Haast. — On the Geological Structure of Banks Peninsula. 497 



Thus a sub-marine hill stood here in the young mesozoic sea, of which 

 portions of the summits and the slopes were gradually covered by agglo- 

 merates and brecciated beds. These beds were formed during and after the 

 eruption of quartziferous porphyries, of which here and there portions of 

 the coulees have been preserved. Some of these quartziferous porphyries 

 resemble in every respect those from the Malvern Hills and Mount Somers. 

 They are also accompanied by pitchstones, porphyritic from the presence of 

 numerous well-formed crystals of sanidine or glassy felspar, and occasionally 

 of garnets. Other portions of the quartziferous porphyries, as for instance, 

 the whole coulee of which Manson's Peninsula is formed, have a rougher, 

 more trachytic matrix. They are full of grains and small crystals of white 

 greyish or smohy quartz. The brecciated beds have a hard felsitic matrix, 

 and the angular fragments of rock enclosed in them belong to a variety of 

 eruptive rocks of many colours, and of different texture, often forming a 

 rock of striking character. They appear conspicuously on the summit of 

 Gebbie's Pass, having been washed into cliffs of picturesque forms, and 

 covering the palaeozoic sedimentary beds from one side of the pass to the 

 other. After the 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 Gebbie'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, breaking 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 Gebbie'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. 



The oldest crater, of which the principal boundaries can be traced at the 

 present time, is the Lyttelton Harbour caldera, having a general diameter 

 of about two miles, the centre of which is situated a little to the south of 

 Quail Island. The general structure of this crater, even before the Christ- 

 church and Lyttelton Eailway tunnel was entirely pierced through, could 

 easily be made out by studying the numerous sections exposed in many 

 directions, and by ascending the steep escarpments of the caldera wall, 

 where a succession of streams of stony or scoriaceous lava, interstratified 



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