Speight. — The Geology of Banks Peninsula. 373 



region of Canterbury, and have been definitely determined as Jurassic from 

 plant fossils found at Mount Potts, dent Hills, and Malvern Hills, and 

 therefore should be assigned to the Maitai system of Marshall, which is of 

 Trias- Jura age. 



Overlying these submetamorphic rocks is a series of different texture, 

 having more the character of a freestone, which has been classified previously 

 as later than the rhyolite volcanic phase,* but which more detailed examina- 

 tion has convinced me represents a deposit antedating the rhyolite eruptions. 

 These beds are developed at the head of Governor's Bay, where they are at 

 least 30 ft. thick, and may be much more, as the upper and lower boundaries 

 of the occurrence are nowhere visible. The rock is here pinkish in colour, 

 free in the grain, and without well-marked bedding-planes. Under the 

 microscope it is highly quartziferous, with some admixture of feldspar and 

 occasional shreds of mica, and therefore is similar in mineral composition 

 to a greywacke, and may have been derived from the same land-mass as 

 furnished the associated greywackes. This bed has, however, yielded no 

 fossils by which its age and true relations can be determined. 



Although the contacts of this occurrence are not clear, exposures of 

 similar rock at Little Quail Island, at the end of Potts Peninsula, and about 

 half-way along its western side show that it undoubtedly underlies the 

 rhyolite ; and farther round the head of Charteris Bay near the wharf, 

 and on the peninsula to the west of the bay, this facies of the sandstone 

 also underlies the rhyolite, and overbes directly, without the intervention 

 of volcanic material, the basement slates and greywackes. It is therefore 

 very probable that the Governor's Bay cccurrence is in the same strati- 

 graphical position, but whether it rests conformably or unconformably on 

 the greywackes it is impossible, to say at present. 



This rock has been quarried for building purposes in several places, 

 especially at Governor's Bay, Little Quail Island, and on the eastern and 

 western sides of Charteris Bay. Where any stratification can be observed 

 the beds strike N.E.-S.W., and in places this has been so perfect that large 

 flags suitable for paving and for the making of grindstones were easilv 

 obtained. Bound the shores of Charteris Bay and at Little Quail Island 

 these sandstones are completely intersected by the trachyte dykes of a 

 later age. which will be referred to hereafter. 



o 



2. First Volcanic Phase. 



The Jurassic rocks were deeply eroded before the first phase in the 

 volcanic history of the district began, and the unconformity is most marked, 

 since the first volcanic beds he right across the edges of the Jurassic sedi- 

 mentaries. The matter produced at this stage is exclusively of rhyolite, 

 and is typically developed near the head of Lyttelton Harbour. Rhyolite 

 rocks are visible about half-way along the cliffs of Quail Island facing the 

 town of Lyttelton, extending in one place almost to the summit of the 

 island, and they reappear on the south side, where they form the solid 

 material of the foreshore and the slopes immediately behind it, flows and 

 beds of agglomerate stretching without intermission, except from dykes, 

 from near the wharf at the east end of the island, behind the quarantine 

 buildings, to its extreme south-westerly point. The rhyolites are exposed 

 along the eastern shore of Charteris Bay, above the narrow band of sedi- 

 mentaries occurring there, and again on the southern shore of this bay, 



* J. von Haast, Geology of Canterbury and Westland, 1879. p. 327. 



