430 Transactions.— Geology . 



A few hundred yards further ou a similar band outcrops, 

 having at its base a layer of fine conglomerate (the particles 

 being about 2 in. in diameter) some 3 ft. in thickness. 



A quarter of a mile west of this spot another exposure 

 occurs, distinctly coarser than that first met with. The whole 

 band, about 10 ft. thick, is composed of fragments of scoriae 

 and volcanic ash up to fin. in diameter, and contains a great 

 deal of wood in minute pieces converted into lignite. This 

 bed can be traced for some distance, but finally dis- 

 appears in the cliff. It reappears, however, half a mile 

 further on, maintaining the same thickness and texture. 

 Scattered through the band at this spot are a considerable 

 number of angular volcanic fragments, many of them being 

 1 ft. or more in diameter. They are imbedded in the grit, 

 and seem to have been thrown out when that material was 

 deposited. The rock is a hard fresh-looking andesite, with 

 minute steam-cavities, showing microscopic crystals of augite 

 and feldspar. (Rock section C, Plate XXIV.) 



Examined microscopically an average section showed a 

 microcrystalline ground-mass similar to that appearing in 

 the other sections described, though containing perhaps a 

 little more feldspar. The porphyritic constituents were iden- 

 tical with those in the other sections, except for the absence 

 of olivine, no traces of which were to be found. In some of 

 the feldspars appeared the same peculiarity as that seen in 

 the section from the Takapuna ash-beds, successive zones of 

 the material of the crystals extinguishing at different angles. 

 Augite and magnetite were very plentiful, the former appear- 

 ing in both large and small crystals, and showing well-marked 

 crystalline form. (Specific gravity, 2-7.) 



From this on westwards for a couple of miles there are 

 frequent outcrops of these ash-beds. In several places they 

 contain large angular included fragments similar to those 

 just described. Here and there they pass into conglomerates 

 whose particles are in some cases considerably waterworn. 

 The conglomerates for the most part, when traced upwards, 

 pass into finer grits. The coarser portions do not contain 

 fossils. In some of these conglomerate beds I found pebbles 

 of Maitai slate. These, about 1 in. in length, were flattened 

 and much more waterworn than the volcanic material. None 

 of this slate has yet been found nearer than Motutapu, an 

 island in the Hauraki Gulf about five miles north-east of 

 Auckland. The inference is that these pebbles have either 

 been derived from beds of slate in the immediate neighbour- 

 hood underlying the Waitemata series, or they have been 

 brought into their present position by the agency of rivers 

 or currents, which have carried them from more distant locali- 

 ties. 



