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Between the Barrier Range and the Darling River there are tracts of sand-hills and 
undulating sandy country which have been well grassed (the term is comparative) and 
clothed with vegetation. The vegetation being eaten out, the soil would drift, particularly 
in seasons of drought. In other words, much of the trans-Darling country is in a state 
of unstable equilibrium. 
The consensus of evidence shows that the sand moves more than it used to do. 
What prevented this? Simply the vegetation, sparse though it was, which through a 
long course of ages had tended to knit it together. In fact, in sandy country, all that 
binds it together is vegetation. 
I presume that the drift sand is the product of the denudation or of the disin- 
tegration of the Desert Sandstone, but the origin is probably 'well known to geologists, 
who have chemical and other, data in regard to it. At all events, it is not rich in the 
elements which go to promote plant life. 
However, the actual origin of the sand appears to be a mystery. Mr. H. Y. L. 
Brown, Government Geologist of South Australia, attributes the origin of much of 
it to the action of artesian water. 
5. Causes of drifting sands. 
To summarise in some degree, three causes have resulted in drifting sands : 
(a) Droughts. 
Some authorities even aver that sands did not, in the old days, drift except in 
draughts. This is not correct, but they are more mobile now. 
In the Western country, much depends on the infrequent rains, especially upon 
the times at which they fall. Rain at a critical period will secure the germination and 
development of certain plants; if rain be withheld, a particular kind of plant will die 
out, at least for a period, in spite of a fall of rain at some other period of the year. 
It is assumed that each plant has a critical period on which its development depends, 
and the appearance of countless millions of, say, thistles at one time over a given area, 
and the disappearance of the same for a term of years, is attributed to the timely 
combination of rain and genial warmth in the one case and in their absence in the other. 
In Western plantings much depends upon this fortuitous rainfall. If it comes, the 
success of the venture may be assured ; if it be withheld, its success is problematical. 
It is this element of uncertainty which obtrudes itself into Western operations that 
renders dealing with this part of the country so very difficult. 
(b) Overstocking. 
It is very easy to criticise the pastoralist for overstocking, but there are so many 
variables to be considered in obtaining the constant as regards the carrying capacity in 
a particular year, that most of the overstocking is unavoidable, the result of our 
ignorance of the sequence of the seasons. The mechanical action of a flock of sheep, 
irrespective of overstocking, is important. They pulverise the soil, and for many 
years, and in dry times, the position of a flock of sheep has been readily detected in 
the distance by an attendant cloud of dust. 
