130 THE SOUTH AUSTRALIAN FLORA. 
most strongly-marked form, the distance between the bottom of the 
cavity and the level of the surrounding ring scarcely amounts to five 
feet. The continual change of level produces a very broken surface, 
which, however, becomes effaced in the course of a few years under the 
plough. The Flora of these districts has some peculiarities, Whilst 
in other tracts which I have visited, grass-land destitute of trees is com- 
paratively rare, these districts show a decided aversion to the elsewhere 
almost universally prevalent Eucalyptus, which here seldom occurs except 
as a border to the ravine-like water-courses, and even then only as a less 
robust species, Eucalyptus odorata, Schldl. Casuarina is a more com- 
mon shrub, but the commonest is Acacia pycnantha, which here evinces 
an unusual tendency to unite in groves. Bursaria is also characteristic 
of these localities, together with the creeping bushes of a few Grevilleas. 
The generally treeless ground is peculiarly rich in Syngenesious 
plants ; but, with the exception of the Grasses, poor in Monocotyle- 
dons. Orchideæ it does not produce at all. 
A second variety of the vegetation of the grass-land is afforded by 
the beds of rivers when dried up in summer. The stems of the Fuca- 
lypti on the banks attain here to incredible dimensions; trunks of 
eight feet diameter being by no means uncommon. Crowded together 
in the actual bed of the stream, is a Flora of principally European 
forms, which, hitherto retarded by the water flowing over them, first 
develope their flowers when all others are withered. The bed is like- 
wise often filled up with bushes of Melaleuca or Leptospermum. Reeds 
and brushwood, hanging from the tops of these bushes, then mark the 
height to which the water rises in winter. This form affords the tran- 
sition to another—that of those shady ravines, which, during the whole 
year, are more or less supplied with water. Here is found a vegetation 
whose herbaceous representatives generally remind us of Europe, even 
more strongly than those of the dried-up creeks and of the remaining 
grass-land ; but whose arborèscent and fruticose forms assume the 
habit of the Scrub-land. But as this Flora occurs for the most part 
in the transverse valleys of the upper course, seeds, rhizomes, &c., are 
carried down during the winter rains, and enrich the originally different 
Flora of the ill-watered lower course. 
The Scrub differs from the above-described forms of vegetation by 
the utter want of a turf; at least, I do not think that the most imagi- 
native colonist could construct a turf out of the few scattered Stipas 
