494 MS. E. EUTLEY ON [Aug. I9OO, 



Porphyritic crystals and fragments of felspar also occur. These, 

 from their extinction-angles, may, in some cases, be referred to 

 sanidine, in others to andesine. The section also contains small 

 crystals and grains of magnetite and some limonite, the latter 

 probably pseudomorphous after pyrites, llmenite may likewise be 

 present in small quantity, but the evidence upon this point is un- 

 satisfactory. 



H 22 . Waihi. — The specimen shows conchoidal fracture, and is 

 scratched with difficulty by a knife-blade. It is dark brown, and has 

 a resinous lustre, but there are paler spots and markings upon which 

 the resinous lustre is absent. The rock has the general appearance 

 of ordinary semi-opal. 



Under the microscope, in ordinary transmitted light, the section 

 varies from nearly colourless to pale yellow, and in places is almost 

 orange-yellow, with deep brown spots which sometimes are sur- 

 rounded by annular borders of like colour but slightly separated 

 from the nuclear spots. Only parts of the section appear to be 

 isotropic when viewed between crossed nicols, a considerable portion 

 of it being traversed by irregularly-reticulating, anisotropic streaks, 

 which vaguely suggest the possibility of an original vegetable 

 structure. 



Since the label, forwarded with the specimen, states that it 

 occurred in rhyolite, it may possibly have been a fragment of 

 silicified wood, 1 taken up and more or less altered by a lava- 

 stream. Dr. G. J. Hinde, F.R.S., to whom I submitted the section, 

 kindly examined it and, while reserving any definite opinion upon 

 it, favoured me with a letter, from which the following statements 

 are extracted : — 



* I feel much doubt whether any wood structure is now shown in it. Whether 

 it may have been wood originally, and has had the structure destroyed, is 

 another question ; but considering the very perfect preservation of the structure 

 in fossilized wood, I do not think that such has been the case with this specimen.' 



He further adds, 



' I do not see how wood is likely to have been preserved if caught up and 

 enveloped in a recent condition by a lava-flow; it might possibly not be 

 destroyed if it were at the time silicified.' 



H 23 . Water -race, Waihi. — A pale pinkish-grey rock, contain- 

 ing dark-grey angular fragments, ranging from almost microscopic 

 dimensions to more than an inch in diameter. 



The rock is seen under the microscope to be a pumiceous 

 r hy oli te-t Tiff containing crystals of plagioclastic felspars, mostly 

 oligoclase and andesine. Quartz and biotite are present in small 

 quantity. The section shows one fragment of quartz which has 

 been cracked into three pieces. They have been slightly separated, 

 and the middle one somewhat displaced, so that it has a different 

 orientation from that of the two terminal portions. A fragment of 



1 In Hochstetter's ' New Zealand ' (1863) transl. E. Sauter (Stuttgart, 1867), 

 it is stated on p. 119 that silicified wood occurs 'in the creeks in many 

 localities where siliceous rocks are decomposing.' 



