1883. | The Geology of Central Australia. 1133 
the direction of the wind the sandhills also vary. The drifting 
sand has been arrested in its course by the bushes and other veg- 
etation, and thus the sandhills have been gradually built up, al- 
though they have often been cut away and re-deposited, thus 
giving rise to the irregular position of their layers. Such is the 
general surface formation of the sandhill country, but here and 
there among the parallel ridges are solitary crescent-shaped sand- 
hills whose long axes are at right angles to the prevailing system 
of hills. Facing the concave side of this variety of sandhills 
there is always a clay flat, at the other end of which the parallel 
sandhills re-commence, as seen in the sketch. 
In the above sketch the concavity of the sandhill B-B is shown 
facing to the north; quite as often, however, they face to the 
south. The clay flat is always opposite to the concave side. 
These sandhills are usually several miles apart. What their ori- 
gin is I cannot say. They possess the same structure as the 
normally built ones. It is possible that they may be the remains 
of another system of sandhills which by an alteration of climate 
Producing a great change in the general direction of the prevail- 
ing winds, have been swept away and a new system formed. But 
if this is the case, why the crescent shape and why the variation 
of position among them? They have certainly not been formed 
by water, nor has their shape been modified to any great extent 
by its action, for if that was the case some traces would be left. 
And besides they are generally situated among the sandhills far 
away from any watercourse. There must be some cause for their 
existence. What that cause is I must admit is a mystery to me. 
I think the subject worth investigation, for it is certainly remark- 
able that there should be these anomalous cases scattered here 
and there through a region unique for its uniformity. 
In the north-western portion of the basin, where the Cretaceous 
beds of kaolin occupy the surface, denudation has worn the soft 
clays into a great variety of fantastic shapes. Minarets, castles, 
temples and even grotesque images of man and beast are repli- 
cated on every hand in the greatest variety of dazzling colors. 
These are every shade from jet-black to snow-white. Gorgeous 
Purple, delicate pink, rase red and somber brown, green and blue 
are mingled together with amazing confusion and prodigality. It 
'Sa riot—a mad dance—a very carmagnole of color. It wom 
seem as if same mischievous elves had been rioting in nature's 
