MAY, 1899. 



The monthly meeting of the Royal 

 Society of Tasmania was held on Tuesday, 

 May 16, at the Museum. The President, 

 the Administrator of the Government 

 (His Excellency Mr Justice Dodds, C.M.G., 

 C.J.) presided. 



THE PRESIDENT CONGRATULATED. 



The Hon. C. H. Grant, M.L.C, on behalf 

 of the Council of the Royal Society, heartily 

 congratulated the Administrator upon the 

 distinction which had been conferred on 

 him, and which reflected honour upon the 

 Society of which he had been so long a 

 Fellow, and was now, as Acting-Governor, 

 officially the President. He trusted the 

 Administrator would live many years to 

 enjoy his dignity as Chief Justice, upon 

 which he shed honour and lustre. (Ap- 

 plause.) 



The Hon. Adye Douglas, President 

 of the Legislative Council, said they 

 all congratulated the Administrator on 

 the honour to which he had acceded, 

 and he, as an old col®nist, had a special 

 pleasure in offering him his cordial felici- 

 tations. (Applause.) 



His Excellency the Administrator of 

 the Government, in returning thanks, 

 said he had been taken by surprise by 

 the kind utterances, for which he grate- 

 fully thanked them. They were rendered 

 to him all the more pleasing as they 

 came from two gentlemen with whom in 

 years gone by he had been associated in 

 Parliament— especially Mr. Douglas, at one 

 time his colleague and chief, and whose 

 character he respected now as then. 



NEW MEMBERS. 



The following members were elected: — 

 Miss M. Davis, A.C.P., Hon. W.W. Perkins, 

 M.L.C, Messrs. H. Nicholls, LL.B., W. 

 Middleton, C.E., A. C. Parker, Eustace 

 Maxwell, Dudley AUport, Chas. Harrold, 

 A. E. Risby, and the Rev. W. H. Webster. 



VISITORS. 



The Secretary (Mr. Alex. Morton) intro- 

 duced tlie following visitor : — Mr. H. M. 

 Chrisp, engineer of the Great "Western 

 Railway. 



ROCKS AT MOUNT READ. 



The Secretary submitted the following 

 paper on "Felsites and Associated Rocks 

 of Mount Read," by Messrs. W. H. Twelve- 

 trees, F.G.S., and W. F. Petterd, 

 O.M.Z.S. :- 



Associated with the schists on the slopes 

 of Mount Read and Mount Black are some 

 obscure igneous rocks, usually silicious 

 and often slightly schistose. These are 

 what are called in the field by geologists 



"felstones" or "felsites." The tei-ul 

 felsite carries ditt'erent meanings in 

 ditterent. countries. In Germany it is ap- 

 plied to the compact groundmass of quartz 

 porphyries, which are the acid volcanics of 

 pre-tertiary age. In England it designates 

 the rock itself, not its groundmass merely. 

 Unfortunately, the English use has come 

 to include acid effusive rocks and acid 

 intrusives under the same term. Thus 

 elvan dykes are sometimes called felsites, 

 and divitrifled sheets of rhyolite are called 

 by the same name. The authors explain 

 their use of the names they apply to the 

 Mount Read rocks. They confine the 

 terms felsite and quartz felsite to divitri- 

 fled acid lavas, and apply the term 

 " quartz-keratophyre " to the same rocks 

 when containing an alkali-felspar rich in 

 soda. The Mount Read rocks, marked by 

 great geological age and distorted and 

 miner;! logically reconstructed by intense 

 dynamic metamorphism, are not easy to 

 deciplier ; and their felsitic nature 

 is often obscured by green colouration 

 due to free development of chlorite. 

 Occurring in the schist zone, they have 

 been aff'ected by the forces which produced 

 the foliation of the schists, and often have 

 a streaked, rolled-out flinty aspect. Their 

 speciflc gravity ranges from 2"6 to ^"74. 

 The rock is very prevalent on the north 

 side of Mount Read, is met with at Rose- 

 bery and the Red Hills, and at other 

 points in a line having a N. and S. direc- ■ 

 tion for about 20 miles. It was probably 

 geologically contemporaneous with the 

 schists. Whenever the felsite appears in 

 tunnels driven through the metalliferous 

 phyllites or schists, ore ceases to be found. 

 Being an intercalated sheet it cut off the 

 ore. The ore bodies on Mount Read form 

 lenticular masses in the argillitic schists, 

 parallel with the plane of foliation. There 

 is no reason to suppose that cavities 

 exisited in these foliated beds in readiness 

 for filling up with mineral. The parting 

 planes of the schists were most likely the 

 first channels for inetal-bearing solutions, 

 and the process of chemical replacement 

 probably started from these channels, 

 removing the country rock on either side 

 and leaving ore in its place. The ore bodies 

 come in and die out in these channels, and 

 will probably be found to be quite as 

 persistent in their repeated occurrence as 

 the flexures to which the sedimentary 

 rocks have been subjected. To obtain some 

 knowledge of the true nature of the slates 

 and schists, samples of each were chemi- 

 cally treated, with the result that argillite 

 or argillaceous schist seems the most 

 appropriate name for the least altered 

 varieties. Other descriptions are phyllites 

 or clay slates lustrous with mica ; 

 tale ^schists, silicious schists, micaceous^ 



