204 REV. J. MILNE CURRAN. 



good examples can be collected both in situ and from tuffs and 

 agglomerates. The porphyritic basalt referred to, is an older and 

 more acidic rock than the ordinary basalt. In these basalt flows 

 we have the records of probably the most extensive Tertiary 

 volcano in New South Wales, as traces of its activity can be 

 noticed over nine hundred square miles of the country around. 

 The rich gold bearing drifts of the Forest Reefs, Lumpy Swamp, 

 and Lucknow, were buried under these basalts. Many interesting 

 relics of an extinct vegetation have also been discovered beneath 

 the lavas that flowed down from the Canoblas.* 



Slice 14. — Basalt from twenty miles north of Armidale, New 

 South Wales. To the unaided eye, the felspars and magnetite 

 are visible in this slide. Under the microscope, in ordinary light, 

 the rock shows well shaped plagioclases together with augite and 

 olivine, set in confused masses in an almost opaque base. The 

 average length of the plagioclases may be put down at the one- 

 eightieth of an inch. In the thinest parts of the slide, the opaque 

 base is made out to be a devitrined glass, thickly set with mag- 

 netite dust. The large masses of augite next demand atten- 

 tion. This mineral is seen pierced by the lath-shaped felspars, 

 giving rise to an ophitic structure. Olivine is also present, being 

 recognizable, under crossed nicols, and also in plane light, by its 

 ground glass appearance. The opacity of the ground mass and 

 the water clear character of the felspars give this rock a very 

 interesting appearance under the microscope. 



Slice 17. — Basalt from Vegetable Creek, New England. In 

 hand specimens this shows as a compact dark-bluish rock. Few, 

 if any, of the constituents are visible to the unaided eye. It 

 weathers to a dull grey, coloured with patches of red. Under 

 the microscope in common light, micro-porphyritic felspars 

 are developed. The longest of these felspars goes up to one- 

 fiftieth of an inch ; their average may be put down as one- 



* Mueller, Observations on New Vegetable Fossils of the Auriferous 

 Drifts, Decade L, p. 27, Ibid, Decade II., p. 5 ; Ann. Report Dept. of 

 Mines, New South Wales, 1875, p. 125. 



