Fox. — The Waitemata Series. 477 



powder when, after grinding a section, one slowly withdraws 

 the slide at right angles to the iron plate, the markings occur- 

 ring both on the plate and on the slide. Possibly the dendritic 

 markings on the zeolites were formed in an analogous 

 manner. 



The lava fragments are so small and so oxidized that I was 

 not successful in making any microscopic sections. My sec- 

 tions of the grit were scarcely more successful, the rock 

 crumbling away before it was thin enough to be of much 

 service. In one or two instances fragments of lava could be 

 recognised in the sections, containing feldspar and six-sided 

 augite phenocrysts and probably an augite-andesite. 



Among the crystals in the tuff corroded quartz grains 

 occur, which may be due to the mingling of sandy sediment, 

 or, since Sir James Hector says that the grit contains frag- 

 ments of trachytes, may be derived from them or from more 

 acid rocks. By far the most numerous crystals are small 

 oblong feldspars sometimes altered and milky, at other times 

 fresh and bright, with good cleavage. These are very plentiful 

 throughout the bed. A few broken fragments of augite crystals 

 are also present, but the large perfect augites described as 

 occurring in the Cheltenham breccia are conspicuous by their 

 absence. The grit is largely composed of fragments of greenish 

 sandstones and slates which may be Palaeozoic rocks. Large 

 blocks of sandstone are absent, and current-bedding is unusual. 

 Iron-pyrites is plentifully disseminated in bright-yellow flecks. 

 The black matrix is often studded with scarlet scoria and 

 white feldspars, and forms a handsome rock. From the plenti- 

 ful occurrence of feldspar and augite the grit may be best 

 described as an augite-andesite tuff. 



I do not consider the source of the Parnell grit by any 

 means as certain as that of the Cheltenham breccia, but, on 

 the whole, the evidence is perhaps in favour of a source near 

 Cape Colville. Before giving what evidence there is in support 

 of this I must freely admit that the grit may have come from 

 the Waitakerei vents, like the other volcanic beds of the 

 series. But in the first place it is a good deal younger than 

 the Cheltenham bed, as is shown by the fact that it crosses 

 the Maitai ridge, which apparently was above water when 

 the former bed was deposited ; and so it is quite possible that 

 the Waitakerei vents may have become quiescent. In the 

 second place, it is a bed with a very wide distribution, extend- 

 ing from Ponsonby to Turanga Creek, from Manukau to St. 

 Helier's. Yet it is not a coarse breccia. Such a widespread 

 bed must have been, one would think, the result of very 

 violent eruptions, and if the eruptions at Waitakerei were 

 very violent the bed at the Manukau ought to contain some 



