352 H. I. JENSEN. 



mingling with pine along them instead of the usual associ- 

 ation of pine and box. That this arid period has come 

 to a close is evidenced by the deep U-shaped depressions or 

 gullies cut by the present creeks from the Warrumbungies 

 in the deep late Tertiary alluvial. Thus at Baradine, the 

 creek is a deep gully 40 feet below the surrounding level 

 country. The banks of the creek rise steeply, indicating 

 that this gully has been carved and is being enlarged by 

 each successive flood. The same is the case with Bohena 

 or Borah Greek and other creeks until they get 20 or 30 

 miles away from the mountains. Along their lower courses 

 in the plain country these creeks still occupy depressions, 

 more shallow courses carved by the rare and occasional 

 big floods, and filled up again with sand by smaller floods. 

 The smaller creeks in this plain country do not actually 

 occupy depressions. Their beds are lower than their banks 

 but about the same level as the country passed over. The 

 banks are built up of sand washed down from the hills ; 

 is the product of the period of arid erosion redistributed by 

 water in the present cycle. 



This is the case in the gilgai belt where small creeks like 

 Oakey Hole Greek and Brigalow Greek are entrenched 

 between banks of their own flood products. The fact that 

 streams carrying down sheets of sand have been able to 

 sweep over the gilgai plain indicates a restoration of 

 integrated drainage by the advent of moister conditions. 



(c) The Castlereagh and Coonamble Plains. — At Ooo- 

 namble and on the surrouuding plains we also get abundant 

 evidence of an arid period having existed prior to the 

 present period. The deep alluvial soils are underlain by 

 great thicknesses of sandy drift and clays deposited over 

 the Coonamble district area in the wet periods of Tertiary 

 time. The lake or swamp in which this alluviation took 

 place dried up on the inauguration of arid conditiens, but 



