MOUNTAINS AND THEIR EFFECT ON NATIVE VEGETATION. 273 
shelter, a jungle flora may be produced on soils which are 
fairly siliceous and porous, but towards the colder latitudes, 
say from Sydney southwards, where the element of cold is 
beginning to be felt, it is found that this particular class 
of vegetation is gradually restricted to the more basic form- 
ations, with usually less than 55 to 657% silica, such as the 
basalts, the volcanic tuffs and the shales of Illawarra, and 
the igneous rocks (monzonite) of Milton. On the other 
hand, in Northern Queensland, as on Bellenden Ker Moun- 
tain near Cairns with excessive moisture and warmth, we 
find the ‘“‘brush’”’ vegetation swarming up to the summit, 
upwards of 5,000 feet, in a formation of granite containing 
about 72% silica. 
In making a comparison between the vegetation of any 
two areas, the question of soil as well as that of climate 
must be considered, and it would seem that there is a 
greater proportion of siliceous soils in Northern Australia 
as compared with those of the east, the latter being 
rendered more basic by the presence of large areas of 
Tertiary basalts. It is clear, however, that the difference 
of soils in this case is by no means the only factor in 
accounting for the difference of vegetation, for we have the 
example of Bellenden Ker on the east, with a siliceous soil 
though with the excessive rainfall of 165 inches per annum, 
supporting a brush vegetation, while in much the same 
latitude, the beautiful rich flats of the Flinders flowing into 
the Gulf, and which are formed of alluvium, a considerable 
portion of which is brought down from the basalt tableland 
to the north of Hughenden, are richly grassed and almost 
treeless. Neither is there any brush on the basalt where 
it occurs in situ near Hughenden, but on similar elevated 
formations east of the Main Divide as at the Blackall Range 
north of Brisbane, and Atherton near Cairns, the brush 
vegetation is amongst the finest in Australia. 
B—Sept. 2, 1914, 
