622 Transactions. 



(1.) Igneous Rocks associated with the Rahia Series. — The largest occur- 

 rence of old volcanic rocks is at Scott Point. In the field this rock shows 

 remarkable spheroidal structure, probably due to movement after partial 

 consolidation of the lava, which gives it a pseudo-agglomeratic appearance. 

 In the more decomposed, clayey material between the harder blocks calcite 

 and chlorite are often developed. 



In hand-specimens the rock at Scott Point is a very fine grained, dull- 

 green and reddish rock, containing no identifiable mineral except secondary 

 calcite, which is abundant, both as finely disseminated grains and also as 

 amygdules. 



Microscopically, the rock, which is somewhat decomposed, and stained 

 yellow with limonite, appears to be an oUvine basalt. The phenocrysts 

 are few, and are feldspar (labradorite chiefly), containing numerous glass 

 inclusions and seldom showing multiple twinning, and olivine with charac- 

 teristic form but largely altered to calcite. The ground mass is made up 

 of elongated feldspar laths, between which are scattered numerous granules 

 of augite. Professor Marshall notes that the rock resembles the basalt 

 near Ahipara and Takahue described by him in a recent paper.* 



Similar igneous rocks occur at Eahia Bay, where, as already stated, 

 they intrude and alter the Rahia Series, and again on the higher sand- 

 shrouded land between Eahia Bay and Cape Maria van Diemen. In this 

 locality, however, it seems doubtful whether or not some of these rocks are 

 contemporaneous flows. 



(2.) Igneous Rocks associated with the Whangakea Series. — Some doubt 

 exists as to the relationship of the apparently sedimentary rocks to the 

 undoubtedly igneous at Cape Maria van Diemen and at Whangakea. At 

 the latter place there is an extensive development of basalt similar to that 

 occurring at Scott Point, though the oUvine crystals are smaller, more 

 numerous, and have been corroded by the action of the unconsolidated 

 magma. Large feldspars are absent, and the small laths show no tendency 

 to arrangement in flow-hnes (Plate LVI, fig. 2). A little to the east of 

 Whangakea is seen a coarser igneous rock — possibly a mica-diorite. Darky 

 Hill and the neighbouring high ridges appear to be chiefly composed of a 

 very compact igneous rock in which a finely crystalline structure and 

 small feldspars are visible to the naked eye. Under the microscope this 

 rock proves to be a somewhat altered augite-andesite, in which fairly large, 

 very light brown augites and elongated feldspars (andesine and labradorite) 

 are the only phenocrysts. The groundmass is now obscure, but contains 

 abundant grains of ilmenite, and was apparently made up of feldspar laths 

 and granules of augite and ilmenite imbedded in a glassy base. 



(3.) Igneous Rocks associated with the Mount Camel Series. — According 

 to McKay, t " intrusive or bedded contemporaneous floes of crystalline 

 rocks — syenite and diorite " occur at the North Cape headland, on the 

 northern coast west of Spirits Bay, and at the head of Parengarenga Harbour. 

 We were able to visit only the first of these localities. 



The rock forming the greater part of the North Cape headland is a basic 

 plutonic showing considerable range in structure and in mineralogical com- 

 position. On the south the plutonic is overlain by grit-beds of Miocene 

 age, while along its western boundary— near Ketr Point — it has intruded 

 and altered argillaceous rocks which may belong to the Whangakea Series. 



* Traus. N.Z. Inst., vol. xl, 1907, p. 82. 

 t Rep. G.S., 1894, p. 90. 



