Smith. — Alkaline and Nephcline Rocks, Westland. 127 



or segerine-augite in fine grains. This rock also exhibits the 

 phenomena of leucocrasia. The patches consist of a hypidio- 

 morphic aggregate of anorthoclase and a deep-green hornblende. 

 In the normal rock the crystals of hornblende occasionally 

 attain a length of 2 cm. The pleochroism — (a) very pale- 

 brown, (b) brown, (c) dark-brown — shows the hornblende to be 

 barkevikite ; but in the abnormal rock represented by the 

 leucocratic patches the pleochroism of the hornblende is — 

 (a) very pale-yellow, (b) olive-green, (c) yellowish-green — and 

 the mineral is probably common hornblende. 



101. Vogesite. The groundmass of this rock is largely com- 

 posed of an alkali feldspar, with panidiomorphic development, 

 associated with a small quantity of a colourless mineral with a 

 higher refractive index and low polarization tints. A chemical 

 test for mellilite was made, but did not result in the precipita- 

 tion of any gypsum needles. The mineral is therefore not 

 identified. The phenocrysts are colourless to pale-pink augites 

 and pale-brown hornblendes, with perfect outlines, and exhibit- 

 ing a great variety of sectional shapes. Both minerals occur 

 in two generations. The augite is often surrounded by a thin 

 green resorption boundary of crypto- cry stalline segerine or 

 eegerine-augite. Some of the larger hornblendes attain a 

 length of 4 mm., and the pleochroism shows them to be barke- 

 vikite. (Plate XIX, fig. 12.) 



95. A rock differing from the last described, in that the 

 feldspar is distinctly determinable as anorthoclase, and occurs 

 in smaller proportions. The augite in the groundmass is in 

 shapeless colourless grains. Some of it is serpentinised, and 

 the porphyritic augites are also attacked. Crystals of partially 

 serpentinised olivine with a peripheral border of magnetite are 

 not infrequent. The hornblendes, although not so prominent 

 as in the former rock, possess good crystallographic outlines. 

 (Plate XIX, fig. 14.) 



116. This is an intermediate rock between the vogesites 

 and the camptonites. It resembled No. 95, except that ser- 

 pentinisation is more advanced, and plagioclase is present, but 

 not to the same extent as the anorthoclase. 



123. Is also an intermediate rock, the alkali and Hme-soda 

 feldspars being about equal in quantity. In addition to the 

 hornblendes — which here assume a more tabular habit, with 

 a tendency to lose their idiomorphism — there occurs an 

 occasional plate of deep-brown biotite and a few large pheno- 

 crysts of perthite. The perthite is surrounded by a zone of 

 partially untwinned plagioclase, and, in addition to simple 

 Carlsbad twinning, some phenocrysts are Baveno twins. Pseudo- 

 morphs of serpentinous material after augite are present, 



