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, 

 lliese peljbles 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- 



comjDosed, while the lower series described above is only 

 slightly weathered. 



Scoria Cone. — Near the junction (if 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 efiusive 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. Proljably denudation 

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

 pierces the scoria. It is evidently a. l>locked up vent, or dyke. 



The scoria is of the same age as the " Organ Pijies," and the 

 columns in Column Gully, and, thei"efore, belongs to tlie Lower 

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

 overlies and underlies the columnar basalt. 



Microscopic Examinatioii of U pper Xeirtr 73axalf. — 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. Lai-ge phenocrysts of olivine were 

 i^et in matrix of fairly coarse labradorite. Augite and magnetite 

 were very abundant, while iddingsite frequently replaced the 

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

 augite commonly included the labradorite laths. Flow structure 

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

 ner in which they " floAved " round the olivines. The rock was a 

 eoarse grained basalt. 



Porphyritic Basalt. — In the triangle between Redstone Hill, 

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

 phyritic Ijasalt that belongs to the Uppe\- 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 vesicular state. Boulders of this porphyritic basalt 



