374 Transactions. 



and after a break they continue west, forming the greater part of the pen- 

 insulas stretching into the upper part of the harbour. On the eastern one 

 the rhyolite occurs only on its distal end, the proximal end being of sedi- 

 mentaries overlain by basic volcanics, but on the western peninsula the 

 rhyolite extends from its extremity right up to the base of the steep slope 

 immediately below the prominent peak of Cooper's Knob, on the Lyttelton 

 crater-ring. After an interval of sedimentaries it appears again in the 

 vicinity of Gebbie's Pass, forming the prominent hills in its immediate 

 vicinity, stretching down on either side of the stream running there- 

 from, and forming the main mass of the spur between Gebbie's Valley 

 and McQueen's Valley ; an isolated block occurs on the eastern side of 

 the latter valley, and a small outcrop also occurs on the east- side of the 

 Teddington Valley, to the north-west of Mount Herbert, just opposite 

 Mr. Wilson's house. The only evidence of a wider extension of the 

 rhyolite under the covering of later basics is furnished by a tuff con- 

 taining rhyolite pebbles on the east side of Onawe Peninsula. Akaroa, 

 this being the only known occurrence on Banks Peninsula outside the 

 Lyttelton area. 



In several places, as at Quail Island, near the summit of Gebbie's Pass, 

 and on the shore of Charteris Bay, the lowest beds exposed consist of agglo- 

 merate, composed of subangular boulders of all sizes up to 3 ft. in diameter. 

 In McQueen's Valley there is a well-developed breccia with pitchstone frag- 

 ments. Among the rhyolitic material are occasional foreign elements, such 

 as pebbles of greywacke and fragments of an andesite differing in character 

 from the olivine-bearing andesites or andesitic basalts that were extruded 

 later. Where this came from it is quite uncertain, since no exposure of 

 similar rock in position has been located. The rhyolitic material includes 

 banded rhyolites with irregular wavy bands of microspherulites, garnet- 

 iferous rhyolite, mica rhyolite of various shades of colour — green, white, 

 and pink — as well as fragments of pitchstone. The mass has weathered 

 into fantastic forms, with large globular cavities a striking feature. 



Wherever these fragmentary deposits occur they are apparently at the 

 base of the series, but in some cases solid rhyolite flows rest directly on 

 greywacke and slate. The rock is typically of white colour, but is occa- 

 sionally pinkish. In some places it shows dark-coloured phenocrysts of 

 smoky quartz, and in others sanidine crystals If in. in length stand out on 

 weathered surfaces. In many places, however, phenocrysts are not visible 

 to the naked eye. At the back of Quail Island it is markedly spherulitic 

 in places, with spherulites up to 3 in. in diameter, but here, as in other 

 places, it appears to have been markedly silicified after eruption, no doubt 

 by the action of warm waters laden with siliceous material percolating 

 through the mass of rock. The alteration produced by this action is in 

 some instances very pronounced, and as it has involved other rocks as well 

 it is sometimes extremely difficult to determine the relations to the beds 

 with which they are in contact. I have found this specially so on the 

 shores of Charteris Bay. 



The rhyolite is penetrated by dykes of trachyte and basalt belonging 

 to a later period, and also by dykes of rhyolite and pitchstone which 

 are apparently contemporaneous with the rhyolite-flbws. The most note- 

 worthy of these occur near the crest of the Gebbie's Pass ridge, on the 

 summit of the hill west of the road. The pitchstone dyke strikes east and 

 west and is 50 ft. in width, and close alongside it to the north is a dyke 

 of rhyolite with similar orientation and well-developed columnar structure. 

 Another rhyolite dyke forms the summit of a hill to the north-west of this. 



