Speight. — The Geology of Banks Peninsula. 375 



( )n the southern side of the ridge Haast notes a dyke running north-east 

 across the gully up which the road goes. It appears as a well-defined mass 

 of markedly silicified rhyolite resembling a dyke in its field occurrence, but 

 in all probability is a flow which has been tilted by earth-movements sub- 

 sequent to its extrusion. 



It is difficult to locate the centre from which the rhyolites were erupted. 

 The dykes — excluding from consideration those of later date, which are 

 of no value in this connection — do not show any radiating arrangement 

 (fig. 3), but the flows and ash-beds on Quail Island show a well-defined 

 dip to the north, and those in Governor's Bay. though somewhat irregular, 

 dip to the west and north-west in general, and those in Charteris Bay to 

 the east, so that it seems probable that the centre should be located some- 

 where near the area now occupied by the Head of the Bay. The present 

 thickness of the deposits, allowing for denudation, does not point to any 

 mass of material having been poured out at all comparable with that from 

 other centres of rhyolitic activity in the province, and as the direction of the 

 flows at the commencement of volcanic activity would in many cases con- 

 form to the shape of the land surface on which the volcanic material was 

 poured out a few observations of the inclinations of beds in a case like 

 that under consideration may give a somewhat unsatisfactory result. This 

 is well exemplified on the west side of Potts Peninsula, where the rhyolite- 

 fiows overlie immediately the earlier sedimentaries, and exhibit a marked 

 variation in the direction and amount of inclination. The clearest case 

 of bedding is to be observed on the south side of Quail Island on the 

 point between the two groups of buildings, and also on the south side of 

 the point to the south of the Leper Station. In these places the strata 

 dip to the north and north-east at angles of about 20°, so that we can 

 say for certain that the volcanic focus lies to the south or south-west of 

 Quail Island. 



An interesting deposit of fossil leaves and stems of dicotyledonous 

 plants is mentioned by Haast* as occurring on the south side of Gebbie's 

 Pass in sandy shales associated with coarse sands and loose conglomerate. 

 These have a strike in an E.N.E.-W.N.W. direction- — that is, parallel to 

 the great band of rhyolite thought to be a dyke by Haast. This is 

 distant only a few chains, and its steep inclination accords with that of 

 the leaf-beds, which dip to the S.S.E. at very high angles, approximately 90°. 

 It appears to me, therefore, that the inclination of both the band of 

 rhyolite and the leaf-beds is to be attributed to tilting after deposition 

 as a result of folding or other deformational movement. As far as can be 

 ascertained, the material of which the sands and conglomerate are composed 

 is entirely volcanic in origin, and it is probable that it represents the lowest 

 beds of fragmentary rhyolitic material which occur elsewhere, and that 

 the plants are the remains of the vegetation on the land surface on which 

 the volcano was originally established, and formed in much the same way 

 as the deposits of timber in the pumice to the east of Ruapehu and 

 Tongariro, in the North Island, which is a remnant of the old forest cover- 

 ing of the land in the vicinity of the volcanoes. This idea is supported 

 by the fact that a short distance farther up the valley is a small inker of 

 Trias-Jura sedimentaries, which can be only a few feet lower in the strati- 

 graphical sequence than the plant-beds, and which no doubt lie close under 

 them at the spot where they occur. No good sections are available, how- 

 ever, and the field relations are obscure. 



" J. von Haast, loc. cit., p. 326. 



