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basic solutions were decomposed and their metallic contents electro-deposited, the base metals and a portion of the silver as sulphides, and the gold, together with the greater portion of the silver, as a metallic alloy. The formation of the quartz and the deposition of the metals was thus carried on simultaneously in the fissures by reactions, which were the complements of each other. During this period of solfatara action, and for a long time after, the dry land was ever subject to the denuding and degrading agencies of rain and running water. The present valleys were then being excavated, and the waste transported to the sea, where it was spread out on the floor by the sorting action of the water. " Since the second great outburst recorded above, which culminated in the formation of the massive trachytic mountains which occupy the higher and more inland portions of the Peninsula, as well as the outlying islands in Coromandel Harbour, this area has enjoyed complete repose from all volcanic manifestations. But not so in other parts of this island. In Newer Pliocene times the central portion of this island became the scene of the most widespread and devastating eruptions that have ever taken place in New Zealand. The region from Ruapehu to Tauranga was occupied by a chain of great crater-lakes filled with molten magmas, from which liquid streams of fiery acid lavas were projected over the country for hundred of square miles. At this time were formed Ruapehu, Tongariro, Pihanga, Tauhara, Horohoro, and the solfatara scarred mountains of the Tarawera region. The light frothy ash or pumice of the acid eruptions, either wind- or waterborne, was spread as a continuous sheet over half of the island. At Shortland the pumice deposit is only 10 ft. thick ; but in the Upper Thames Valley, and in the Upper Waikato, it is often found hundreds of feet deep, especially near the centres of eruption. The solid rhyolites, often much brecciated, reached as far north as Paeroa, Awaroa, and Waihi, filling in and levelling the old valleys excavated in the older volcanic rocks. Thus, at Waihi we find the well-known Martha Hill and its productive lode surrounded by a great thickness of grey rhyolitic breccias and lavas, which appear to have originated in the direction of Tauranga. " It was probably during these Pliocene eruptions that the great earth-movements took place which resulted in the formation of the faults which traverse the Thames Goldfield. These faults cross the lines of the reef systems transversely, and their courses approximate to the direction of the initial line of eruption, which no doubt followed the line of least resistance." * Description of the Different Formations occurring on the Cape Colville Peninsula. Considering the extent of the area examined and the rugged character of the Peninsula, and having regard also to the fact that much of its area has been till now geologically unexplored, it will be readily understood that nothing like a minute and exhaustive examination could be undertaken. All that was aimed at during the past season was a knowledge of the sequence of the different sedimentary formations and groups of volcanic rocks, and approximately to ascertain the areas over which each of these appear at the surface; to determine if possible the conditions under which the volcanic series had been accumulated, whether as the products of submarine or terrestrial volcanoes, and in which of them reefs or lodes carrying gold and silver in payable quantities occurred. This work has been so far effected as to enable the drawing up of the Table of Formations appearing on this page and the descriptions which follow. The scheme of classification includes divisions of the volcanic series not hitherto recognised by other writers on the geology of the Peninsula, and may in some cases be considered unnecessary; but I am fully convinced that in the field the distinctions made can in most cases be readily followed ; besides which in every case there is a chronological reason for the separation of the different groups, this being the unconformable relations that subsist between them. It is not denied but that some modifications of the mapping of the different boundaries may be necessary; this is to be expected, but on the whole the sequence of the different groups, and approximately, the areas assigned to them will be found fairly correct. Despite the difficulties in the way of this first attempt to describe the geology of the whole of the Peninsula, it is hoped that a body of facts has been brought together such as will serve the purpose for which the work was undertaken, and afford valuable insight to the structure of the Peninsula as a whole, and also be of value as regards particular localities.

Table of Formations.

Probable Age. Name oi Formation or Group. Characteristic Bocks. 8. Carboniferous .. Maitai Series Slaty breccias, grits, sandstones, siliceous and argillaceous mudstones, often calcareous, carbonised plants, and thin seams of impure coal. Conglomerates, sands, clays, and limestones with coal. 7. Cretaceo-tertiary Coal formation 6. ? Thames-Tokatea Group Volcanic ejectamenta, mainly andesic, solid fragmental or tufaceous, with traces of coal. Volcanic ejectamenta, mainly andesie, solid fragmental or tufaceous, with traces of coal. Volcanic ejectamenta, mainly andesic, in places trachytic, solid fragmental or tufaceous, with sedimentary deposits and seams of coal. Volcanic ejectamenta ; trachytes, rhyolites, porlite, spherulite, obsidian, &c, solid or tufaceous, with sedimentary beds and traces of coal. 5. Older Tertiary .. Kapanga Group 4. Miocene Beeson's Island Group 3. Older Pliocene .. Acidic Group 2. Newer Pliocene or Pleistocene Kauaeranga beds .. Grey sandy beds and ferruginous clays. 1. Becent Becent deposits Various kinds of deposit, from coarse beach or river shingle to pumice sand and clays. Dyke intrusions and thermal-spring deposits. * Mines Be' >orts, 1894 : Re; iort b James Park, i. 52 to 68.