TEANSACTIONS OF SECTION C. 143 



13. From Base of Cliffs of White Decomposed Bock heticecn 

 Porphyry Dykes, Portohello Pwmontory. 



Rock. — Light greyish-green, dense and tough, not porphy- 

 ritic. Gives much gelatinous sihca on treatment with HCl. 



Sections. — Clear, though in parts slightly hazy, ground-mass 

 of allotriomorphic nepheline, densely intermixed with long- 

 acicular green microlites (aegirine?), and rather sparingly with 

 microlites of sanidine. There occur, however, small irregular 

 patches of the nepheline ground-mass nearly free of the green 

 microlites. Idiomorphic nephelines small and not numerous. 

 Sanidines very scarce, and those occurring form mostly Carls- 

 bad twins. Augite thinly scattered in generally small 

 columnar crystals of green colour, which are more or less 

 strongly impregnated with dust and grains of iron -ore. 

 Apatite scarce. Iron-ore in small grains very sparingly dis- 

 tributed throughout the ground-mass. Water-clear, sharp 

 angular particles of glass tolerably frequent. 



14. Quarry at Logan's Point, Duneclin Harbour. 



Bock. — Greenish-grey, dense and compact, not porphyritic. 

 Gives much gelatinous silica on treatment with HCl. 



Sections. — The microscopic character of the rock has been 

 described by Professor Hutton, of Christchurch ;''■' but I have 

 here to mention that, in addition to the component minerals 

 he describes (plagioclase, augite, &c.), I found in my sections 

 unmistakable small idiomorphic nephelines and sanidines, 

 some in Carlsbad twins, wdiilst the large amount of gelatinous 

 silica afforded on treatment of the powdered rock with HCl 

 indicates that a large percentage of the ground-mass consists of 

 allotriomorphic nepheline. 



15. North- East Valley, near Normanhy, about Two Miles 

 north-east of Duneclin. 



Bock. — Dark greenish-grey, dense and porphyritic, some of 

 the larger porphyritic inclusions being recognisable by the 

 naked eye as feldspar and nepheline. 



Sections. — Clear ground-mass of allotriomorphic nepheline, 

 densely filled with greenish microlites (aegirine?), and more 

 sparingly with microlites of sanidine. The greenish microlites 

 and dusty matter are in patches so much accumulated as to pro- 

 duce a greyish haziness, imparting to the ground-mass a mottled 

 light and grey appearance. Sometimes only narrow, irregular- 

 veinlike, lighter portions are left between much larger darkened 



* The Eruptive Rocks of New Zealand : Trans. Roy. Soc. New South 

 Wales, 1889, p. 134. 



