THE NATUHE AND ORIGIN OF GILGAI COUNTRY. 337 



THE NATURE AND ORIGIN OP GILGAI COUNTRY 



(With Notes on Quaternary Climate). 



By H. I. Jensen, d.sc. 



[Bead before the Royal Society of N. S. Wales, December 6, 1911.^\ 



I. Nature of Gilgais. 

 Gilgai country is remarkably uneven country, consisting 

 of alternate hummocks and hollows. It occurs in its 

 characteristic form only on the western side of the Dividing 

 Range. Gilgai country has a similar appearance to the 

 ' melonhole ' country of the coastal swamps and the 4 crab- 

 holey ' country of the tablelands, but the irregularity of 

 the surface is much greater than these types. Sometimes 

 in the western country we get the terms * melonhole ' and 

 'crabhole' applied to the gilgai areas in which the irregu- 

 larity of the surface amounts only to a difference of two 

 or three feet between the tops of the hummocks to the 

 bottoms of the depressions. The genuine 'gilgai ' country 

 is much rougher. The differences in elevation between 

 the knolls and the hollows amount to ten, fifteen and even 

 twenty feet. 



The hummocks are sometimes of rounded outline, but 

 more often they are irregular in shape, usually serpentine, 

 vermiform or variously ramified. The depressions have 

 also correspondingly irregular shapes. The depths of the 

 hollows maybe very variable within a comparatively small 

 area. For some time after rain they contain stagnant 

 water. The angle of slope from the summit of a knoll to 

 the bottom of the adjacent depression may be anything 

 from 10° to 60°. In typical brigalow gilgai country a sec- 

 tion of the surface would consist of a very wavy line, the 

 crests from 25 to 50 feet apart, and the hollows 10 to 20 



V— Dec. 6, 1911. 



