356 H. I. JENSEN. 



This factor is the migration of salts and carbonates of lime 

 and magnesia into the hummocks by capillarity. Chemical 

 analysis shows the hummocks to contain a higher percen- 

 tage of these substances than the depressions. So great 

 has the precipitation of lime been in the hummocks, that 

 at a depth of six inches it forms little pea-shaped nodules 

 or concretions in the soil. Unquestionably the forces of 

 capillarity have in the present cycle done much to enlarge 

 the hummocks. Inequalities of surface must have pre- 

 existed and might have been produced by one or all of the 

 suggested causes, but the main features of gilgai country 

 as distinct from 'melon-hole' country is the augmentation 

 of existing inequalities of surface by capillary action. 



Mudsprings. — Some mudsprings are supposed to be still 

 active in remote portions of the Pilliga Scrub. Many 

 extinct ones occur, as well as salt pans formed by mud- 

 springs. These occupy a line along the border between 

 the flat alluvial belt of the north-western plains and the 

 outermost outcrops of Trias Jura formation. Not having 

 seen these mudsprings it is not possible to say anything 

 with confidence about them. Yet their presence along the 

 border between the belt of heavy Tertiary alluviation and 

 the Trias Jura suggests that they might have been produced 

 by the expulsion of enclosed water from the loosely cemented 

 Tertiary debris by the settling down of this material under 

 its own weight. The Tertiary gravels of the Pilliga Scrub 

 are very water bearing, though only pumping supplies are 

 obtained in the bores. 



The bearing of the here suggested origin of the mudsprings 



has an important bearing on the origin'of artesian water. 



The matter is of economic interest and wants further 



investigation. 



Villi Summary. 



In this paper I have given a description of gilgai country, 



some remarks on the distribution of such lands, and possible 



