190° A. G. HAMILTON. 
of the trees are laid bare, and some fall through being deprived 
of support, while those which do not fall have to suffer from the’ 
summer’s heat and the winter’s cold acting on their roots ; they 
become unhealthy and gradually die, their deaths being accelerated 
by the attacks of various parasitic enemies, fungoid or insect, 
which find a suitable habitat in the diseased plants. When steep 
hillsides have been cleared, the roots left in the ground decay, 
and the binding together of the particles of mould which they 
effected is lost; when a wet season comes, the upper soil resting 
on rock or on a stiff sub-soil, becomes saturated with water till it | 
is in a viscous state and moves down the hillsides slowly ; an 
unusually heavy downpour of rain when it is in this condition, 
precipitates landslips down the hillsides, and considerable areas 
slide down, overwhelming the herbage which grew on them and 
that on the level ground at the bottom in one common destruction. 
A notable example of this kind was to be seen on the Illawarra 
Line near Clifton, when whole hillslopes moved down during the 
wet winters of 1889 and 1890. On the sides of Mounts Kembla 
and Keira too, the same occurred, but to a less extent. 
The late Professor Moseley has on this subject: ‘“Griesbach* in 
his account of the vegetation of Australia, dwells on the close 
relation of interdependence which exists between the tree vegeta- 
tion and the coating of grass which covers the earth beneath it, 
and remarks that the amount of light allowed by the trees to reach 
the ground beneath them is rendered more than usually great by 
the vertical position in which their leaves grow. Hence the 
growth of grass beneath is aided.”+ ‘It may be that this per- 
mitting of the growth of other plants beneath them and the conse- 
quent protection of the soil from losing its moisture, besides other 
1 
advantages to be derived, is the principal reason why, as is 
familiarly known, two widely different groups of Australian trees, 
viz., the Kucalypti and Acacias, have arrived at a vertical position 
of their leaves by two different methods.” After pointing out 
* Veg der Erde, p. 216. 
+ Notes of a Naturalist on the Challenger, p. 264. 
