CxX. IRRIGATION GEOLOGICALLY CONSIDERED. 
mud flowing from the mound springs, as in Queensland, 
records as high as from 120° ahr. have been obtained, as 
for instance at Mount Browne on the Lower Flinders. As 
the mean surface temperature of that locality is consider- 
ably lower than this, it is obvious that the liquid mud in — 
such cases must come from some depth. This consideration 
taken in conjunction with the fact already stated that flow 
from artesian bores dries the mud springs in the vicinity 
proves that the source of the springs is to be found in the 
artesian wells water-bearing strata. The mud springs are 
in fact natural artesian wells, where the water under 
pressure from the storage beds below forces its way to the | 
surface through the overlying clayey beds, where they are 
thinnest, and therefore offer least resistance. As might 
be expected, these conditions are found near the margins 
of the basin in proximity to the older rocks, for there the 
upper beds of the artesian series which are usually imper- 
vious clays become more sandy and therefore more porous, 
in accordance with the well known rule that sediments 
become coarser the nearer they are to the parent rocks 
from which they have been derived. 
Desert Sandstone.—This formation, to which reference 
has already been made, is of Upper Cretaceous age, and 
extends as far south as Bidura near Balranald. North- 
wards it extends into Queensland, westwards into South 
Australia, and south-eastwards it extends up to or even 
considerably beyond the limits of the artesian basin. It 
does not follow therefore, that the formations underlying 
Desert Sandstone areas always belong to the artesian series, 
as in many cases the Desert Sandstone rests immediately 
upon the older rocks. Owing to the great denudation 
which this formation has undergone, it does not extend 
continuously over the areas just described, but occurs as 
isolated and generally low hills or ranges. These in New 
