152 Transactions. 
Doleritic. Rocks. 
The rocks described under this heading are believed to represent masses 
intrusive into the Onerahi beds. Certain of them have been found only 
as boulders, but there may be actual outcrop in the headwaters of Orewa 
Stream. All are to be found within a short distance of the cemetery 
adjacent to Parakakau-Silverdale Road. 
The dolerite from Orewa Stream is discoverable only with difficulty. 1% 
occurs as small fragments in the low right bank of the stream, about a 
quarter of a mile west of the cemetery. One large block partially bared 
in a small excavation appears to represent the actual outcrop of a dyke. 
If so, the dyke is likely to be a narrow one, for the rock is much more 
resistant than the surrounding beds, and if in moderate quantity would 
certainly give topographic indications, which are now lacking, of its presence. 
Petrographically the dolerite is a relatively coarse, holocrystalline, poorly 
ophitic rock, made up of about 75 per cent. plagioclase along with almost 
colourless partially-uralitized augite, a little ilmenite, and rare crystals of 
green hornblende. Frequent narrow, white, secondary veinlets have not 
been closely studied, but appear to consist of opal with a little radiating 
zeolite 
olite. 
A little east of the cemetery there are numbers of boulders lying on the 
surface which have very uniform macroscopic appearance, but which when 
sectioned show some variety, though perhaps not greater than is to be 
rest is pyroxene, or uralite derived from that mineral, with a little 
magnetite and occasional picotite. Some small crystals of unaltered though 
marginally resorbed hypersthene are present, but the main mass of the 
pyroxene has been pale augite now almost completely converted to uralite -` 
except in a few parts of the section. А fine-grained, non-porphyritic 
epidiorite shows perfect fine-scale ophitic structure, with some fluxional 
arrangement of the plagioclase (basic labradorite), which here forms nearly 
three-quarters of the rock. The pyroxene is completely uralitized. 
Mr. H. T. Ferrar, of the Geological Survey, kindly supplied the first 
specimen that the writer obtained of these epidioritic boulders. In a 
report furnished to Mr. Ferrar it was suggested that the boulders had been 
shed from conglomerates in the pre-existing Waitemata cover. Later 
collecting, however, has established a comparative uniformity of type which 
contrasts with the diversity usual in the conglomerates, and there can be 
little doubt that the rocks are actually intrusives which penetrate the 
Onerahi claystones of the vicinity 
Basalt near Wray’s House, Horseshoe Bush. 
augite is in numerous sharply idiomorphic zoned crystals, and with it are 
associated very plentiful small flakes of deep-brown biotite. There is a 
moderate quantity of magnetite, whilst apatite is in very long sharp needles. 
The matrix is constituted by weathered laths of plagioclase. 
