Yol. 62.] GEOLOGY OF DTJ^EDIX (NEW ZEALAND). 401 



This rock was at first classed as a rhomb -porphyry, but speci- 

 mens sent to Prof. llosenbusch and kindly examined by him, led him 

 to inform me that it would be unwise to use this name in the 

 absence of the characteristic rhomboidal shape of the felspar- 

 phenocrysts. However, he agrees that the rock is a perfect 

 mineralogical equivalent of these rocks, and is the effusive represen- 

 tative of the plutonic laurvigites. I have not made any chemical 

 examination of the rocks of this class, but suggest the name of 

 kaiwekite, after the native name of the Long-Beach locality, 

 Kaiweke. 



Perhaps the most prominent characteristics of the kaiwekites, 

 variable as they are in appearance, are as follows : — (1) The 

 abundance of anorthoclase and various felspathic intergrowths ; 

 (2) the very frequent square and isometric sections of felspars in 

 the groundmass (see PI. XXXIX, fig. 2) ; (3) the comparative 

 absence of coloured rock-forming minerals ; and (4) the frequent 

 occurrence of pyroxene, with a brown centre and an aegirine-margin, 

 and of serpentine-pseudomorphs after olivine. 



In the accompanying geological map (PL XXX VI) the kaiwekites 

 are not specially indicated. They are omitted, because they usually 

 occur as boulders in localities where there are no means of gaining 

 any knowledge as to the relations of the kaiwekite to neighbouring 

 rock-masses. In general it would appear to be intrusive, but at 

 Long Beach it forms a great lava-flow constituting a prominent cliff 

 on the west side of the Bay ; and at WicklifTe Bay there is another 

 lava-flow forming a similar cliff on the north side of the Bay. 



10. Trachytoid phonolites. — The variety of these rocks is 

 very great. They all have an extremely-dense texture and a dark- 

 green colour. In many, no phenocrysts whatever can be distin- 

 guished. I have found it advisable to divide them into four types. 



(A) Logan's- Point type. — Extremely dense. The rock is a 

 dense web of felspar-microliths, and in the meshes are nepheline- 

 crystals, segirine, and cossyrite. The nepheline is hard to distinguish 

 without staining, but after staining it is seen to be a highly-important 

 constituent. It is idiomorphic, while the aegirine and cossyrite are 

 allotriomorphic. The last-named is extremely pleochroic, though in 

 greenish-brown tints. It has a remarkable spongy texture, but all 

 the portions of one of the spongy growths, though often separated 

 by felspar-crystals or nepheline, have a uniform extinction. 



(B) St. Leonard's type. — Phenocrysts of brown hornblende 

 are common, as also occasional phenocrysts of felspar (anorthoclase 

 and oligoclase). The groundmass is a dense growth of felspar- 

 microliths and small grains of aegirine-augite. It is hard to detect 

 nepheline ; but, after staining, this mineral is found to occupy much 

 of the space between the felspars and the segirine- augite grains. The 

 nepheline is allotriomorphic. There is no cossyrite in this rock. 



(C) Andesitic type. — Yery dense. Felspar-microliths show 

 marked flow-structure, but do not constitute a web-like mass as in 

 type A. There are a few phenocrysts of oligoclase. The aegirine- 



