^96 E. 0. Teale: 



The rock on the summit of the plateau is a typical banded rhyo- 

 .lite, the flow lines being very conspicuous. 



The detailed succession of igneous material building up the Wel- 

 lington ma«s has not been worked out, but there is a noteworthy 

 thickening in the vicinity of Lake Karng. In the southern bluff of 

 Wellington the thickness is not more than IjQUO feet, but in the 

 vicinity of the Lake it is more than double that amount. This is 

 piobably accounted for mainly by the presence of marked irregu- 

 larities of the Palaeozoic surface on which the volcanic beds were 

 laid down. 



It is perhaps strange that no undoubted vent or fissure by which 

 the volcanic material reached the surface, has yet been definitely 

 recognised, nor have any dykes, acid or basic, been noted in this 

 region. Considering the high melting point of rhyolite, its viscous 

 nature, the deep dissection of the rocks, and the wide extent of 

 the lava flows in tliis region, it is perhaps reaiiarkable that some 

 ■ channel by which it reaehed the surface has not yet been recognised. 



No undoubted intrusive quartz-porphyries have yet been noted 

 in this region. 



A fine section of the rhyolite, showing its relations to the basal 

 • conglomerates and over-lying sajidstones, is shown in the course of 

 the Wellington, just north of ShaAv's Gap, or one mile and three- 

 quarters in a straight line north-west from the Wellington Dolo- 

 drook junction. (Loc. 1.) Here the river has cut a tortuous canyon 

 for about half-a-mile through the rhyolite, forming pi-ecipitous cliffs, 

 showing tine columnar structure. (Photo. 4.) 



The remaining portion of the series, amounting to some thou- 

 sands of feet in thickness, consists largely of alternating beds of 

 conglomerate, passing into pebbly sandstone and normal gritty 

 sandstone, separated by beds o^ varying thickness, of purple shales 

 and mudstones, with, in places, interbedded sheets of altered basalt. 

 (Melaphyre of Howitt.) 



Fossils are rare throughout the series. The first obtained came 

 from' the sandstones of the Avon River, and were descril^ed by Sir 

 Frederick McCoy as Lepidodendron Australe. The writer has since 

 noted Lepidodendron at four localities in the Macallister basin. 

 'They are as follow : — 



( 1 ) Roadside cutting near Basin Flat. 



(2) Roadside cutting, Macallister R. — Target Cr. Junction. 



(3) Reid's Selection, near Barkly R. 



( 4 ) Near Glencairn (Mr. Sweetapple's). 



