390 Transactions. — Geology. 



Opal, Si, H, or Si H s . — The more valuable varieties are not known in 

 New Zealand, but the inferior qualities are of common occurrence. 



Hyalite is mentioned by Dr. v. Haast as occurring in small masses, 

 lining cavities in the volcanic rocks of Snowy Peak and the Malvern Hills 

 (Jurors' Eep. N.Z. Ex., 1865, p, 256), and again in a few localities in the 

 volcanic rocks of Banks Peninsula (Trans. N.Z. Inst., vol. xi., p. 511), and 

 is also mentioned by Professor Liversidge (Trans. N.Z. Inst., vol. x., p. 496) 

 lining cavities in the vesicular grey trachytes of Bell Hill, Dunedin. 



Common Opal and Semi-opal are mentioned by Dr. v. Haast (Jurors' 

 Eep. N.Z. Ex., 1865, p. 256) as filling small cavities in the quartz por- 

 phyries of the Malvern Hills and Mt. Somers, and last year I obtained from 

 the drift of Owharoa a specimen which is of a pure milky- white colour. 



Wood Opal {Silicified Wood) is very common where siliceous rocks are 

 decomposing as at Petrifying Gully, Mount Somers. It is mentioned by 

 Dr. v. Hochstetter (New Zealand 1863, Eng. ed., p. 96) in the tuffs and 

 conglomerates of Ooromandel, and by Dr. Haast (Juror's Eep. N.Z. Ex., 

 1865, p. 256) from many localities in Canterbury. 



Pitch Opal. — A specimen from Dunstan is described by Prof. Liversidge 

 (Trans. N.Z. Inst., vol. x., p. 496) as follows : — " Brown, variegated, light 

 and dark shades. Hardness about 6. When heated in closed tube gives 

 off water, blackens, and emits empyreumatic odour ; the condensed water 

 has an acid reaction, and on evaporation leaves a carbonaceous residue 

 which blackens on ignition ; breaks with a well-marked conchoidal frac- 

 ture ; contains iron." There are two specimens of this mineral in the 

 collection of the Colonial Museum — one from the Harper Hills, and the 

 other from the Eakaia Gorge. 



Opal-jasper. — There is in the collection of the Colonial Museum a speci- 

 men of opaline quartz with jasper, from the trachyte tufa of Portobello, 

 Otago, which forms a very pretty ornamental stone. The predominating 

 colours as described by Prof. Liversidge (Trans. N.Z. Inst., vol. x., p. 496) 

 are red-brown, blue-grey, and opal-white. 



Siliceous Sinter. — Deposits of this class are found surrounding several of 

 the thermal springs, and have been well described by Dr. v. Hochstetter 

 (New Zealand, 1863, Eng. ed., pp. 398, 412). He says, in speaking of the 

 siliceous deposits of Orakeikorako : " The sediment of this, like all the 

 surrounding streams, is siliceous ; the recent sediment is soft as gelatine, 

 gradually hardening into a triturable mass, sandy to the touch, and finally 

 forming, by the layers deposited one above the other, a solid mass of rock 

 of very variable description at different places both as to colour and struc- 

 ture. Here it is a radiated fibrous or stalk} 7 mass of light brown colour ; 

 there a chalcedony hard as steel, or a grey flint ; at other places the deposit 



