18 
(c) Nature of the Course and Channel of the Finke.—As one might expect, 
judging from the figures just given, the course of the Finke from the Mac- 
donnell Ranges to the southern slope of the James Range is not so sinuous as 
it is after it debouches upon the Cretaceous plains. On these plains its course 
be omes extremely meandering, the river making its way down the very gentle 
incline from these ranges to Lake Eyre only after performing numerous sweep- 
ing curves. The width of its channel varies considerably, being usually 
narrower and deeper in the ranges, but widening out as it leaves them. On 
emerging on to the plains it becomes flatter and shallower and dotted with gum 
trees, which are not confined to the banks only as in the ranges, but grow often 
in patches even in the middle of the channel. 
(d) Absence of Surface Running Water.—The absolute dependence of the 
presence of running water in the bed of the Finke upon direct supplies of rain 
has its explanation in the following facts :— 
(1) The basin of the Finke, although of great extent, is entirely confined, or 
nearly so, to an area over which the climatic conditions are the same. 
(2) Rain falls usually only at certain seasons, there being long intervals of 
drought. 
(3) There is an almost total absence of springs at the head of the Finke and 
its tributaries, and in the few instances of their occurrence the dis- 
charge 1s very small. 
The influence of these three factors on the absence of surface running waier 
is obvious. After the floodwaters caused by a heavy downpour have subsided, 
and during the long intervals of dry weather, surface running water is absent 
from the greater length of the channel, its appearance for short distances only 
at certain parts being due purely to local causes. The absence or paucity of 
springs is to be attributed to the absence of a sufficiently thick layer of soil on 
the mountain slopes to act as a reservoir by absorbing the rain water and giving 
it out gradually at lower levels in the form of springs. It is also due to the 
absence of joints in the Pre-Cambrian and their scarcity even in the Ordovician 
rocks. The rain waters are, therefore, not absorbed, but form torrents, and 
rush down the bare mountain slopes into the valleys. When the waters have 
reached the beds of the watercourses, their rapid absorption by the porous strata 
and the excessive amount of evaporation that is always taking place cause the 
almost total disappearance of surface water from the river channels. 
(e) Waterholes.—At certain seasons of the year, should the fall of rain be 
sufficiently great, the supply of water in the channels of the rivers exceeds the 
amount that can be absorbed by their sandy beds, and this produces a flow of 
water down the channel. This is often spoken of locally as a flood, as the 
waters as a rule are not confined to the channel by the low river banks, but 
spread out over the wide alluvial flats which border the main channel. 
When rain ceases to fall the flow of water diminishes almost immediately in 
volume. This it continues to do until running water disappears from the 
surface over an ever-increasing length of its course. There are, however, for 
a month or two after a heavy rainfall portions of the channel over which 
running water may still be seen; but these gradually decrease in length until 
the channel assumes what may be termed its normal state. In this state the 
channel is occupied by long stretches of white sand devoid of surface water, 
