468 MESSRS. J. PARK AND F. RFTLEY ON THE [Aug. 1 899, 



EXPLANATION OF PLATES XXXI-XXXIV. 



Plate XXXI. 



Geological Sketch-map of the Hauraki Goldfields, on the scale of 8 miles to 

 the inch. 



Plate XXXII. 



Fig. 1. II j^. Mercury Bay. — Obsidian banded by longulites and trichites. A 

 small brown spherulite is shown on the left of the field. X 18. 

 Ordinary light. (See p. 454.) 



2. H5. Mercury Bay. — Spherulitic and perlitic obsidian. The brown 



microfelsite-spherulites are, in places, quite spherical, in others poly- 

 gonal. In polarized light the dark crosses separate, in some cases as 

 in the interference-figures of biaxial crystals, in others the crosses 

 show irregular distortion as in the figure. X 18. Nicols crossed. 

 (See p. 454.) 



3. H,. Mercury Bay. — Portion of the preceding section, showing perlicity 



in the lower and large brown spherulites in the upper and left-hand 

 parts of the field. X 30. Ordinary light. (See p. 454.) 



4. II3. Omahu. — Spherulitic rhyolite, showing transverse sections of the 



arms of microfelsite-spherulites. X 30. Ordinary light. (See 

 p. 453.) 



5. H7 [109] Omahu. — Spherulitic rhyolite, showing transverse sections of 



the ariTiS of a microfelsile-spherulite, the dark isotropic borders 

 proving the superficial fusion of these bodies. Smaller spherulites 

 of the ordinary type and of a second generation occupy the spaces 

 between these arms. X 45. Nicols crossed. (See p. 455.) 



6. H- [109] Omahu. A brown microfelsite-spherulite, showing the body 



and portions of the arms. The spaces between the arras are minutely 

 spherulitic. These spherulites are of the ordinary kind, and have 

 been developed subsequently to the superficial fusion of the microfelsite- 

 spherulites. X 18. Nicols crossed. (See p. 455.) 



Plate XXXIII. 



Fig. 1. H- [109] Omahu. — That part of the drawing below the line mm 

 , represents a portion of one of the arras of a microfelsite-spherulite in 

 longitudinal section, and conveys a fair idea of the appearance of the 

 microfelsi tic matter. X 1100. Ordinary light. (See p. 456.) 



2. Diagrammatic I'epresentation of an isolated microfelsite-spherulite of 



the armed type. (See p. 456.) 



3. H,-. Waikino.— Perlicity in quartz of rhyolite. X 18. Ordinary light. 



(See p. 461.) 



4. II„. Waihi. — Fragments of brown glassy vesicular lava in chalcedony 



(' quartz-blow '). X 140. Ordinary light. (See p. 463.) 



5. IT3. Omahu. — Trichites composed of globulites, in rhyolite. X 250. 



Ordinary light. (See p. 453.) 



6. H^e- Waihi.— Crystallites in rhyolite. X 250. Ordinary light. (See 



p. 462.) 



7. H,(5. Waihi. — Portion of a crystal of biotite in biotite-rhyolite. X 30. 



Ordinary hght. (See p. 462.) 



8. Han- Waihi. — Glass-enclosures in a crystal of andesine, in andesite 



altered by solfataric action, x 30. Nicols crossed. (See p. 464.) 



Plate XXXIV. 



Fig. 1. Ilg [6] Omahu. — Spherulitic rhyolite, showing fluxion from secondary 



fusion around portion of an arm of a microfelsite spherulite which 



enters the field on the upper right edge. Part of a sraall nest of tridy- 



/ / mite is shown on the lower right edge of the field. X 140. Ordinary 



■./ light. (See p. 455.) 



2. 11^3 [187] Adit-level, Waihi. — Isotropic felspars in a fragment included 

 in rhyolite. The structuTe of the latter is partly spherulitic, partly 

 axiolitic. The felspars in the fragment are reduced to the condition 



