600 Transactions. — Geology, 



Returning to tlie orifice or orifices from which the material for the for« 

 mation of the caldera wall was ejected, and to which also the numerous dykes, 

 mostly having a vertical position, intersecting it, can he traced, it appears 

 that the principal focus of eruption was situated a little to the south-west of 

 Quail Island, as the greatest portion of the dykes radiate from here, and 

 the eastern and southern sides of Quail Island, and the shores near 

 Charteris Bay, are formed of tufaceous agglomeratic and hrecciated heds, in 

 which a number of angular blocks of rock are enclosed, having all a very 

 bleached appearance. 



It would go beyond the limits of this address were I to follow the further 

 genetic history of Banks Peninsula in all its details. I can, therefore, only 

 indicate here in a few words how the whole, in course of time, has been 

 built up. Simultaneously with, or shortly after, the Lyttelton caldera, the 

 Little Eiver caldera, of which only a small portion remains, was formed in 

 the same manner. The formation of the largest of the whole series, the 

 Akaroa caldera, is next in age, which, with the exception of a small portion 

 of its northern rim, is perfectly well preserved. After their formation, new 

 eruptions, and of a different form, took place south of the Lyttelton caldera 

 and north of the Little Eiver and Akaroa calderas, during which the highest 

 portion of Banks Peninsula was built up — Mount Herbert, 3,050 ; Castle- 

 hill, 2,900 ; and Mount Sinclair, 2,800 feet ; only portions of the craters of 

 these younger systems are still preserved, but easily recognized when 

 standing on the summits of these mountains. The southernmost portion 

 of the Lyttelton caldera was partly destroyed or covered by lava-streams 

 belonging to the Mount Herbert system, also of a basic (basaltic) nature, of 

 which a whole series flowed into it, now forming the huge spurs descending 

 from the summit of Mount Herbert into the harbour between Charteris 

 and Khodes Bays. The last eruption, of a submarine character, took 

 place in the centre of the Lyttelton caldera, by which Quail Island was 

 formed. 



I shall now proceed to offer you some observations on the system of 

 dykes, which are so well developed in the Lyttelton caldera. The most strik- 

 ing facts in connection with the system of dykes of the caldera, and to 

 which I have devoted considerable attention, are their size, longitudinal extent, 

 and constancy in direction. From the researches of numerous observers, 

 it has been proved that all the dykes of Mount Vesuvius and Mount Etna 

 do not extend much beyond the centres of eruption, so that they advance 

 only a short distance, and, rapidly thinning out, soon disappear, a fact 

 which my own observations along the crater walls of both mountains have 

 amply confirmed. However, I have no doubt that other volcanoes similar 

 in construction to Banks Peninsula, and differing as considerably from 



