IV 



purposed to continue the descriptions from time to time as materials 

 and opportunity permit. The paper first dealt with the dolerito 

 ("debase" of authors) of the Cataract Gorge, Launceston, the samples 

 of rock selected for slicing having been taken from the quarry near 

 the Cataract Bridge. The essential mineral components are a plagia- 

 clase felspar, augite, and a little iron oxide. The felspars are mostly 

 turned out on the albite plan, and belong to the labradorite-anorthite 

 group. The augite is a group of large, ill-defined crystals moulding 

 themselves, as it were, upon the felspars. With regard to the genetio 

 history of the rock, its microscopical structure shows that it cannot in 

 any sense of the word he described as a lava poared out at the surface 

 in ancient times and cooled under atmospheric conditions. The 

 crystallisation indicates its formation below the earth's surface. The 

 rock agrees thoroughly with what is called the intrusive type, interme- 

 diate between the plutonic rock masses and volcanic lavas emitted at 

 the surface. The Zeehan white rock (a vesicular basic lava — melaphyre) 

 varies in appearance according to the degree of decomposition, and to its 

 condition as an ancient ash or a tufl" or lava flow. The stone tested 

 wag obtained from the Silver Queen mine through Mr. W. F. Petterd, 

 who is quite satisfied that the rock embedded with the schists. The 

 reader of the paper described how they were led to include the ston* 

 among the glassy melaphyres. Melaphyre is regarded by English 

 petrologists as altered basalt, and in this sense the Zeehan stone is the 

 vesicular form of old basaltic eruptive material altered into vesicular 

 basalt — vesicular melaphyre. The microscopical characters teash ua 

 that it is an old lava, and Mr. Petterd has stated that he has been able 

 to satisfy himself that it is interbedded with the slates ; that in one 

 of the adits of the Oooah mine it can be distinctly seen lying between 

 the slates and following their stratification. Picrite from Mount 

 Horror was the next class of rocks considered. This is a small clas3 

 composed of the ferro-magnesian silicates, and containing little or no 

 felspar. These are the ultra-basic rocks. The most important mineral 

 is augite. The purple colour results from the presence of titanic acid. 

 Having given a full description of the nature and affinities of Mount 

 Horror picrite, the writer concluded that its structure is coarser thao 

 that of a dolerite, and by its constitution it is an augite-olivine felspar 

 rock. Its relations are evidently with the olvine-dolerites, and con- 

 nected with the ultra-basic rocks. The paper may serve to direct 

 attention to this instance of a picrite in Tasmania, and elicit the com- 

 munication of further occurrences. 



Hon. Adye Douglas (the President of the Legislative Council) moved 

 a vote of thanks to the Vice-President, speaking moat highly of Dr. 

 Agnew, with whom he had been friendly since 1840. 



His Honor the Chief Justice (Sir Lambert Dobson) seconded, and 

 included the gentlemen who had contributed the three papers. Accord- 

 ing to Mr. Johnston, Tasmania was the best country in the world for 

 babies and old men. We had no right to be alarmed at the report of 

 diphtheria that spread some time ago, and he was satisfied that Mr. 

 Johnston's paper would do Tasmania a great deal of good, for in Taa- 

 mania we were too apt to decry what we ought to praise and value — 

 our climate and situation. 



The resolution was passed with acclamation, and the meeting termi- 

 nated. 



