346 Albert V. James : 



It might be thought that the Lower Series belongs to the Older 

 Basalt, but there is strong evidence against this: — 



(1) The Lower Series rests in places on thick deposits of sand, 



which appear to be the normal Kainozoic grits. 



(2) The river conglomerates between the two series frequently 



contain basalt pebbles derived from the lower series. 

 These pebbles are only slightly decomposed. If they were 

 older basaltic they would be thoroughly decomposed. 



(3) Older 'basalt, three miles to the E.S.E., is thoroughly de- 



composed, while the lower series deijcribed above is only 

 slightly weathered. 



Scoria Cone. — Near the junction of Column Gully and Jackson's 

 Creek is a scoria cone which was almost submerged by the youngest 

 lava flows. A study of the\ sections shows that at first effusive and 

 explosive eruptions alternated, and then gave place to a prolonged 

 discharge of scoria and agglomerate. The uppermost of the four 

 layers of scoria is still about 100 feet thick. Probably denudation 

 has reduced its thickness. At one point a wall of dense basalt 

 pierces the scoria. It is evidently a blocked up vent, or dyke. 



The scoria is of the same age as the *' Organ Pipes," and the 

 eclumns in Column Cully, and, therefore, belongs to the Lower 

 Series of Newer Basalt. At one point on Jackson's Creek scoria 

 overlies and underlies the columnar basalt. 



Microscopic Examination of Upper Newer Basalt. — Sections were 

 made of very tough basalt from the small quarry on Deep Creek, 

 north of the Leaf Beds. It proved to be a hypocrystalline rock, in 

 which some glass was present. Large plieniocrysts of olivine were 

 set in matrix of fairly coarse labradorite. Augite and magnetite 

 were very abundant, while iddingsite frequently replaced the 

 olivine. The sections gave good examples of ophitic structure, for 

 augite commonly included the labradorite laths. Flow structure 

 was illustrated by the orientation of the labradorites, and the man- 

 ner in which they ** flowed" round the olivines.' The rock was a 

 coarse grained basalt. 



Porphyritic Basalt. — In the triangle between Redstone Hill, 

 Bulla and the Organ Pipes, there is a peculiar flow of dense por- 

 phyritic basalt that belongs to the Upper Series. Near the Red- 

 stone Hill, a volcano on Jackson's Creek, it is found resting directly 

 on the sands that separate it from the Lower Series. In several 

 places in Deep Creek and Jackson's Creek it is found in a perfectly 

 fresh state, but above the Organ Pipes it appears in a more 

 weathered and vesiculai- state. Boulders of this porphyritic basalt 



