420 Transactions. 



is largely converted to a finely fibrous, tufted, alnnost colourless aggregate 

 bordered by green ; it is referred with some diffidence to tremolite and 

 actinolite. 



NORITE, 

 Wairau Creek, Milford, Auckland. 



I found a very-well-rounded boulder about 5 in. in diameter included 

 in the sandstones of the Waitemata beds at the mouth of Wairau Creek, 

 a little north of Lake Takapuna, and quite unaccompanied by other 

 boulders or pebbles. It is a very coarse norite with plagioclase (medium 

 labradorite) a little more plentiful than the ferro-magnesian minerals, which 

 are hypersthene (including an alhed pyroxene dealt with on p. 417) and 

 less abundant diallage. The hypersthene is being converted into talc, and 

 particularly adjacent to cracks there is chloritization and the entrance of 

 fine pyrite. 



DOLEEITE, 

 Swinging-basin, Silverdale, Auckland. 



This occurs as coarse angular blocks several feet in diameter, unearthed 

 during excavation for the swinging-basin at the Silverdale (Wade) wharf 

 on the Welti Stream, which flows to the east coast about twenty miles north 

 of Auckland. Though apparently the actual outcrop is not laid bare, yet 

 this cannot be far distant, unless — a suggestion their comparative freedom 

 from weathering would negative — the blocks come from the formerly over- 

 lying Waitemata beds now removed by erosion froTto the stratigraphically 

 lower hydraulic limestone of this area, but which contain large blocks of 

 andesite and perhaps other igneous types not far distant on Whangaparaoa 

 Peninsula. The site of discovery of the dolerite is immediately adjacent 

 to where McKay maps one of his serpentine dykes* (which, however, I 

 was unable to locate during my brief visit), and the idea suggested itself 

 that there might be some connection between the intrusion of the two 

 rocks. Professor W. N. Benson remarks anent this point, after examination 

 of the dolerite section, " It ,does not contain albite, and is more like the 

 post-peridotitic than the pre-peridotitic of my New South Wales dolerite 



dykes."t 



Macroscopically the rock is a very dark finely holocrystalUne type with 

 inconspicuous glistening lath-like feldspars and prominent chloritized ferro- 

 magnesian mineral. In section the most striking feature is the ophitic 

 structure ; the mass consists largely of large labradorite laths, between 

 which is faintly pleochroic partially chloritized pink augite in somewhat 

 columnar crystals, and a profusion of irregular iron-ore growths and skeleton 

 crystals enwrapped by the pyroxene (see photomicrograph, Plate XXVIII, 

 fig. 2). The feldspars are fairly fresh, but a Uttle secondary calcite and 

 a very great deal of chlorite developed from the augite are present. 



BASALT, 



" SuGARLOAF," Matakana-Leigh Road, Rodney County. 



The " Sugarloaf " is a conical knob a little west of the main road from 

 Matakana to the Omaha, and about two miles from Matakana. It is mapped 

 as igneous by Cox in his report on the geology of the Rodney and Marsden 



* A. McKay, On the Occurrence of Serpentine Dykes in Cretaceo-Tertiary Strata 

 near the Wade, Auckland, Rep. Geol. Explor. during 1883-84, pp. 99-101, 1884. 

 t Letter dated 13th September, 1918. 



