178 



Transactions. 



On examining a map of Banks Peninsula it will be seen 

 that the centres of volcanic activity lie approximately on a line 

 running east-south-east and west- north- west. It seems, there- 

 fore, a reasonable inference that the eruptions took place at 

 different points of a fissure or line of weakness in the earth's 

 crust running in that direction ; that eruptions broke out first 

 at the Lyttelton end of the fissure, and that afterwards the 

 centre of maximum disturbance moved eastward to Akaroa, 

 and then back to Mount Sinclair and Mount Herbert, and possibly 

 to Quail Island. 



As the Lyttelton volcano has thrown out rocks belonging 

 to three different periods, and perhaps to four, I think it would 

 be convenient to refer to the rhyolites as the Gebbie's Pass 

 series, to the olivine-andesites as the Mount Pleasant series 

 (named from one of the chief peaks on the northern side of the 

 harbour immediately behind the Town of Lyttelton), and to 

 refer to the lavas which come from Mount Herbert as the Mount 

 Herbert series. All these are quite distinct in age : the Gebbie's 

 Pass series being almost certainly Cretaceous, the Mount Plea- 

 sant series being early Tertiary, and the Mount Herbert series 

 middle Tertiary ; but the last two are extremely uncertain as 

 regards their age, and may be much more recent. Although 

 stream erosion has exerted a marked influence in forming valleys, 

 yet the form of the crater-ring is fairly perfect, especially as 

 regards Akaroa, so that a more recent date may very well be 

 assigned to the two later series. 



Diagrammatic Section of Banks Peninsula, from Tai Tapu to the 



Coast near East Head. 



1. Slates and groywackos ; Lower Mosozoic(?). 2. Rhyolites, Gebbie's 

 Pass series ; Cretaceous. 3. Augite-andesitoa and basalts, Mount 

 Pleasant series ; early Tertiary(?), perhaps later. 4. Basalts and 

 andesites, Mount Herbert series ; mid Tertiary!?), perhaps later. 

 5. Syenite, Onawe Peninsula; early Tertiary (T), perhaps later. "! 



Note. — The line of this section is not straight, but altered 'in 

 direction to show the relative position of the rocks of different age. 

 A l">"<I deal of the section is problematical, particularly that portion 

 between Mount Herbert and Akaroa Harbour. 



