570 THE GEOLOGY OF THE WARRUMBUNGLE MOUNTAINS, 



tereticornis var. dealbata^ and E. coriacea [?]) forests, with oaks 

 {Gasuarina Cunninghamii, G. Luehman^ii) and belar (C. Gam- 

 hagei) along the banks of creeks. In the arfvedsonite-trachyte 

 .region the soil is still poor, but somewhat better than in the 

 sandstone country; pine trees are here typically absent. The 

 dark trachytes and trachyphonolites have fair red soils, and are 

 timbered with gums, ironbarks (chiefly Eucalyptus siderophloia), 

 wattles, pine {Callitris robicsta), emu-bush [Eremophila sp.), 

 Styphelia sp., etc. The trachydolerites and basalts are surrounded 

 by good red and black soils, commonly timbered with box {Euca- 

 lyptus hemiphloia var. alhens) and a fair sprinkling of kurrajong 

 (Sterculia diver sifolia). Outside the mountain region we have 

 the extremely poor and thirsty sandy soils of the Pilliga Scrub 

 to the north, thickly timbered with pine {Callitris calcarata); 

 and the vast black soil plains lying to the west and south-west. 

 Interspersed with the black soil plains there are belts of wretched 

 Sandy soil of the Pilliga type. In some of the valleys in the 

 mountains, as at Tundebrine and around Tooraweanah, where 

 basaltic detritus accumulates, and where wash from basic trachytes 

 is deposited, there are miniature black soil plains, in reality 

 occupying the position of alluvial fans. From the close resem- 

 blance of the black soil in these valleys to that of the plains, in 

 colour, touch, mode of cracking when dry, and vegetation it seems 

 very likely that the black soil plains owe their richness to detritus 

 brought down from the AVarrumbungle Mountains in the course 

 of ages. The black soil of the plains contains deposits of coarse 

 gravels and waterworn pebbles made up partly of volcanic rock 

 of the Warrumbungle type, and partly of quartz derived from 

 the breaking up of the conglomerates. These coarse materials 

 must have been carried down at a time when the rainfall was 

 greater in the mountains than at present. 



Wind-action is an important factor in redistribution in these 

 areas, but as the winds here are mostly westerly, they have not 

 taken any part in bringing down the detritus which formed the 

 black soil plains. The wind, however, is an important distributor 

 of pests. Almost every year produces a new variety of thistle, 



