^^^- 55-] KHY0LITE3 OF THE HlURlKI GOLDFIELBS. 453 



constitute the greater portion of the rock. Doubtless the former 

 as suggested by Vogelsang, have, after solidification, been again 

 partially fused, so that the surfaces and ends of the arms became 

 rounded. A spherulitic envelope was then formed around them, 

 and subsequently the small spherulites were developed. 



H3. Omahu. — This is a somewhat deep pinkish-grey rock, which, 

 on the cut surface, is seen to be traversed by a few buff-coluured 

 continuous bands, between which are small irregular markings of a 

 like pale colour. 



The microscope shows the rock to be composed of alternating 

 spherulitic and microcrystalline bands. The spherulites are of the 

 ordinary kind, having a radiating-fibrous structure, and giving the 

 usual dark cross between crossed nicols. In ordinary transmitted 

 light, however, the section shows two extremely interesting bands in 

 which more or less transverse sections of the arms of brownish sphe- 

 rulites of Rosenbusch's microfelsitic tj'pe are seen (PI. XXXII^ 

 fig. 4) ; these, between crossed nicols, become more or less dark. 

 They are not affected by the subsequent development of spherulites 

 of the ordinary radiating fibrous-crystalline type. The globulites by 

 which the larger and earlier-formed brownish spherulites are devi- 

 trified often form margarites and longulites, while trichites are also 

 present. The margarites, or rectilinear series of globulites, show a 

 general tendency to run in the direction of the branches or fingers 

 of the spherulite, but they not unfrequently cross one another. 

 These and the curvilinear trichites may distinctly be seen to consist 

 of lines of globulites w^hen magnified 250 diameters (PL XXXIII, 

 fig. 5). Hosenbusch makes a distinction between such curvilinear 

 globulitic forms and true trichites, although he admits that a 

 passage exists between them, consisting in a more or less longulitic 

 fusion of the globulites.^ 



The section contains numerous opaque octahedra which appear 

 black in reflected light : these are rarely more than ^t^ inch in 

 diameter. Small specks of a yellow colour and metallic lustre may 

 also be seen in reflected light. The black octahedra may be re- 

 garded as magnetite; the yellow specks are pyrites. Being in doubt 

 whether some of the latter might not be gold, I submitted a 

 sample of this specimen to Mr. Philip Holland, who kindly ex- 

 amined it by Skey's method and found that, although pyrites was 

 present, there was no trace of gold. 



H4. Mercury Bay. — A black glass with a very few white 

 spherulites. Judging from its general appearance, it seems to be an 

 ordinary obsidian. 



A section of this rock, when viewed under the microscope between 

 crossed nicols, appears to be completely isotropic, with the exception 

 of one or two brown spherulites, which have a radiating structure, 



^ ' Mikrosk. Physiogr. d. petrogr. wicbt. Mineral.' 3rd ed. vol. i (1892) p. 35. 



