860 THE GEOLOGY OF THE NANDEWAK MOUNTAINS, 



the mountains stood higher and liad a greater rainfall. Abrupt 

 sandstone cliffs facing the S.W., and situated where Bibbla 

 Creek and Deriah Creek leave the mountains, are seen from 

 Tarriaro. This portion of the country is marked on the Govern- 

 ment Geological Map of New South Wales as Triassic. 



Black Mountain is shown on the Government Geological Map 

 as consisting of acid igneous rock. On my map (Plate xlvii.) I 

 have taken this for granted, although in ascending the mountain 

 from the south I saw only sandstones and conglomerates with a 

 basalt sheet on top. I saw, however, some loose fragments of a 

 dioritic rock, which must be derived from an outcrop near by. 



All the mountains between Black Mountain and Deriah 

 present the same features, and consist probably of sandstones, 

 conglomerates and shales of Upper Coal Measure and Trias-Jura 

 formations with basalt sheets on top. 



About IJ miles south of Maule's Creek, near Laird's place 

 (Berrioye Station); there is a ridge of hills running N.W.-S.E. 

 (Long Plain Mountain). It consists of conglomerate made up 

 chiefly of rhyolite pebbles. Mr. Laird has found fossil leaves in 

 ironstones associated with these conglomerates, and his description 

 of them answers to that of Glossopteris, so that the conglomerate 

 must be Permo-Carboniferous, and the rhyolites from which the 

 pebbles in them are derived must therefore be older. The 

 pebbles of Maule's Creek consist of rhyolite chiefly, with a little 

 granite, basalt and trachyte. In Horse-Arm Creek the pebbles are 

 mostly of basalt, sandstone and trachyte. 



The average height of the hills (mesas) north and south of 

 Maule's Creek in this region (^'.e., between Horse-Arm Creek, 

 Pinnacle Creek, and Stony Creek, Berrioye Station) is 1,400 feet, 

 increasing towards the north and diminishing towards the S.W. 

 At Buron Creek conglomerates of Permo-Carboniferous age are 

 observed dipping N.W. On the Coolah side of this creek the 

 valley of Maule's Creek becomes a gorge with high hills fronted 

 with cliffs and escarpments on both sides, while down stream 

 Maule's Creek flows in a broad valley — a perfect plain continuous 

 with the Tarriaro and JSJarrabri plains — and delimited on the 



