98 GEOLOGY OF LOWER MESOZOIC KOCKS OF QUEENSLAND, 



These extensive intrusions probably resulted in the elevation 

 of the areas affected, to a much greater altitude than the neigh- 

 bouring areas. 



The Lower Mesozoic rocks of Eastern Australia appear to have 

 been deposited in a series of basins, which were not all developed 

 at the one time. The sediments deposited in these basins are, 

 with a single exception {supra, p. 38), freshwater accumula- 

 tions, and this fact tends to show that the basins must have had 

 some outlet; otherwise, the bodies of water would comparatively 

 soon have become salt. Regarding deposits formed in basins in 

 this manner, we may note that Suess quotes Richthofen's dis- 

 tinction between central and peripheral types of drainage as 

 illustrated by salt and coal. He says, " Salt with gypsum cor- 

 responds to a closed drainage system or central position; coal, 

 when found in extensive freshwater basins, corresponds to the 

 open outflow, without which no accumulation of water could 

 maintain for long its original composition.""^ The latter part of 

 this statement seems to admit of no contradiction, and it applies 

 to the basins in which the sediments of Lower Mesozoic age in 

 Eastern Australia were deposited. We shall consider later the 

 positions of the outlets for the various basins. 



The earliest basin developed was that in which the Hawkes- 

 bury Series of New South Wales was deposited. In the central 

 portion of this basin there appears to be stratigraphic conformity 

 between the Upper Coal- Measures, and the Narrabeen Stage of 

 the Hawkesbury Series. Nearer the margins, however, there is 

 unconformity. In addition, there is a very distinct palaeonto- 

 logical break, only a few forms persisting from the lower to the 

 upper. The unconformity between these two Series is one which 

 involves a detinite interval of time, but not any considerable 

 movement. The time-interval must have been sufficiently long 

 for the Mesozoic flora of the Narrabeen Stage to have almost 

 completely replaced the typical Palaeozoic flora of the Upper 

 Coal-Measures 



The basin in which the Narrabeen Stage was deposited was 

 produced by a gradual subsidence, which apparently continued 

 * Suess, "The Face of the Earth,'" iii., p. 312. 



