Speight.— Soda Amphibola Trachyte. Ill 



later date, and considered that the peninsula was built princi- 

 pally from the centres of Lyttelton and Akaroa. I cannot 

 speak definitely from personal observation as regards this point, 

 but from what I have seen I am inclined to think that it is un- 

 likely that a crater occupied the valley of Little River, but that 

 the lavas occurring there were poured out from both Lyttelton 

 and Akaroa, and that the form of the valley can be well ex- 

 plained as the result of prolonged stream erosion. When all 

 the lavas are basalts and basic andesites, and good sections 

 showing their relations are practically absent, an accurate 

 estimate is extremely difficult to make. Good sections showing 

 contacts of the andesites with the earlier rhyolites are also rare, 

 owing to the completeness with which the soil covers over every- 

 thing. However, a section near the end of the spur which 

 divides Gebbie's from McQueen's Valley affords convincing 

 proof of their relative age. Here the actual contact is seen, 

 and andesites undoubtedly overlie denuded rhyolites. 



The andesites always contain augite, with a small amount 

 of olivine generally added, and thus show close relations to the 

 basalts ; but the silica percentage of some varieties is too high 

 (about 56) for them to be classified as such. There are grada- 

 tions, however, from the less basic to the thoroughly basic types, 

 which finally pass into undoubted basalts. It is highly likely 

 that the Akaroa lavas are of a slightly later date than those 

 from the Lyttelton volcano. They are generally of a more 

 basic character, true basalts forming a large proportion of effu- 

 sive mass. This evidence is perhaps very unreliable, but it is 

 supported by the fact that the crater-ring of Akaroa is in a much 

 more perfect condition than the Lyttelton ring, denudation not 

 having exerted such a marked influence over its original form. 

 However, this may be accounted for by the more resistent 

 character of the rocks constituting it. In the subsequent sec- 

 tion I have represented the Akaroa lavas as being slightly 

 younger than the Lyttelton ones. 



The andesitic eruptions from these two centres were suc- 

 ceeded by an outpouring of basalts and andesites from Mount 

 Herbert, and probably from Mount Sinclair. The latter moun- 

 tain forms the geographical centre of Banks Peninsula, being 

 situated at the junction of the Port Levy, Pigeon Bay, and 

 Little River Valleys, with outlying parts extending nearly to 

 the edge of the crater-ring of Akaroa. 



Sir Julius von Haast mentions a fourth centre of eruption 

 at Quail Island, within Lyttelton Harbour; but this may be 

 contemporaneous with that at Mount Herbert, and it is even 

 possible that the Quail Island basalts came from Mount Herbert, 

 and that the connecting rocks have been removed by denudation. 



