Speight. — The Geology of Banks Peninsula. 383 



The flows belonging to this series rest almost entirely on the basic rocks 

 of the previous series all round the heads of the valleys reaching down to 

 Purau, Charteris Bay, and the Head of the Bay on the north side, but on the 

 east side of Charteris Bay they rest on rhyolites : in Port Levy and Kaituna 

 Valley they again rest on the older basic rocks. (See fig. 2.) 



Where the underlying rocks of the Lyttelton system are exposed they 

 give the idea that even at that period the cavity resembled to some extent 

 that at present existing and that it was of the caldera form, and this 

 suggests that a long period of time elapsed between the two basic series of 

 flows. This point is also emphasized by the juvenile character of the 

 drainage which has established itself on the long gentle slope running down 

 from the summit of Mount Herbert Peak. The period of these eruptions 

 is therefore in all probability late Tertiary, and may agree with those which 

 took place at Timaru, which are in all probability of Pliocene age. seeing 

 that the lavas lie there on an eroded surface of Upper Miocene rocks and 

 that underneath the flows fossil bones of Dinornis have been obtained. 



The lava-flows from Mount Herbert are exclusively basalts, most of 

 which are extremely fine-grained in texture, but a few are coarse in 

 character. No system of dykes similar to that associated with Lyttelton 

 or Akaroa occurs in connection with this outburst from Mount Herbert. 



(I).) Mounts Fitzgerald and Sinclair. 



To this stage in the volcanic history the two authorities cited above 

 assign outbursts at Mount Fitzgerald ard Mount Sinclair, which lie on the 

 ridge connecting the two great cones, and, indeed, form its highest summits. 

 The lavas of these two peaks are exactly the same as those erupted from 

 Akaroa, and there appears to me to be no justification for calling them 

 separate volcanoes. Their lava-streams show an inclination which leads 

 one to think that they flowed from Akaroa ; and, though they appear to 

 lie beyond the limits of the crater-ring, they are no farther from the centre 

 of the caldera than similar heights on the eastern side of the harbour about 

 which there has never been any doubt. They apparently lie far out, but 

 this effect is due to the fact that at the head of Pigeon Bay the external 

 stream erosion has cut far into the edge of the crater-wall — in fact, a portion 

 of the internal drainage of Pigeon Bay Peak and its neighbourhood, which 

 should go towards Akaroa Harbour, flows into Pigeon Bay. whose streams 

 are thus capturing the heads of those on the other side of the ridge. Thus 

 it is that the crest-line of the hills round the harbour takes a remarkable 

 bend in at this point, and the headwaters of Pigeon Bay on its western side 

 have cut in circumferentially along the strike and apparently separated the 

 elevations from the walls of the crater. There appears to me to be no 

 reason why they should be regarded as separate centres of eruption, and 

 after careful examination I must withdraw my former endorsement of 

 Haast's and Hutton's opinion.* 



5. Fourth Volcanic Phase. 

 Quail Island. 

 The final stage in the volcanic history of the peninsula was the forma- 

 tion of Quail Island (Plate XXV), which represents in all probability a 

 secondary cone within the crater-ring of Lyttelton. The basement of the 



*R. Speight, On a Soda-amphibole Trachyte from Cass's Peak, Banks Peninsula, 

 Trans. N.Z. Inst., vo'. 40. 1908, p. 176. 



