254 PROCEEDINGS OF SECTION C. 



True nepheline phonolites, tephrites, leucitites, &c., have not been 

 met with so far in these districts. Nor have any true hypabyssal or 

 plutonic equivalents of the alkaline lavas been found. Many of the 

 lavas are, however, so like hypabyssal rocks in fabric and appear- 

 ance that if described by a petrologist unacquainted with the region 

 they would be given the names distinctive of the hypabyssal group. 

 Many of the comendites would be termed paisanite. 



Bare Miiierals. — A number of rare minerals characteristic of 

 alkaline rocks have been detected and described in my papers dealing 

 with special regions. 



In addition to riebeckite, arfvedsonite, eegirite, zirconite, micro- 

 perthite, and anorthoclase, which are common constituents, wohlerite, 

 eucolite (?), nosean, analcite, meliphanite (?), guarinite (?), cossyrite, 

 and barkevicite have each been detected in some of the rocks which I 

 have described. Because of these rare minerals our alkaline rocks pre- 

 sent an interesting and puzzling study to the petrologist. 



From the correlation of chemical analyses with microscopic work 

 it is clear that the peculiar structure, composition, and texture of the 

 alkaline rocks are largely due to the action of pneumatolytic vapours 

 carrying HF, HCl, Ti02, and Zr02 i^ the period of consolidation. 



5. Petrology. — In order that the mineralogical composition of 

 the principal of these rocks may be clearly understood, the following 

 abridged petrological descriptions are given : — 



(a) Ortliophyric Pantellarite. — Mount Ngun-Ngun, Glass House 



Mountains. 



Texture: Holociystalline, poi'phjTitic, orthophyric, with 

 microcrystalline to cryptocrystalline base. 



Constituents : Sanidine, anorthoclase, arfvedsonite, 

 riebeckite, cossyrite, chalcedony, and quartz. 



Analysis : 



S,0„ ... 72-38 CO, ... n.d. 



AhO, ... 12 21 TiO, ... 0-25 



Fe,0, ... 8-36 ZrO, ... n.d. 



Feb ... 0-69 P„0. ... trace 



MgO ... 017 Ci ' ... 001 



CaO ... OlS MnO ... 0-70 



Na„0 ... 3-52 NiO ... 004 



K,6 ... 5-20 



CH„0(KKr)+ (0 86 Total ... 100-26 



lH,O(100°-) io-69 



Magmatic Name : Liparose. 



(b) Orthophyric Come?idite.^M.ount Conowrin, Glass House 



Mountains. 



Texture: Holocrystalline, microcrystalline, orthophyric. 



Constituents : Sanidine, anorthoclase, riebeckite, quartz 

 (micrographic intergrowth with felspar). 



