TRANSACTIOKS OF SECTION C. 149 



particle, is shown the end of an augite crystal, so densely filled with 

 magnetite grains that its green colour appears only in small specks ; and 

 this is also the case with several smaller crystals and grains of this 

 mineral, distributed with those of hornblende through the section — one 

 (a), close to centre of lower edge, appearing nearly black-opaque. Near to 

 this dark crystal is a group of grains of olivine (o), transparent, with a 

 slightly greenish tint, seemingly representing a large grain broken up. 

 Each grain has a strong black margin of iron-ore, and around the whole 

 group runs a broader margin of densely-aggregated small grains and dust 

 of this ore, and the crevices between them are filled with it. The larger 

 grains are slightly serpentinised along the cracks. The ground-mass is 

 colourless-transparent, and consists, as in the Pine Hill rock, of allotrio- 

 morphic nepheline and microlites of sanidine ; but, with the exception of 

 the portion below the hornblende crystal, it is more densely filled with 

 greenish microlites and dust and grains of iron-ore, whence results a 

 darker-speckled aspect. 



Fig. 5. — On the left-hand edge, near the upper part of figure, are two 

 large ill-formed sanidines (.s) — a long thin columnar one overlapped by a 

 shorter and broader one, of which only part is seen. Below this are two 

 prismatic crystals of brown hornblende (/;), lying parallel to each other 

 and both nearly free of grains of iron-ore. The hexagonal section {h) 

 further to the right is also a crystal of brown hornblende, cut at right 

 angles to the vertical axis, its outlines representing the traces of the 

 clinopinacoid and prism. It is quite free of grains of iron-ore, but its two 

 lower sides have strong black ferruginous margins. On the right-hand 

 edge, in line with this crystal, is another large sanidine (s), slightly dimmed 

 by inclusions along its lower edge. Attached to this edge is an unusually 

 small square section of nepheline (n). A much larger section of nephe- 

 line, dimmed by dusty matter, is seen low down near the left-hand edge of 

 figure. The bright, irregularly-outlined grain marked (g) near the centre of 

 the figure is water-clear glass ; and along the lower edge is shown part of a 

 large prismatic crystal of green augite, much cracked and having a narrow 

 .zone of fine grains and dust of iron-ore along the margin. The appearance 

 and constitution of the base is similar to that of Pig. 4. Some of the larger 

 prismatic microcrystals are brown hornblende, some green augite, and 

 the larger black grains arc, from their contours, no doubt magnetite. 



Fig. 6. — This is drawn in ordinary light from a thin slide of the riDck 

 •of the Purakanui cliffs. Magnified 26 diams. 



The large, irregularly-outlined grain (g) is water-clear perfectly 

 isotropic glass, exhibiting under a high magnifying power a multitude of 

 larger and smaller vapour-cavities, mostly arranged in strings. Close to 

 its right-hand edge, near bottom margin of figure, is a very small hexa- 

 gonal section of nepheline (n). There are three small prismatic crystals, 

 marked (a), in upper part of figure, of which the two dark ones on the left 

 were once green augite, but are now nearly changed into dusty black 

 iron-ore, only fine specks of green colour denoting their former character; 

 the third and smallest one is still green augite throughout. The ground- 

 mass, consisting of allotriomorphic nepheline, is colourless-transparent, 

 and its peculiar appearance in variously-outlined figures of lighter and 

 darker shade is due to a weaker and denser accumulation of tufts and 

 groups of greenish microlites. Solid grains of iron-ore are sparingly dis- 

 tributed, but dusty iron-ore renders portions of the base quite dim and 

 black-opaque, as at the upper right-hand corner of the large glass-grain 

 and near the small crystal of nepheline. 



Fig. 7. — This shows the outlines of three colourless transparent glass 

 particles drawn from same slide as Fig. 6. JIagnified 15 diams. 



The large centre one is especially interesting, as resembling a long 

 prismatic crystal broken and fractured at one end. The irregularly-out- 

 lined small portions marked with crosses along its right-hand and upper 



