THE NATURE AND ORIGIN OF GILGAI COUNTRY. 339 



aggraded portion of the western slopes and on the plains 

 adjoining the slopes. 



Mr. G. H. Halligan tells me that he has seen gilgai 

 country well developed between the Kalga Range and 

 Ooonamble (Urawilkie). 



The universal experience of scientific workers seems 

 therefore to show that gilgai country occurs at the base of 

 our western slopes in areas where aggradation has been 

 great and often in places where indications of late tertiary 

 subsidences are in evidence. It lies in the zone between 

 the areas of denudation and the great Black Soil Plains 

 and Red Soil Plains of the west. 



III. Characteristic Vegetation. 



The typical gilgai country of the Pilliga Scrub is covered 

 with dense brigalow and belar scrubs. The brigalow col- 

 lected was identified for me by Mr. J. H. Maiden as Acacia 

 harpophylla, and the belar as Casuarina lepidophloia. 

 These two timbers seldom grow intermixed, but in some 

 gilgai areas brigalow is wholly in possession, in others 

 belar. Occasionally on the edges of gilgai country, as near 

 Narrabri West, grey ircmbark (Eucalyptus erebra) may be 

 sparingly associated with the brigalow. Where such is the 

 case the inequalities of the surface are only slight, amount- 

 ing to two or three feet at the most. In other places the 

 poplar box (E. populifolia) is seen to extend some chains 

 into the gilgai, especially where belar holds sway. Wilga 

 (Geijera parviftora) occurs sparingly in both belar and 

 brigalow gilgais even in their centres, but especially where 

 there is a tendency to the formation of red soil on the sur- 

 face of the hummocks. On 4 crabholey' country near the 

 edges of gilgai areas, and also on larger blocks of ' crab- 

 holey' and 'melonholey' country, that is, less strongly 

 developed gilgai than the deep gilgai, an oak (Casuarina 



