BY H. I. JENSEN. 869 



(e) Present Changes. — A vecent rejuvenation is noticeable in 

 some streams like Maule's Creek. This appears to be due to a 

 gradual disappearance of arid conditions. 



Volcanic activity has been long extinct, and there is no likeli- 

 hood of its recurrence for many periods. The mountains are 

 being base-levelled to the level of the western plains by the slow 

 process of arid erosion. It is worthy of mention that, in addition 

 to the other evidences of arid erosion already enumerated, many 

 peaks in the vicinity of Dripping Rock, near Bobbiwaa Creek, 

 display a very marked serrate topography. This characteristic 

 I have not noticed elsewhere, and it is very striking. 



5. Springs and Artesian Water. 



Like the Warrumbungles, the Nandewar Mountains have 

 many springs at high altitudes. Most of the important mountain 

 springs flowed without intermission throughout the great drought, 

 1896-1902, when the creeks were all dry. Mr. Ritter told me of 

 one spring near Pound Mountain which increased in strength 

 during the drought to such an extent that the water rose in a 

 fountain-like jet as thick as a man's arm. 



The creeks dwindle enormously in size on reaching the plains 

 west of the Nandewars. The reason of this phenomenon is that 

 the water is absorbed by the great thickness of sandy allu vials 

 which flank the Namoi for miles on either side. 



Though many mesas south and south-west of the Nandewars 

 are probably referable to the Trias- Jura, the sandstones underlying 

 the alluvials of the plains in this quarter are mainly Permo- 

 Carboniferous, hence the area is non-artesian. Some miles north 

 of Narrabri, however, that is north-west of the Nandewars, there 

 are sandstones which may belong to the Triassic intake beds of 

 the artesian system. 



6. Minerals of Economic Value. 



The Nandewar Mountains, like the Warrumbungles, abound 

 in veins of "potch" (poor opal) which occasionally contain specks 

 of precious opal. The indications of precious opal are, however, 



