m- W. S-. BENSON. 277 



about 40 miles is preserved of the gravels of an old stream 

 which may be termed the Nandewar River. Several former 

 tributaries, other than those ah-eady mentioned, are also in- 

 dicated. At Tea Tree Creek, ten miles S.S.E. of Barraba, a 

 thickness of 160 feet of basalt overlies 80 feet of gravel. From 

 here, an air-gap leads straight through the low hills to Barraba, 

 where, on the School-house Hill, is a small capping of Tertiary 

 drift. These may have been connected by a stream, the "Anti- 

 Manilla,"' as suggested in Text-fig. 10. The drifts, which under- 

 lie the Mt Elijah basalts, eight miles south of Barraba, may 

 represent a tributary of this hypothetical stream. Probably, 

 also, there was another stream which ran parallel to the present 

 Borah Creek, but about a couple of miles to the north of it, the 

 " Proto-Borah Creek " ^See p.279j. In addition, the basalt- 

 capped drift near Hawkin's Creek, and that near the junction of 

 Upper Manilla River with Little Creek, may indicate the former 

 presence of pre-basaltic streams where are now the valleys of 

 Upper Hawkin's Creek and the Upper Manilla River. In the 

 latter are several low hills capped with Tertiary drift. 



The phenomena of gravel-filled Tertiary valleys covered by 

 basalts are, of course, universal throughout Eastern Australia, 

 and no explanation of this particular valley-system would be 

 necessary other than that put forward by Mr. Andrews, namely, 

 that it was aggraded in a period of depression, which occurred 

 during the general movement of uplift(40), were it not for certain 

 special features. The elevations cited show that the slope of 

 the valley was reversed, and that the basalt-lava must have 

 flowed along the valleys in the opposite direction to that of the 

 flow of the pre-existing streams. The suggestion, that the 

 tilting of the land-surface towards the east was connected with 

 the outbreak of volcanic activity in the Nandewar Mountains, 

 is supported by the abundance of volcanic tuff, sanidine-crystals 

 and pumice occurring with the diatomaceous earth below the 

 basalts, where a small lake was formed by the ponding-back of 

 the stream in its valley, thus tilted. This easterly tilting, com- 

 bined with the elevation of the Nandewar Range with respect 

 to the present plains to the south and north, determined the 



