-96 ' E. 0. Teaie: 



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

 Jite, the flow lines being very conspicuous. 



The detailed succession of igneous material building up the Wel- 

 lington mass 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 IjOOO feet, but in the 

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

 probably 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 vient 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 this region, it is perhaps remarkable that some 

 channel by which it reached 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 sandstones, is shown in the course of 

 the Wellington, just north of Shaw'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 precipitous cliffs, 

 showing fine 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 off varying thickness, of purple shales 

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

 (Melaphyre o.f Howitt.) 



Fossils are rare throughout the series. The first obtained came 



fromi the sandstones of the Avon River, and were described 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). 



