460 MESSRS. J. PARK AND P. RTJTLEY ON THE [Aug. 1 899, 



are so diminutive that it is difficult to speak with certainty upon this 

 point. Under an amplification of 250 diameters the spherulites are 

 seen to consist of irregularly branching fibres. In some cases 

 margarites seem to be present, but there are so many globulites in 

 the spherulitic aggregates that it is not easy to say how far they 

 may assume any definite order. These spherulites and axiolites are 

 nearly isotropic, only a faint hazy light being transmitted when 

 they are viewed between crossed nicols, even when care is taken to 

 exclude all extraneous light. Apparently they are microfelsite- 

 spherulites. 



The section contains some porphyritic crystals, which, from their 

 outlines, may safely be regarded as having once been felspars. 

 There are also fragments of such crystals, but in all cases they have 

 undergone alteration by fusion and may be considered as felspar- 

 glass. In most instances they are perfectly isotropic, but a few 

 show very feeble traces of double refraction, and two or three of the 

 smaller fragments possess a microcrystalline structure. (PI. XXXIY, 

 fig. 2.) 



The evidence seems, on the whole, to show that the rock has been 

 reheated, at all events to a sufficient extent to fuse the felspars. 

 The lithoidal character of the rock is probably due to a later 

 globulitic devitrification. The dark specks visible in the hand- 

 specimen are seen under the microscope, in reflected light, to be 

 crystals and irregularly-shaped patches of pyrites. 



II^^[191]. Grand Junction Mine, 100-foot level, Waihi. 

 — This is a pale greyish-white or yellowish lithoidal rock, showing 

 numerous minute colourless crystals with glassy lustre. 



Under the microscope the rock is seen to be a rhyolite with 

 a poorly-defined, irregularly-corrugated fluxion -structure. The 

 lithoidal character of the rock is mainly due to globulitic devitrifi- 

 cation. The section contains numerous small aggregates of tridymite, 

 and many porphyritic crystals and fragments of crystals of felspar, 

 which are for the most part oligoclase and andesine, but some are 

 sanidine ; also an occasional crystal of labradorite may be seen in 

 this section. Some of these crystals and fragments are more or less 

 corroded, but most of them are so cat that measurement of their 

 extinction-angles afl'ords only an approximate clue to the nature of 

 the felspars. Crystals and specks of pyrites and magnetite are 

 present ; also a few small fragments of other rocks, apparently 

 rhyoiitic. An analysis made by Mr. Philip Holland is tabulated 

 on p. 467. 



Hj5- Waikino. — A pale bluish-grey rock with grains of quartz, 

 some little dark crystals, small ochreous specks, and infiltrations of 

 bluish-white opal. 



Under the microscope the rock appears to consist, apart from the 

 numerous porphyritic crystals which it contains, of almost completely 

 isotropic matter, and in this appear in places, when the section 

 is examined in ordinary transmitted light, markings which indicate 



