Speight. — The Geology of Banks Peninsula. 371 



in height, but which rise in places to close on 2,500 ft., and it is specially 

 noteworthy that the highest points of these ridges do not occur near their 

 proximal end. 



Kaituna Valley is about seven miles in length, and runs in a general 

 south-westerly direction along the south-eastern side of Mount Herbert. 

 Its head reaches back to the main divide of the peninsula which joins 

 Mount Herbert on to the crater-ring of Akaroa. Its walls are steep, since 

 it has followed generally the line of flow of the lavas from Lyttelton — i.e., 

 it has the characteristics of a stream-valley running with the dip of the 

 beds. Its floor is flat and deeply covered with alluvium, but about one- 

 third of the way up from the entrance it contracts somewhat where the 

 valley takes a right-angled turn, and farther up it opens out into a wide 

 amphitheatre-like head which a number of valleys of the region present ; 

 it thus reaches to the head of the Little River Valley on the east. 



To the north of the main divide lie Port Levy and Pigeon Bay, the 

 former to the east of the Lyttelton crater-ring, but eroded for the most 

 part from the lavas poured out of that vent ; but a part of the walls on 

 the eastern side of the valley no doubt belong to Akaroa. Its head is 

 divided up into separate valleys like Little River, and it presents few of 

 the features which would suggest that it was a separate centre of volcanic 

 action. Pia;eon Bav has similarly been eroded out of the flanks of the 

 Akaroa volcano, and it closely resembles in form and depth the adjoining 

 bay on the west. It has, however, a broader-headed valley, which has cut 

 into the crater-ring of Akaroa on the eastern side, and farther west reaches 

 to the main divide of the peninsula, where lie the high peaks of Mounts 

 Sinclair and Fitzgerald. 



Neither Pigeon Bay nor Port Levy is truly radial in arrangement, and 

 both appear to have been eroded to some extent out of ground where the 

 flows from the two volcanoes mutually interfered with each other and were 

 probably intercalated along the line of junction. 



The drainage areas of Little Akaloa, Okain's Bay, and Le Bon's, and 

 also that of Peraki, on the south side of the peninsula, reproduce on a 

 smaller scale the features of Pigeon Bay and Little River, and have steep- 

 walled sides and amphitheatres at their heads. 



C. GEOLOGICAL HISTORY. 



1. Trias- Jura Sedimentary Series. 



(See fig. 2.) 



The oldest rocks exposed on the peninsula consist of a series of slates 

 and greywackes with beds of chert and jasperoid rock occurring to the 

 south of Lyttelton Harbour. They form almost the whole of the spurs 

 which stretch down from the Gebbie's Pass ridge towards the head of 

 the harbour, also the points round the indentation known as the Head 

 of the Bay, and stretch in an easterly direction across the base of Potts 

 Peninsula, extending for half a mile up the valley and on its eastern side, 

 projecting as a narrow fringe under the later volcanics. They form the 

 basement beds under the flat-topped ridge running north from Mount 

 Herbert towards Potts Peninsula, being exposed on both sides under the 

 cap of basalt forming its summit. Greywackes and slates also occur on the 

 western flanks of Mount Herbert across the divide between the harbour 

 and McQueen's Valley, forming the rocks round the heads of the streams 

 running therefrom, and reappearing as inliers on the western side of McQueen's 



