Canterbury and Westland. 327 



formation of the brecciated agglomerates, new eruptions of acidic rocks 

 took place, now in the form of rhyolites, the highly liquid matter 

 reaching the surface through broad channels, of which one has been 

 preserved as a large dyke, forming a beautiful section on the northern 

 side of Grebbie's Pass, not far from the summit. The dyke is here 

 about 100 feet thick, half of which is formed by the central portion, 

 consisting of a whitish rhyolite with a fine laminated structure, break- 

 ing in prismatic blocks ; the rest on both sides, where in contact with 

 the agglomerates, has cooled more rapidly, and has assumed the 

 character of an obsidian. This obsidian is greenish or brownish 

 black, very brittle, and imperfect crystals of sanidine are enclosed in 

 it. This dyke can be traced for a considerable distance upwards. 

 "Where overflowing and covering the agglomerates it forms the highest 

 peak on the western side of Grebbie's Pass, well visible from Lyttelton 

 Harbour. The rock here is divided into small pentagonal columns, 

 with a vertical arrangement; lower down the Pass, the same coulee has 

 a tabular structure. There is no evidence from which we can conclude 

 when these beds were raised above the sea, but there is no doubt that 

 this was accomplished in connection with volcanic disturbances close 

 to them, beginning probably towards the latter part of the tertiary 

 period, when the foundation of the oldest crater in Banks' Peninsula 

 was laid. It is, however, clear that before and during that time, these 

 quartziferous porphyries and agglomeratic beds underwent considerable 

 denudation and disintegration, because we find at their base deposits of 

 thick bedded sandstones, consisting almost entirely of grains and crystals 

 of quartz, not very strongly adhering together, an imperfection detracting 

 considerably from the value of this otherwise beautiful freestone. 

 That these quartzose sands were deposited over a considerable area can 

 be concluded from their occurrence in different localities, at consider- 

 able distances from each other, the principal ones being situated at 

 Ohinitahi (near the head of Lyttelton Harbour), at Little Quail 

 Island (between Quail Island and the mainland), and some way inland 

 in Charteris Bay. Little Quail Island has been preserved under 

 peculiarly favourable circumstances, as close by numerous volcanic 

 eruptions have taken place, of which the latest formed the greater and 

 highest portion of Quail Island. 



Owing to the fact that agglomerates, consisting of volcanic boulders 

 and pebbles, occur about 1,500 feet above the sea-level on the flanks of 

 Castle Hill, I came to the conclusion, during my first examination of 

 Banks' Peninsula, that the volcanic rocks of which it has been built up 



