836 Transactions. — Geology. 



would be at that time, in all probability, that the great fissure, 

 or fracture in the earth's surface, was first formed, or re-opened, 

 and a period of great volcanic activity set in, which has con- 

 tinued in a decreasing degree to the present time. 



The islands being wholly volcanic, we cannot expect the 

 assistance of fossils in determining their age. It seems unlikely 

 that any such should be found so near volcanic rents ; but I wish 

 to mention — more as a hint to future visitors than anything 

 else — that Mr. Bell told me he had found a fossil kukuroroa, or 

 great mussel of New Zealand, embedded in a mass of pumiceous 

 tuff which had fallen from the cliffs on the east coast of Sunday 

 Island. The finding was related with such circumstantiality 

 that I can scarce doubt the fact, though I searched half a day 

 in the locality without seeing anything of it. 



In stating that the islands date from Eocene times, it should 

 be understood that this was the age when tbe volcanic forces 

 first commenced to build up on the sea bottom the mountains 

 we now see. Their present shapes are due to much later move- 

 ments : indeed, some of the surface indications go to prove that 

 alterations have taken place in comparatively quite recent times. 

 Doubtless the first outburst must have been submarine, and 

 ages would elapse before the mountains appeared above the sea- 

 level. 



On Sunday Island — which is somewhat triangular in shape 

 and about 20 miles in circumference — we can trace a great deal 

 of the method by which it has been built up. All round the 

 island, except on the north side, can be seen very distinctly a 

 series of lava flows, composed of black and dark-brown andesitic 

 rock, all of which lie nearly horizontally. Separating these 

 flows in a great number of places are bands of red laterite, vary- 

 ing from a few inches up to several feet in width. These bands 

 are interesting as proving that the outbursts of lava were inter- 

 mittent, and that a sufficient time elapsed between each for land 

 surfaces to form and vegetation to flourish, to be destroyed by 

 the following overflow, and by it to be converted into the laterite 

 we now see. On the northern side the lava flows are hidden by 

 later deposits, which have extended outside them. The rents 

 from which these horizontal lava streams exuded are lost. They 

 probably originated when the island was of larger extent, for I 

 do not think they emanated from the craters whose remains 

 can still be seen. Resting on top of these lavas, somewhat 

 irregularly, are beds of pumiceous tuff of great depth, which are 

 composed principally of a dark coloured pumice, fragments of 

 andesite, obsidian, and other rocks. It is difficult to say whether 

 the whole of these tuft's are the product of the existing craters, 

 but I think not ; they are more likely to have been deposited 

 previously to the formation of the craters, which have since 

 burst through them. 



