183 
(c) The rabbit pest. 
This is the real cause of overstocking, and it is. involuntary on the part of the 
pastoralist. This pest has become acute during the past thirty years, and has accentuated 
any overstocking by sheep. 
6. Prevailing Winds. 
Mr. Russell told me that the prevailing winds in the Western country, capable of 
piling sand, vary from north-west to south-east. According to the preponderance and 
strength of these winds, so will the direction of the sand-ridges vary. It will, of course, 
be borne in mind that the direction- of the ridges will be at right angles to the prevailing 
wind. 
Mr. A. W. Howitt is of opinion that the strongest winds in the Lake Eyre district 
of South Australia are south-west. 
According to the late Mr. R. Helms, the prevailing direction of sand-dunes is 
east and west, and they are rarely more than half a mile apart. 
See a valuable paper by Colin J. McMaster, Chief Commissioner of Western 
Lands,* where the author points out that the sand-dust is travelling eastward : 
That the imperceptible eastward trend of the sands has not been specially marked in the past is not 
sufficient ground for assuming that an equally slow rate of progress will take place in the future, because, 
up to within recent years, the land was more or less covered with vegetation ; but now, to an alarming 
extent, vegetable growth of all kinds has disappeared, and in the future the sands may drift in every dry 
season, instead of during periods of prolonged and excessive drought, such as this State has recently passed 
through. 
This paper contains also interesting sections of levels across sand-hills shifting 
north-easterly under the influence of south-westerly drought winds, County of Lands- 
borough, Western Division, New South Wales. 
The last features of importance are the sand-hills, which occupy the surface over immense areas of 
the interior. These are ridges of usually a red, argillaceous sand, having in many localities an approximately 
parallel arrangement, and therefore with a constant trend, usually north-east and south-west, due to the 
prevalence of south-east winds, but elsewhere occurring quite irregularly. The trend of the sandhills is to 
a great degree dependent upon the direction of the prevailing wind, being almost at right angles to this. 
Separating the ridges are the corresponding diminutive valleys, the floor of which is usually of a much moro 
clayey character than the material of the sand-hills. They have one steep fall, inclined at an angle of about 
30 degrees, and situated on the side opposite to the quarter from which the wind blows, the other side having 
a gentler slope. 
The sand-hills rise to very varying heights, 30 or 40 feet being a very common height, while in some 
Cases they reach 70 feet, or even in some extreme cases 100 feet above the level of intervening flats. The 
highest sand-hills were crossed during the trip from George Gill Range to Ayers Rock, where also the greatest 
development of them was seen. The surface of almost the whole of this strip of country is occupied by 
sand-hills, which are clothed over very large areas with " porcupine grass " (Triodia). (Report, Horn 
Scientific Expedition to Central Australia. March, 1896. Part III Geology and Botany.) 
Proc. Roy. Soc. X.S.W., Vol. xxxvii, 138 (1903). 
