344 Geology of 



lock, but sometimes a little different from that obtained in the 

 former, it being more silky in appearance and containing more 

 olivine. When porphyrinic, the crystals of labradorite and augite are 

 well formed ; the scoriaceous lava is not so porphyritic, and has 

 generally a reddish colour. Most of the ashbeds are also different, 

 being of greater thickness before they alter to agglomerates, and 

 having a peculiar chocolate purple colour. Only one other similar bed 

 is found in the Lyttelton caldera, at Quail Island, the last centre 

 of eruption. The tufaceous beds contain sometimes small portions of 

 wood, so much altered as to assume a nearly anthracitic character. 

 Iron pyrites (marcasite) has also been found in the same deposits. 

 Most of the secondary minerals examined from the Lyttelton caldera 

 have also been collected in Akaroa Harbour Another distinguishing 

 feature in this harbour is the preservation of a portion of the sides o£ 

 the old crater, which reaches to the very centre of the volcanic vent, 

 from which the whole caldera wall around ifc has been built up. This 

 portion forms a peninsula, owing doubtless its preservation to the 

 existence — if I might thus express myself — of a core of a peculiarly 

 hard lava, which has been found nowhere else in Banks' Peninsula, 

 consisting of a very granitoid trachyte, containing crystals of quartz 

 and sanidine, and forming at the southernmost point of the Akaroa 

 Peninsula a hill several hundred feet high. Between this hill, which 

 in former times was crowned by a strongly fortified Native pa, and 

 the caldera wall, a succession of tufaceous and agglomerate beds, 

 mostly of reddish-brown or purple tints, have been preserved, and, 

 as it is perfectly evident, have repeatedly undergone great changes. 

 They are intersected by numerous dykes belonging to two systems, of 

 which one consists of doinitic rocks, running mostly from north-west to 

 south-east, the other of basaltic rocks having generally a south-west 

 and north-east direction. They are generally not quite vertical, and 

 have sometimes a slightly tortuous course. Beautiful sections of the 

 innumerable lava-streams and the agglomeratic and other beds of 

 -similar origin of which this system has been built up can be obtained 

 all around Akaroa Harbour and in the barranco leading into it. The 

 walls of this caldera have an average altitude of 2500 feet, rising in 

 Saddle mountain to 2750 feet above the sea-level. Below that moun- 

 tain a portion of the older caldera wall of the Little River vent is 

 hidden ; the Devil's Peak, 2050 feet high, lying to the south-west of 

 the former mountain, being doubtless a remnant of the latter 

 system. 



