Bartrum. — The Distribution of Igneous Bocks in Neiv Zealand. 417 



reddish-brown biotite are also very common. Reasons will be given later 

 for the belief that probably a third pyroxene is also present. The hyper- 

 sthene is in fairly idiomorphic crystals, and preceded the augite, whilst the 

 biotite is later, for its large fresh crystals poecilitically enclose pyroxene, 

 iron-ore, and even quartz grains. The pyroxenes all show imperfect schiller 

 structure ; they are occasionally fringed by a Httle bright grass-green 

 hornblende, which from its association appears largely resOrption-prodUct, 

 though perhaps in part outgrowth. Ilmenite is fairly abundant in coarse 

 irregular masses, but magnetite also is common. 



Diagrammatic Sketch (x 45) illustrating Rel.\tions of Zolsite to OTnER 



Minerals, and General Structure. (See Plate XXVIII, fig. 1.) 

 All. = augite ; Hy. = hypersthene ; PI. = plagioclase ; Q. = quartz ; Z. = zoisite. 



Amongst the primary minerals I must finally mention the mineral 

 identified at first by me as apatite, but recognized by Dr. Thomson as 

 zoisite. It is in occasional rather allotriomorphic crystals up to 0-6 mm. 

 in diameter, and one crystal is encased in a zone of iron-ore. In the 

 instance portrayed by the figure above and the photomicrograph of 

 Plate XXVIII, fig. 1, and in one other, the zoisite is enwrapped (by augite 

 in the text-figure) in a manner that makes it certain that it was formed 

 before the later stages of crystallization of the rock, and therefore is 

 primary. The plagioclase includes occasional rutile needles. 



An Undetermined Pyroxene. 



A number of crystals of a pyroxene were observed in this rock, which 

 in many respects greatly resembles hypersthene, but from other consider- 

 ations I am inclined to believe must be referred to a closely allied mono- 

 clinic pyroxene of a series either identical with or analogous to that of 

 which the now well-known enstatite-augite is a member. These pyroxenes 

 show a microscopic twinning lamination parallel to their elongation, and 

 in addition are frequently intergrown with minute plates of obvious mono- 

 clinic pyroxene approaching diopside, besides containing irregular inclu- 

 sions of this latter mineral. The pleochroism distinctive of hypersthene 



14 — Trans. 



