

 into the ocean) — by coral reefs and other conditions — induce the 

 conclusion that great rents and denudation in the earliest periods 

 of our geological history were the result of depression and sub- 

 mergence, affording channels for ocean currents, deep receptacles 

 for cold stagnant water, and passages for such surface currents as 

 that which bathes New South Wales with a stream warmed in 

 latitudes nearer the Equator than that of Sydney or Brisbane. 

 Much of the history of that stream has to be discovered, but the 

 fact elicited respecting the submarine vaUey north-easterly from 



