556 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS. 



they are all contemporaneous and of Post- Carboniferous age; they 

 may even be as late as Tertiary. 



I might mention in this connection that the removal by denuda- 

 tion of a few hundred feet of sandstone in the district of the 

 Glass House Mountains, Queensland, would leave them standing 

 in the midst of rocks at least as old as Carboniferous. It is 

 likely therefore that many of the alkaline rocks of America now 

 associated only with Eopalseozoic or Archaean sediments may be 

 as late in age as the Glass House Mountains but on account of 

 higher relief have had their Mesozoic sediments denuded away. 



The only other alkaline rocks from the South American region 

 which I know of are the Tertiary(?) phonolites of the Little Island 

 of Trinidad,* Gough's Island, Ascension, St. Helena, and the 

 Island of Fernando Noronha.f 



South America therefore conforms to the plan which we have 

 already found to hold good elsewhere, viz., that alkaline rocks do 

 not occur in the folded ranges or in areas of great sedimentation, 

 but they are found on the faulted portions of plateaux or conti- 

 nental masses which have only been submerged at considerable 

 intervals, and then only for a brief period. 



Ch. iv. Australasia. 



From Possession Island, a relic of ancient Antarctica, aegirine 

 (nepheline 1) phonolites have been recorded by G. T. Prior J 



Kerguelen Island consists of numerous lava-flows of which the 

 oldest consists of trachyte and phonolite, the later of basalt. 



New Zealand. — Professor P. Marshall, of Dunedin, has 

 described a fine series of foyaitic rocks from the Province of 

 Otago.§ The back country of the Province of Otago is composed 

 of gneisses and schists. The volcanic area has undergone many 

 vicissitudes in the Tertiary epoch, and the eruptive rocks are, 

 according to Hutton's view, Post-Oligocene, according to the 



* G. T. Prior, Min. Mag. Vol.xii. 

 ' t G, T. Prior, Min. Mag. Vol.xi. 

 % Min. Mag. Vol. xii. 

 § " Geology of Dunedin," Q.J.G.S. Vol. lxii. 1906, pp.381-424. 



