496 Transactions. — Geology. 



deep indentations, forming splendid harbours, enter far into the outer rim 

 of the mountains, passing for a considerable distance along the higher 

 central range. Similar indentations are also found to exist towards the 

 Canterbury plains, but they have either been already filled by alluvial 

 deposits forming fertile valleys, such as the Kaituna valley, or they appear 

 in the form of a lake (Lake Forsyth). In examining the nature of the rocks 

 of which the system under consideration is composed, we find that, with 

 the exception of a small zone at the head of Lyttelton Harbour, the whole 

 is composed of volcanic rocks ; that the deep indentations are ancient crater 

 walls, so-called calderas, into which a channel with precipitous walls, the 

 barranco, leads ; and tliat they consist of a series of lava streams, with 

 agglomerates consisting of scori®, lapilli, ashes, and tufas interstratified 

 with them. These beds have all a qua-qua versal dip, that is to say, they 

 all incline outwards from the centre of the cavity. The higher mountains 

 in the centre consist also of volcanic rocks of a similar composition, which 

 appear either horizontal or, when the direction of the lava-streams com- 

 posing them can be ascertained, are found to flow into the calderas 

 previously formed, from which we can at once conclude that they are of 

 younger origin. Finally, we find mostly in or near the centre of these deep 

 cavities, or calderas, either a small island or a peninsula stretching so far 

 into these harbours. They consist also of volcanic rocks, having been 

 preserved above the last centre of eruption. This last sign of vulcanicity is 

 on a smaller scale than the previous ones. The whole of Banks Peninsula, 

 measuring along its longest axis from north-west to south-east, has a length 

 of 31 miles, with a greatest breadth of 20 miles, and if we do not take the 

 numerous indentations into account, it has a circumference of 88 miles, 

 which corresponds closely with that of the base of Mount Etna. 



Having thus given an outline of the general features of the volcanic 

 system under consideration, I shall now proceed to offer a short history of 

 its origin. 



The oldest rocks in Banks Peninsula form a small zone of palaeozoic 

 sedimentary strata, possessing a slightly altered -structure, many of them 

 forming beds of chert, others, peculiar light-coloured brecciated schists ; 

 however, sandstones and dark clay-slates are also re|)resented. This zone 

 has a north and south direction, and reaches to the southern watershed of 

 McQueen's Pass, which leads from the head of Lyttelton Harbour to Lake 

 Ellesmere. Near this pass, slates appear as high as 600 feet above the 

 sea-level. On the western slopes of Castle Hill, the south-western cotinua- 

 tion of Mount Herbert, 2,900 feet high, which rises so conspicuously above 

 Lyttelton Harbour, they reach an altitude of nearly 1,000 feet, where they 

 are overlaid by the older lavas, forming the Lyttelton Harbour caldera. 



