270 KKCOHDS OK THE AUSTRALIAN MUSEUM. 



cm. It is associated in the hand specimen with crystals 

 of smoky and ordinaiy quartz, albite in Carlsbad twins, 

 and small scales of black mica, the last where the idiomorphic 

 felspar and quartz become merged into a fine-grained granite. 

 The basal plane is fairly bright, while x is corroded and quite 

 devoid of lustre, the distinction between the two being obvious at 

 a glance. 



Another specimen from this locality is in all respects similar to 

 the (much larger) group from Oban figured in PI. lii. The simi- 

 larity is so pronounced that one would almost be inclined to 

 regard them as fragments from one and the same block. 



Bolivia. 



(Plate xlviii., fig. 5 ; PI. xli.x,, figs. 3, 4). 



Just as the prevalence of Baveno twins marks the Oban ortho- 

 clase, so tlae special feature of the Bolivia occurrence, so far as- 

 represented in the collection, is tlie excellence of the Carlsbad 

 twins. The crystals are in general fresher tlian those from Oban 

 and Uralla, this being perhaps due to their being obtained from 

 druses in the "acid" granite, not from pegmatite veins and 

 lenses. 



In PL xlix., fig. 3 is shown a group consisting of three Carlsbad 

 twins and a Manebach twin, accompanied by three crystals of 

 slightly smoky quai-tz ; the same Manebach twin is partially 

 idealised in PI. xlviii., fig. 5. Another fine ciystal twinned on 

 the Carlsbad law (PL xlix., fig. 4) is one of a group of four, and 

 measures about 3 x - X 1 cm. The prism faces are smooth and 

 bright, the terminal faces and the b pinacoid slightly striated 

 parallel to their intersection with the plane of the a pinacoid. 



Inverell. 

 (Plate xlviii., fig. 6). 



From a decomposed felspar-porphyry about fourteen to twenty 

 miles north-east from Inverell good examples of Carlsbad twins 

 are obtained, one of which is drawn and partly idealised. 

 The crystals are quite different in appearance from those 

 described above from other localities in the State, as, instead of 

 being white or buff in colour, they are brick-red. The figured 

 crystal measures about 2 x - X 1 cm. 



That I am able to present a plate of shaded drawings is 

 largely owing to the instructions and hints of my colleague, Mr. 

 A. R. McCulloch, to whom my best thanks are due. 



