OCCURRENCE OF TINGUAITE AT KOSCIUSKO, N.S.W. 347 



On the OCCURRENCE of a VARIETY of TINGUAITE 

 at KOSCIUSKO, N. S. WALES. 



By Prof. David, b a., f.g.s., f.r.s., F. B. Guthrie, f.i.c, f.c.s., 

 and W. G. Woolnough, b.Sc. f.g.s. 



[With Plates I., II.] 



[Bead before the Royal Society of N. S. Wales, June 5, 2.90/.] 



CONTENTS. 



I. Introduction. 



II. Occurrence at Kosciusko. 



III. Microscopic Character. 



IV. Chemical Composition. 



V. Relation to allied rocks. 



VI. Age. 



VII. Summary. 



I. Introduction.— The rock described in this paper was dis- 

 covered during a visit of two of the authors (Messrs. David and 

 Guthrie) in company with Mr. Richard Helms, to the Kosciusko 

 Plateau last February. Eruptive rocks, in which the felspathoid 

 mineral nepheline replaces felspar, are somewhat rare in their 

 distribution, and all the more interesting on that account. In 

 England for example, nepheline rock of the nature of phonolite 

 is known to occur only at the Wolf Rock, S.E. of the Land's 

 End, Cornwall. The Wolf Rock is a Nosean Phonolite. 1 



1 S. Airport, Geol. Mag. vin., 1871, 247, and i., 1874, 462; also F.Z., 

 Mikrosk. Besch. 1873, 397. "The Wolf Kock lies about nine miles S.E. of 

 the Land's End, and is covered by the sea at high water. At low water 

 spring tide it measures only 175 feet by 150 feet, and stands 17 feet above 

 the sea. At high water it is two feet below the level of the sea. It con- 

 sists of microporphyritic crystals of sanidine and nosean ; and the ground- 

 mass which is holocrystalline consists of sanidine nepheline and a few of 

 nosean and a^girine." British Petrography, with special reference to the 

 igneous rocks, by J. J. Harris Teall, m.a., f.g.s., p. 367. 



