Canterbury and Westland. 345 



After the formation of the Akaroa volcano, a long space of time must 

 have intervened, so that great changes by denudation and disintegration 

 could take place before new eruptions followed at different intervals. 

 It is very probable that during that period of comparative repose the 

 barranco leading into the Lyttelton caldera was forming, and that the 

 upper portion of the quartzif erous porphyries, with the quartzose sand- 

 stones resting on their flanks, both forming a portion of the 

 caldera wall where now Grebbie's and McQueen's Passes are situated, 

 together with the lava-streams and agglomeratic beds on both declivities 

 were partly removed ; of the latter some remnants are still to be 

 found near Lake Ellesmere, where the road crosses Grebbie's Mat. 

 After this period of quiescence new eruptions took place from two 

 principal centres, of which the best preserved and highest is situated 

 near the summit of Mount Herbert. It rises on the southern side of 

 Lyttelton Harbour, while the other is found north of the Akaroa 

 caldera, the highest remaining portion being designated Mount 

 Sinclair (2800 feet). I am unable to say which of the two is the 

 earliest, but I shall first speak of the Mount Herbert system, that 

 being the most conspicuous. Several new vents were opened near the 

 rim of the Lyttelton caldera, by which a volcano was built up by 

 lavas-treams, ashes, and other ejecta, rising much above the 

 remnants of the former system. Although much disintegrated, the 

 remaining portions of this newer volcano still rise in Mount Herbert 

 to 3050 feet, and in Castlehill to 2900 feet — the altitudes are taken 

 from the Admiralty chart, with which my own calculations from 

 barometrical observations closely agree. These remains of the newer 

 volcanic cone consist of basic rocks, agreeing much more with those 

 of the Akaroa than with those of the Lyttelton caldera. These basalts 

 are fine-grained, with a peculiar silky lustre, and contain sometimes 

 large crystals of labradonte and small needles of basaltic hornblende. 

 They have often a tabular jointing. Others are lighter in colour, and 

 resemble some of the South American andesites. The scoriaceous 

 lavas have generally a brownish colour with a reddish tiuge. Descending 

 for a considerable distance from the summit of both mountains, we find 

 that the lava-streams lie nearly horizontal, and are interstratified with 

 beds of agglomerate, tufa, and laterite .The agglomerates are generally 

 formed of more or less angular pieces of rocks ejected from the 

 volcanic vent, but in the one instance alluded to previously, there 

 occurs a bed at the base of the newer volcanic deposits, consisting of 

 rounded boulders or pebbles, mostly of small size, the origin of which 

 is not yet quite clear to me. These fragments might either have been 



