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their free-milling bullion is alloyed with silver to the extent of about 30 per cent., as it is throughout the Hauraki Peninsula. ' Palceozoic Bocks. —These form the basement or floor of this district, and, indeed, of the whole Peninsula. They consist principally of hard siliceous, greenish, and grey-coloured sandstones, interbedded with slaty breccias, and occasionally with slaty shales. The siliceous sandstones or greywackes are the prevailing rock here. They are very much shattered and jointed, and often streaked with thread-like veins of quartz or haematite. On the spurs behind the township, and in most places near the point of contact with the overlying tuffs, they are decomposed into reddish-coloured clays to a great depth, as if they had been subjected at some period to the long-continued action of thermal waters. The gold-bearing reefs of this formation are found in the more decomposed portions of these sandstones, and the quartz is often of a brecciated, flinty, or chalcedonic character, which is an evidence of hydro-thermal origin. These rocks have yielded no fossil remains, and their exact age is therefore still undetermined ; but in the Waikato they have been found underlying rocks which contain Halobia monotis, and other Triassic forms, and hence have been placed in the Palaeozoic Period. ' Gold-bearing Beefs. —I have already pointed out that there are two distinct reef-systems at Kuaotunu, one belonging to the tuff formation, and the other to the Palaeozoic formation. The major lode of the field is the Try Fluke Reef, found in the former. It possesses well-defined walls, and varies in width from 2 ft. to 20 ft. Its average width is probably about 6 ft. Its course is north-north-east, south-south-west, and its dip easterly, at angles seldom under 60 degrees, more often over 65 degrees. It has been traced through the leases of the Kaipai, Try Fluke, Carbine, Red Mercury, Great Mercury, and Irene. It has been proved to continue downwards in the deepest workings so far undertaken upon it. All the workings on this reef have, so far, been confined to the brown oxidized tuffs above water-level. The nature of the quartz varies in different parts of the lode. In places it is hard, cavernous, and stained black with manganese oxides ; in others it is mullocky, and more friable or crumbling, and is stained rusty-brown with peroxide of iron. The gold is alloyed with about 30 per cent, of silver, and it exists principally in an extremely finely divided state. The patches of rich stone, which are so characteristic of the Thames reefs, are not known in this reef, or, indeed, in any other reef in this field. The reefs in the Palaeozoic sandstones have received a large amount of attention, and most encouraging results have been obtained from the Blackjack and many others. ' There are no known laws regulating the distribution of gold, although some geological conditions are known from experience to favour the occurrence of gold more than others. It is therefore impossible for any one to predict with any degree of certainty where gold may or may not be found in paying quantities. At Tapu and Coromandel it is found that when the reefs descend from the tuffs to the Palaeozoic rocks they run out, or become non-gold-bearing. At these places the old rock consists of black jointed slaty shales. At Kuaotunu they consist of siliceous sandstones, and the prospects of the permanency of the reefs in them are altogether more favourable. At the same time, it would be wrong to neglect the experience of other places; and in the case of Kuaotunu, it would, I think, be prudent to thoroughly prospect the reefs before undertaking the erection of batteries and other expensive works. Up to the present time the Try Fluke reef has proved the chief gold-producer on this field, and, so far as can be judged from the existing conditions, it seems likely to hold this position for a number of years to come ; but to effect this, low levels will have to be driven in most of the mines on its course. With the advent of a cheaper motive-power many reefs that at present would not pay to develop could be worked with profitable results, and there would then exist a fresh incentive to undertake systematic prospecting in new directions, which would no doubt result in other discoveries of a valuable nature.' " * In the first volume of the " Transactions of the Australian Association for the Advancement of Science" (Sydney meeting, 1887) is a paper by Professor Hutton, "On the Rocks of the Hauraki Goldfields." Such parts of this as deal with the general geology of the Peninsula or particular parts of it are here transcribed, giving the writer's latest views on the subject. Professor Hutton introduces his subject as follows : — "The Hauraki gold-mining district, Auckland, New Zealand, extends from Cape Colville on the north to Te Aroha on the south, a distance of about one hundred miles, and includes the subdistricts of Coromandel, Tapu, Thames, Ohinemuri, and Te Aroha. In geological structure it consists of a sedimentary formation of slates and sandstones, not younger than Triassic, overlain quite unconformably by a Younger formation chiefly of volcanic origin, which is not older than Cretaceous, and in which all the gold-mines are situated. To this statement all geologists are now agreed, but opinions differ as to whether any long interval of time separates the volcanic rocks into two distinct series, the older of which is alone auriferous, or whether all should be considered as parts of one. This point will not be decided until the country in the neighbourhood of Cabbage Bay is satisfactorily made out. In this district the limestones of Oligocene age containing Hemipatagus tuberculatus, Pentacrinus stellatus, Ostrea wullerstorfii (?), as well as Fusus, Turritella, Gucullcea, and other genera, are found in close proximity to the auriferous volcanic series ; but the officers of the Geological Survey who have reported on the district hold diametrically opposite opinions as to its structure. If Mr. S. H. Cox is right in supposing that these limestones, &c, rest unconformably on the auriferous series (Reports, Geological Explorations, 1882, page 19), then that series will probably be Cretaceous, and the volcanic rocks of Coromandel and Kennedy's Bay may be much younger. If, however, Mr. A. McKay should be right in saying that the auriferous volcanic series lies unconformably on the sedimentary series (Reports, Geographical Explorations, 1885, page 98, &c), then the whole volcanic formation must be considered as not older than Miocene.

* Mines Reports, 1893, pp. 93, 94.