OCCURBENCE OF TINGUAITE AT KOSCIUSKO, N.S.W. 381 



Tertiary or Upper Oretaceous. It would appear to be more than 

 an accident that the chronological relations of the chief nepheline 

 and younger soda-rocks to the Tertiary basalts are so similar 

 throughout Australasia, for example, in Queensland near Port 

 Mackay and at the Glass House Mountains; in New South Wales 

 at the Warrumbungle Mountains, the Oanoblas, the Gib Rock and 

 Barigan; in Victoria at Mount Macedon; and in Tasmania at 

 Port Cygnet, the nepheline and other younger soda-rocks appear 

 in every case to be a little older than the "older Tertiary" basaltic 

 lavas. It may be mentioned also that at Kerguelen Island the 

 phonolites are thought to be a little older than the basalts, the 

 latter being considered to belong to some part of the Tertiary Era, 

 perhaps to the Miocene. It has occurred to us that there is 

 possibly a fine field for research in studying the distribution of 

 soda-bearing rocks (such as these nepheline rocks of Kosciusko), 

 in relation to areas of subsidence, elevation, or stable equilibrium. 

 So far it would appear that the extrusion of such soda rocks in 

 Australasia has taken place chiefly along the edges of great sub- 

 sidence areas. 



It would appear then that in Australasia magmas rich in soda 

 have risen chiefly from the septa of folds in the earth's crust rather 

 than from the tops of ge-anticlines or from the deep seated por- 

 tions of geo-synclines. The latter in Australasia have mostly 

 yielded either basic or ultra-basic lavas or massive hypabyssal 

 dykes, sheets, or bosses of diabase, while the former (the ge-anti- 

 clines) have produced acidic rocks such as granites and rhyolites. 

 At the same time the fact should not be lost sight of that even 

 the basic dyke rocks which have risen from beneath the centre of 

 the geo-syncline under Sydney contain a good deal of soda, primary 

 analcime being present in some of these dykes. 



We are specially indebted to Mr. G. W. Card, a.r.s.m., f.g.s., 

 for the kind help and advice he has given us of which we have freely 

 availed ourselves. We are also indebted to him for the Miigge 

 and Brogger diagrams. Our thanks are also due to Mr. W. S. 

 Dun, f.l.s., for assistance in studying the bibliography of the 



