Smith. — Alkaline and Nepkeline Rocks, Westland. 129 



with the isotropic matter present, approach closely to the rocks 

 named " teschenites " by Hohenegger. 



57. A porphyritic diabase from the Te Kinga boss. Mega- 

 scopically it appears to be a feldspar porphyry, but under the 

 microscope the basic nature of the rock is apparent. The large 

 feldspar phenocrysts are labradorite, with a maximum ex- 

 tinction-angle of 42° ; they show incipient epidotization, and an 

 alteration into muscovite. The groundmass consists of ragged 

 crystals, needles, and microlites of a basic feldspar, with a tend- 

 ency to crystallographic development, set in a micro-granular 

 augite arranged interstitially to the feldspar. Iron-ore is plenti- 

 fully distributed through the rock as dust, cubes, and longer 

 rectangular sections ; the two former are magnetite, but the 

 longer sections may be ilmenite. Some of the augite is ser- 

 pentinised. 



91. A rock intermediate between the diabases and the basic 

 lamprophyres. Here the feldspars have almost disappeared, 

 but what there is still bear the same relations to the augite of 

 the groundmass as in the diabases. Augite is the dominant 

 mineral, and occurs in two generations, the intratelluric as 

 plates idiomorphic towards the augites of the groundmass, but 

 not possessing good crystal faces, and in the groundmass as 

 granules. Another form, as diopside in pi enocrytts, is present 

 with good outlines. There is a little hornblende, which ap- 

 pears to be a secondary mineral, as is also a clear serpentinous 

 aggregate occasionally seen in small plates. A little secondary 

 quartz fills cavities in the rock. The accessory feldspar is 

 labradorite. 



By the gradual assumption of the hypidiomorphic structure 

 these rocks pass into theralites and gabbro-diabases. From 

 what is known of the Hohuna Range, a large granitic boss clothed 

 with a dense mass of vegetation up to the winter snow-line, and 

 with few exposed rock-surfaces below that altitude, it is doubtful 

 whether the whole of the rocks herein described do not come 

 to the surface in the hypabyssal form. Although many 

 sections have been made of the granitic rocks from this and 

 the Te Kinga boss by the author and others, so far no nepheline 

 syenites with which tinguaites, camptonites, and allied rocks 

 are usually associated have been found. It is possible the 

 gabbro-diabases may form a marginal apophysis of the granite 

 mass. As boulders the gabbro-diabases are no more common 

 in the fluviatile gravels of the New River system than the voge- 

 sites and camponites, and do not occur so frequently as the 

 tinguaites. In the beds of the mountain torrents draining the 

 northern slopes of the Hohunas they appear to be more common, 

 but there is no evidence that they outcrop at the surface in 

 5 — Trans. 



