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abate over these portions, there usually remain a string of waterholes occupying 
the depressions in the river bed. It rain does not fall for some time these one 
after another lose their water by evaporation and become dry. Only those 
which occupy the deepest and most sheltered depressions hold out for any length 
of time. Such waterholes prevail in the Cretaceous area as in the Stevenson, 
Macumba, and Coglin Rivers, and form the chief sources of supply in the 
districts where they occur. 
What a valuable provision of nature in reality are the sandy beds of the rivers ! 
Through the sand and gravel the water creeps slowly down its course protected 
to a great extent from evaporation, and here it may generally be obtained by 
sinking; whereas if it had remained on the surface it would have been rapidly 
evaporated. Only in those places where ledges of rock cross the channel do the 
waters appear at the surface, and then usually for a short distance only, dis- 
appearing again in the sand on the other side of the rocky bars. 
Seldom do the floodwaters of the Finke and Macumba flow over the surface 
to Lake Eyre; for the lacustrine delta of these rivers, consisting for the greater 
part of deposits of sand and loam which have been accumulating during the 
Late-Tertiary and Post-Tertiary epochs absorb the immense body of water 
brought down by these rivers. 
(f) Rainfall m its Relation to Surface Water. —The rainfall throughout the 
area of the Finke Basin is somewhat variable, ranging from an average of less 
than din. per year in the central and southern portions to 10in. or 12in. over 
much of the mountainous country in the northern part of the basin. The mean 
annual rainfall throughout the basin cannot be more than 6in. to 7in. 
A great part of the moisture that falls as rain throughout this area is lost by 
evaporation. From claypans and all shallow depressions which expose large 
surfaces to the desiccating agents, the water disappears in two or three months 
after a fall of rain. From the waterholes, too, during the dry season, the 
water disappears at an alarming rate. Waterholes which have been examined 
by one explorer during a good season, and declared to be permanent, have, when 
examined later by a second explorer in a rather dry season, been often found to 
be dry, or nearly so. Explorers have indeed been rather too hasty in forming 
conclusions as to the permanency of waterholes, which visited perhaps during a 
good season, contained a good supply of water, but which had in reality no 
element of permanency. In the great majority of cases they are not fed by 
springs nor situated in places sufficiently sheltered to give practical permanency 
to them. 
Besides the great quantity of water directly evaporated, some of it goes to 
supply the wants of the gums which line the banks of the creeks. In times of 
heavy flood some of the water may reach Lake Eyre along the channel of the 
Macumba, while a Jarge portion filters gradually down towards Lake Eyre 
through the bed of the creek at a moderate depth from the surface. Lastly, 
an important portion of the rainfall percolates through the outcrops of the 
porous strata of Cretaceous age, travels downwards towards Lake Eyre, and 
forms the supply from which the artesian water is derived. Some of this water 
reaches the surface again in several localities by natural outlets, and issues from 
the mouths of mound springs. Some of the water probably percolates the sand 
and gravel of the river beds, and in this way reaches the water- bearing strata of 
he artesian basin. 
