BY H. I. JENSEN. 



71 



•dew and atmospheric vapour cannot find their way down. For 

 these reasons, the forest-flora, specially adapted for the silicious 

 porous soils, has never been able to transplant itself to the basalt- 

 areas. 



It is also possible that the cracking of these heavy soils, in dry 

 weather, may fracture and tear tree-roots to such an extent, that 

 forests are unable to establish themselves. 



C— The Basalt Knolls of tlie western interior owe their bare- 

 .ness to two causes. In the first place, basalt is such a compact, 

 homogeneous, and even-grained rock that, in an arid climate 

 where organic acids (from decomposing vegetation) and moisture 

 are at a minimum, decomposition is extremely slow. Granite, 

 porphyry, and sandstone are much more readily disintegrated by 

 heat and frost. In the second place, the minerals of basalt are 

 all decomposed with about equal readiness, there being no 

 specially hard and resisting mineral, like the quartz of granite. 

 Therefore, the soil formed by the disintegrating basalt is very 

 .finely divided, and is readily blown away by the wind. The 

 wind practically removes the soil as fast as it is formed, on the 

 basalt knolls of the arid interior. 



D.— The basalt-ranges of the south of New South Wales along 

 •the coast, differ from the Queensland ones in having a colder 

 -climate, and lower rainfall, two factors which prevent a semi- 

 tropical, true scrub from establishing itself. Rapid corrosion 

 and erosion, unhindered by dense vegetation, have given rise to 

 steep slopes, which again have been the cause of such an excellent 

 natural drainage, and such a stony soil, that forest-vegetation 

 lias had no difficulty in asserting its supremacy. 



The basaltic ridges of the Little Liverpool Range and Fassifern 

 District of Southern Queensland owe their forest-flora to a similar 

 •cause. The climate of this region is much drier than that of the 

 coast, but wetter than the Darling Downs, whose eastern flank 

 is formed partly by these ridges. Springs never occur herein the 

 basalt-lavas, and the slopes are steep. Consequently we have 

 here conditions intermediate between those of the scrub-decked 

 -coastal basalts, and the bare plains of the Downs. The soils. 



