68 



irregular in shape, and have an average diameter of 0'005 

 millimetre. 



On examining a freshly prepared slice, the contents of 

 many of these cells are seen to be in rapid motion, evidently 

 due to ebullition of the liquid contents caused by rapid dif- 

 fusion of its gas through cracks developed in preparation of 

 the section, or perhaps by diffusion through the wall of the 

 cell where sufficiently thin. In one case the commotion was 

 seen to be due to the dissolving up of a tiny black particle 

 (probably a hydrocarbon) in the liquid contents of the cell. 

 This particle was noticed to diminish to half its bulk in ten 

 minutes. In the case of two under examination all commo- 

 tion had ceased by the next day. 



The rock is apparently a variety of fine-grained pegma- 

 tite, having the composition of a granite aplite, probably 

 crystallized in the presence of abundant liquid gases. The 

 later stages of crystallization have been those favouring the 

 inclusion of the liquid gases, perhaps owing to rise of pres- 

 sure due to gas escape being cut off. 



The odour suggests that this gas may contain hydro- 

 gen sulphide, carbon bisulphide, acetylene, or like compounds. 

 As available material was limited, little could be done to- 

 wards definitely settling its nature. Chemical methods ren- 

 dered possible through the courtesy of Professor Rennie, 

 D.Sc, were undertaken. 



The rock was powdered in a large mortar, under ammo- 

 niacal water, containing a few drops of lead acetate. Only 

 the slightest browning was noted, indicating that hydrogen 

 sulphide could not be present in more than the minutest 

 quantities. The powder was then digested in hydrofluoric 

 and nitric acids, and sulphuric acid tested for, with no better 

 result. 



Further investigation has been suspended pending ar- 

 rival of additional supplies of the rock. 



Atacamttio from Bimbo wrie. 



Atacamite is extensively developed in the zone of 

 weathering at the Mt. Howden Copper Mine.-^' Though prac- 

 tically identical in chemical composition, three forms are to 

 be distinguished, differing greatly in physical appearance. 



The most striking is an arrangement of radiating lamel- 

 lae in bunched masses, often 5 centimetres in diameter, form- 

 ing magnificent specimens for exhibition purposes. When 

 well developed the lamellje measure 3'7 cms. by 2 cms., and 



* Mount Howden is situated on Bimbowrie Run, within sight of the 

 Barrier Ranges, and just *W miles in a direct line north of Olarw 



