86 
G.—SANDHILLS. 
The last features of importance are the sandhills, 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 N.E. and S.W., due to the prevalence 
of S.E. 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 more 
clayey character than the material of the sandhills. They have one steep fall 
inclined at an angle of about 30° and situated on the side opposite to the quarter 
from which the wind blows, the other side having a gentler slope. 
The sandhills rise to very varying heights, 30ft. or 40{t. being a very common 
height, while in some-cases they reach 70ft., or even in some extreme cases 10(ft. 
above the level of intervening flats. The highest sandhills 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 sandhills, which are clothed over very large areas with 
“‘ porcupine grass’’ (Tvriodia). 
