THE NATURE AND ORIGIN OF GILGAI COUNTRY. 347 



15 to 20 miles south of Brigalow Greek on the back runs of 

 old 'Cubbo' station. These mudsprings are described as 

 mound springs. One is described as being situated in the 

 centre of a round clay pan. The bushmen believe that 

 these clay pans are often formed by the subsidence of 

 country round the vent of a mudspring. Clay pans with a 

 saline soil, studded with extinct mounds built up by mud- 

 springs are reported as numerous in the comparatively 

 unknown parts southward from Brigalow Creek. It has 

 been suggested to me by local men that the gilgais are the 

 result of mudspring action, but while I can readily under- 

 stand that round mounds and circular depressions can be 

 formed in this way, I fail to see how the labyrinthine courses 

 of the gilgai contours can be formed in this way. 



Having now disposed of the various theories advanced 

 by others, I desire, before advancing my own to discuss a 

 question which bears considerably on the result. It is that 

 of Late Tertiary Climate. 



VI. Late Tertiary Climate. 



In several papers 1 I have given facts in evidence of 

 remarkable changes of climate in our western districts in 

 Late Tertiary and Quaternary times. It is generally 

 agreed by geologists that in the late Tertiary periods large 

 areas of Central Australia consisted of lakes receiving 

 sediments from the high ranges that separated these parts 

 from the coast. Central New South Wales and Queensland 

 constituted a depression in which extensive alluviation took 

 place. Mammalian drift occurs in places and gives evidence 

 in favour of a moist, if not very wet, climate. The remark- 

 able fauna of giant marsupials which existed up to the end 



1 Prelim. Note on the Geol. History of the Warrumbungle Mountains, 

 Proc. Linn. Soc. of N.S.W., May, 1906. Geology of the Warrumbungle 

 Mountains, loc. cit., August, 1907. Geology of the Nandwar Mountains, 

 loc. cit., 1907. 



