of formation of the great hollows or calderas now occupied by Lyttelton and Akaroa harbours. It will be readily recognised that these authorities are in substantial agreement among themselves and with the present author in regarding the major land-forms, including the calderas, as the result of the erosive action of streams on the interior of the craters and the exterior slopes of the two volcanic cones, this action having been initiated and continued when the land stood at a higher level than at present.

Since the Akaroa volcano shows little departure from the simple and regular structure of a single composite cone, the present form of the central hollow may well be used as the type of an erosion caldera in an early mature stage of development, and in the opinion of the author it has been formed in the following manner. One of the streams on the exterior slope of the cone was favoured by some accidental factor, such as (1) a moderate summit explosion which resulted in the break-down of a portion of the crater-ring, or (2) a higher intensity of rainfall over one sector. In consequence the stream was able to break into the crateral hollow from the outside, take to itself the interior drainage, become the dominant or master stream, and enlarge its head to an amphitheatre form by the headward and lateral erosion of tributaries converging towards the centre of the basin. When subsidence of the land took place the sea invaded the hollow and formed the present harbour. Some of the streams on the exterior slope, such as those occupying the Little River and Pigeon Bay valleys, also enlarged their heads so that they simulate a caldera form, not only in their upper reaches, but also in their cliff-guarded entrances; but up to the present they have not succeeded in breaking into the enlarged crater. When the land was lowered the sea occupied the lower reaches of the valleys and formed the fringe of bays round the present coastline. The distal ends of the spurs dividing the bays have been exposed to heavy seas, and have been cut back into bold cliffs, notably when the land stood at a higher level; a subordinate amount of cutting has taken place at about present sea-level.

The erosion pattern of Lyttelton has been carried a stage further as it is the older volcano of the two. The crater-ring has been broken in two places, and the narrowness of the summit ridge at the head of some of the exterior valleys, as for example that of Heathcote Valley, foretells the location of future breaks in the ring. There are other signs as well, such as the presence of planezes, which indicate a more mature stage of erosion than is shown by Akaroa. Although bold cliffs mark the coast near the entrance to Lyttelton Harbour, and also near Sumner and Redcliffs, the spur-ends of the remainder of the periphery are not so distinguished. This absence is no doubt due to the more sheltered position of the western stretch of coastline when the peninsula was an island, and any cliffs then cut are now masked by the subsequent lowering of the land and by the material brought down by the Canterbury rivers and deposited along the western fringe of the eroded cone.

Finally, in making a comparison between these two calderas and that of Carnley in the Auckland Islands, it should be noted that the second break into the craterial hollow of the last is to be credited