200 REV. J. MILNE CURRAN. 



broken tesselated pavement. These plates are quite separate one 

 from the other, and yet, under crossed nicols, they all extinguish 

 together. It is evidently a crystal that has been corroded through, 

 or one hindered in its complete development by taking up too 

 great an amount of unsolidified magma. The latter I believe is 

 the true explanation of this remarkable structure. There is also 

 in this slice a twin plagioclase near a porphyritic augite on that 

 part of the slice next the numbered label, that extinguishes on 

 either side of the composition plane at angles of 33° and 34° nearly. 

 The crystal is therefore cut close to the zone OP : oo P oo, and the 

 mean angle would point to the felspar being oligoclase. 



Slice 9. — Porphyritic Basalt, German's Hill, Mount Canoblas, 

 New South Wales. The same exceedingly fine base characterizes 

 this slide. Under a one-fifth objective, it resolves itself into a 

 structure resembling the New England basalts in miniature. 

 Grains of magnetite, not visible with an inch objective are clearly 

 made out. Some minute but wholly idiomorphic augites with 

 magnetite grouped in lines along their outer boundaries are visible 

 and there is very little olivine. A green secondary product stains 

 the felspars. As the latter seem water-clear and fresh, this 

 €olouring material is probably derived from some ferro-magnesian 

 constituents that have now disappeared. Under high powers 

 plates of a light substance are detected filling cleanly cut joints 

 in the porphyritic oligoclase. The surface of this substance is 

 marked with minute figures, reminding one of the microlites in 

 the Arran pitchstones. In polarized light, very good examples 

 of polysynthetic twining form brilliant pictures. On the end of 

 the slice furthest from the numbered label, there is a group of 

 augites with devitrified glass and magnetite inclusions. One of 

 the augites is twined. 



Slice 10. — Porphyritic Basalt, north slope of Mt. Canoblas, 

 half-a-mile south of last specimen. This slice shows to advantage 

 under a two inch objective, the character of the base being just 

 resolved and the relations of the porphyritic plagioclases being 

 clearly defined. A few steam vesicles on the slice are seen filled 



