Geological Features.

Banks Peninsular, an extinct volcanic system of large dimensions, standing as an island, in post-pliocene times, in the sea, shows by the configuration of its base that an oscillation averaging about 20 feet in vertical height has taken place, the country being depressed and afterwards raised to about the same altitude again. This line is well visible travelling round Banks Peninsula to its western termination, where, when we reach that altitude above the sea level, the signs of a former submersion disappear below the newer fluvia-tile and lacustrine deposits.

During and after the small submergence of its base, this portion of Banks Peninsula was of course subjected to the fury of the waves, when in favourable localities caves were formed, either by the removal of loose material (tufas) between two harder lava streams, or by the enlargement of pre-existing hollows, such as are found as air bubbles, often of gigantic size, in lava streams running generally parallel to the direction of their flow.

In this instance there is no doubt that the Moa-bone Point Cave is a pre-existing hollow in a doleritic lava stream, which has been enlarged by the enormous power of the dashing waves of the ocean beating here at one time furiously against the northern foot of the Peninsula.

In previous publications (amongst others, “Report on the Formation of the Canterbury Plains, 1864,” page 22, et seq.) I have shewn how in post-pliocene times from the material brought down by the enormous glacier torrents, forming huge shingle fans at the foot of the glaciers, two bars were thrown across the sea; one to unite the northern, or Waimakariri-Ashley deposits, with the northern slopes; another to connect the southern or Rakaia-Ashburton beds of the same nature with the southern slopes of Banks Peninsula, behind which a huge lake was formed, of which Lake Ellesmere is the last remnant. Of the northern bar we can trace the inner or western shores through Kaiapoi to the neighbourhood of Woodend.

In this large fresh-water lagoon (occasionally an estuary basin) the Waimakariri, Selwyn, and sometimes the Rakaia discharged their waters, having an outlet near the north-western slopes of Banks Peninsula, of which, in going towards Cashmere, the residence of Sir Cracroft Wilson, we can easily trace the lines of dunes and shingle by which the eastern shore of that lake was formed, being in the beginning very narrow, and only gradually, as more and more material was added, assuming a greater breadth. Thus we are able to follow the different lines of these earliest-formed beds from the neighbourhood