HORN KXPKDITION — PHYSICAL (irOOKAFIIY. 25 



G.— SANDHILLS. 



Tlie ];ist fpatui'fs of importanrn aj-e ilw sainlliills, wliicli (XMupy tlic surface 

 over ininiense areas oi tlie interior. Tliese are ridges of usually a icd argillaceous 

 sand, liaving in many localities an approximately parallel arrangement, and there- 

 fore with a constant trend usually N.E and S.^^^, due to the pre\alence of S.E. 

 wind.s, 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 I'idges are the cori'esponding 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 ^•arying heights, thirty or forty feet being a very 

 couHiion height, while in .some cases they reach seventy feet, or even in some 

 extreme cases 100 feet al)ove the level of intervening flats. The highest sandhills 

 were crossed during the trip from George Gill llange to Ayers Hock, where also 

 the greatest development of them was seen. The surface of almost the whole of this 

 strip of country is occujiied by sandhills, which are clothed o\er \ cry large areas 

 with "porcupine gi'ass" {Triodu}). 



