136 Transactions. 



paratively free from inclusions, and without any traces of 

 secondary iron-ore dust, so that resorption of the amphibole in 

 this zone did not take place. The outer zone of the spherule 

 consists of a delicate fern-like growth of micropegmatite. The 

 change from crypto- to micro-pegmatitic structure is gradual 

 from the centre of the spherule to the circumference. The 

 branching of the outward creeping fern-like growths did not 

 generally occur until two or three fifths of the radius of the 

 spherule had been attained. Optically the spherules extinguish 

 in sectors as the stage or the nicols are revolved ; in some the 

 sectors are narrow, in others considerable areas are extinguished 

 at the same time. (Plate XVIII, fig. 4, and Plate XVII, figs. 2. 

 and 3.) . 



The sections of the rocks described have been compared with 

 sections of rocks from the most notable alkaline petrol ogical 

 provinces of the world — viz., the Arkansas rocks, described 

 by Williams ; the Christiania rocks, described in Brogger's 

 famous memoir ; and the rocks of the Serro do Tingua, in 

 Brazil, described by Hussack. For the loan of slides of these 

 collections, and for his ready assistance and advice, I am deeply 

 indebted to Dr. P. Marshall, of the Otago University 



EXPLANATION|OF|PLATES?XYII-XIX. 



Plate XVII. 



Fig. 1. A gabbro-diabase boulder. The rounded water-worn appearance 

 is due to spheroidal weathering. A part of the shell-like 

 concentric weathered easing can be seen adhering to the stone 

 beneath the right-hand end. Eight-mile Creek Diggings. 



Fig. 2. (No. 19.) Grain of quartz enclosed in spherule ; ragged crystals 

 of riebeckite surrounding periphery of spherule. 



Fig. 3. (No. 19.) Showing fern-like growths in outer part of spherules 

 and sectors of spherules. 



Plate XVIII. 



Fig. 4. (No. 19.) Riebeckite in granite-porphyry. 



Fig. 5. (No. 28.) Lamprophyre approaching monchiquite. 



Fig. G. (No. 32.) Tinguaite-porphyry, showing large crystal of nepheline. 



Fig. 7. (No. 34.) Tinguaite, containing aegerine-hornblende-augite, nephe- 

 line, cancrinite, perthite, and anorthoolase. 



Fig. 8. (No. 72.) Tinguaite, containing segerine, nepheline, cancrinite, 

 and anorthoelase. with some resorbed amphibole. 



Plate XIX. 



Kg. 9. (No. 119.) Theralite. Large twinned schulerized crystal of eegerine 



occupies tlie left-hand half of figure; the balance is labrador- 

 itc, hornblende, nepheline and augite with iron-ores. 



Fig. 10. (No. 115.) Microperthite in aplite. 



Pig. 11. (No. 107.) Tinguaite showing junction of normal rock with leu- 

 cocratic patch. 



