Mr. A. McKay exhibited and described a large collection of rocks and minerals, collected by him during the past two years from the Cape Colville Peninsula.
After sketching rapidly the geology of the district, he proceeded to describe the more important features of the collection. The andesitic rocks of the Tokatea Range, the Thames, and Karangahake were compared to show their general correspondence, and those of Kaipanga and Kleven's Point, Coromandel, with the rocks of Maresville, Waitekauri, and Waihi. The Beeson's Island rocks were shown to be distinct, and present over a very large area of the southern goldfields of the district. The acidic rocks of the peninsula were shown to be largely developed along the east coast, south of Mercury Bay, and to occupy nearly the whole of the Upper Ohinemuri or Waihi Plain. Many samples of different kinds of quarts were exhibited, in evidence, it was claimed, that most of the reefs had been deposited by hydrothermal action, and in support of this cases were cited in which reefs of crystalline quartz could be traced until they passed into undoubted geyser deposits accumulated on the present surface of rocks of late Miocene age of the Beeson's Island group.
Sir James Hector said that Mr. McKay's magnificent series of rock specimens from the Cape Colville district would greatly increase our knowledge of this important goldfield. Even a superficial inspection of such large specimens would enable the cabinet student to acquire a better notion of the field geology than could usually be obtained from ordinary hand specimens. Large blocks also permitted of a much better selection being made for microscopic and chemical study. He did not altogether agree with the introduction of the terms “sphirulite” and “pearlite” as distinctive characters, seeing that they were structural forms of a variety of rocks. A most important point was mooted by Mr. McKay. All geologists were agreed that besides a core of ancient rock there were several succeeding series of igneous rocks belonging to widely different geological periods. As in other parts of the world, the core had formed the anvil against which the later-formed rocks were crushed, faulted, and impregnated with mineral veins. The last outbursts were certainly rhyolites, and if the suggestion that these were auriferous was correct it was difficult to see why goldfields should not extend overmuch larger areas of the North Island than yet discovered. Of course, the transfusion of the gold into rhyolite from the underlying rocks by solfatara action would account for local impregnations; but if the formation of the reefs took place after the date of the rhyolite outbursts, which seemed to be the author's contention, that was a novel idea that would requite full discussion after the true nature of the rocks had been obtained by experts. Mr. McKay had done the most laborious part of the work in collecting ample material in a most thorough manner.
The Chairman thanked Mr. McKay for exhibiting these interesting specimens, and for his explanation as to their nature and the character of the geological district from which they were collected. If the hydrothermal action in the formation of gold was proved it would settle a most-important question.
Third Meeting: 17th August, 1898.
Mr. E. Tregear, President, in the chair.
New Member.—Mr. J. Singer.
Paper.—On “Volcanoes of the Pacific,” by. Coleman Phillips. (Transactions, p. 510.)
The Chairman, in inviting discussion, said the dates of the eruptions mentioned should be given before we could determine whether they were
connected with the movements in New Zealand. He did not see how the coral-reefs referred to could help us, in the manner suggested, to form our breakwaters.
Sir James Hector, in response to the President's request, said he was glad that the author had commenced the important work of collecting and placing on permanent record the changes now taking place in the Pacific Ocean, it was the largest area of the earth's surface covered by ocean, and volcanic forces were active in many parts of it, but whether they were sporadic or along defined lines due to structural features in the underlying earth's crust had yet to be determined. He was therefore glad that a start had been made by the author of the paper to collect the ephemeral records on the subject.