liformly distributed 

 gathered into irregular masses, sometimes as curaulites but 

 more often with defined edges and transparent bands between the 

 pa,tches. Sometimes the base is pumiceous. In some places 

 microlites are numerous, in others they are few and scattered. 

 The porphyritic minerals are quartz, sanidine and plagioclase, with 

 a little brown hornblende and pale green augite in small fragments. 

 The plagioclase is subordinate to the sanidine. The felspar crystals 

 go up to -0 4 inch. Thomas, Report on the Eruption of Tarawera, 

 p. 16. 



Enstatite Rhyolite. 

 Lake Taupo—El&ck or dark grey rocks of different shades, often 

 banded or damascened and sometimes with a sub-vitreous lustre,, 

 occasionally vesicular ; shewing usually scattered crystals of glassy- 

 felspar. S.G. 2-35 to 2-40. Section : Ground-mass very abundant 

 partly crystallitic and partly miorolitic ; the crystallitic portions 

 globulitic and more or less opaque ; the microlitic portions more 

 or less transparent. The two textures are variously arranged, 

 sometimes in layers, but usually the more opaque portions form 

 clouds through the microlitic portion, not sharply defined but 

 shading one into the other. Sometimes the layers are very distinct 

 and parallel forming the Lithoidite of Hochstetter. The felspar 

 "^'"~"'"'" about -00.5 in length. Tht 



_ plagioclas 

 crystals, and perhaps a little augite. 1 found no quartz. The 

 felspar crystals are from -03 to -08 in length. The enstatite is in 

 prisms about -04 to -08 in length, and -01 to-04 in thickness, rarely 

 the length goes to -15. It is rather strongly pleochroic, a and ^ 

 reddish-brown when thick, yellowish when thin, and y greenish- 

 blue ; probably therefore it is hypersthene. 



ihese rocks occur commonly round the shores of Lake Taupo. 

 ihe variety called Lithoidite is recorded from Hamaria on the 

 eastern side of the lake by Dr. v. Hochstetter, and from the island 

 ot Motukaiko by Professor Thomas. It is the most remarkable 

 example of banding in a volcanic rock that I have ever seen. 

 Hochstetter, New Zealand, p. 385 ; Thomas, Trans. N.Z. Inst, 

 ^ ol- XX., p. 309 ; Pond, Trans. N.Z. Inst., Vol. xxi., p. 349, 

 analyses Nos. 7 and 8. 



The pumice so abundant around Lake Taupo is no doubt derived 

 jrom these rocks. It contains crystals of sanidine (often mistaken 

 tor quartz) and hypersthene, by which it can \ye recognised wherever 

 « IS found. The sand on the shore of Lake Taupo contains 

 crystals of hypersthene abundantly. It is the Protohypersthene 

 «>* Professor Judd. 



