C.—3

6

sea-level. It is therefore clear that not west, but east, of the fault-line deep-sinking operations should be carried on, where a saving of from 1,000 ft. to 1,300 ft. of sinking, compared with any position taken up on the west side, would be effected. As it was, however, the Queen of Beauty shaft was decided upon, the influence of the Moanataiari Slide" not being taken into account. " But on whichever side of the fault-line a deep shaft may be put down, or boring operations carried on, there has to be considered the probability of such reaching another ' plank 'of country carrying payable gold. The venture must be regarded as somewhat risky, but considering the interests at stake much may be hazarded, and here it may be well to examine the evidence for and against a successful issue of such an undertaking. " An accumulation of clastic volcanic material, such as appears over the greater part of Cape Colville Peninsula, does not readily lend itself to the distinguishment of the exact superposition of the different deposits that have taken place, and the presence of sheets of lava between this can only be of very local assistance. Nevertheless, within limited areas something like a rude stratification can be made out, and the superposition of one mass upon another determined. Hence Hutton speaks of the upper and lower parts of the whole, and Cox refers to the Tararu Creek breccias as being at the base of the whole series of accumulations. Park also, in his section from Bonemill Creek to Hape Creek, indicates a like rude succession of the rocks; and, in spite of the obscurity of the section, I have little doubt that along Tararu Creek the lowest rocks are towards the west, and the highest towards the east, near the source of the creek; and in other parts of the district of Cape Colville the andesites, taken together, are followed by trachytic rocks, including rhyolite. Locally, such superposition is not difficult to determine, even when an inconsiderable thickness of rock is concerned, but over a wider field a greater thickness of rock has to be dealt with as a single stratum, and over the whole only the great groups of rocks can be considered as indicating such an arrangement. " It has been objected that I have dealt with the geology of Cape Colville Peninsula as though the volcanic rocks thereof were stratified deposits. If this has been so, I was quite unconscious of making any special effort in that direction ; but I necessarily noted superposition where it appeared in limited sections, and the succession of the larger masses of rock over a greater field. There is no real difference in the mode of accumulation of clays and sands on the one hand and coarser volcanic debris on the other ; and successive sheets of lava superimposed on each other are subject to the law of successive deposition, and it is only when molten masses are injected between former accumulations that this rule can be set aside. On the Thames Goldfield the general arrangement of the volcanic material indicates the lower beds in the west, and more narrowly examined the dips seem to be N.E., E., and S.E., the focus of such dip lines being a point in the Firth of Thames opposite Shortland. This may be taken to indicate the area immediately west of Shortland as the eruptive centre from whence the bulk of the material piled up to the eastward has emanated. As a matter of fact, this is a highly speculative conclusion ; and in passing it may be stated that centres of eruption are hardly anywhere determinable near the Thames, or, indeed, over the entire peninsula. The only evidences in this direction are a few hardened or coarse agglomerate cores and the presence of much sinterous matter, which may be presumed to have broken out on the flanks of volcanic cones once existent in the neighbourhood, but now, through denudation, not to be distinguished from the surrounding ash and lava fields. To the west of the Thames all such evidences have been eroded away or overflowed by the waters of the sea, and it is only in the Kauaeranga Valley and in the Look-out Eocks between the upper part of Tararu Creek, the source of Karaka Creek, and the Kauaeranga that such evidences are to be met with. To meet all the requirements of the case on the supposition that the old volcanic vent was situated three-quarters of a mile west of the shore of the Firth of Thames, opposite the Town of Shortland, or the mouth of Karaka Creek, a mountain 4,300 ft. in height was a necessity in order to unite in one even grade the western slope of the imaginary mountain with the Lookout Eocks and the sinterous quartz deposits of the Otonui Valley. Excepting one-third of the slope on the eastern side, and what lies below the longer slope from the Look-out Eocks to the Firth of Thames, this mountain has been wholly removed to, and to a considerable distance below, sea-level; but while it yet had considerable mass the processes by which fissures were formed and filled with auriferous quartz must have been going on and were completed before the fracture and displacement constituting the Moanataiari Fault was formed, there being no fissures filled with reef-matter crossing this. "After the volcano as such became extinct, thermal action continued for a long time, and there is evidence that the mountain had been considerably reduced in height and mass before the sinter deposits of the first northern tributary of the Kauaeranga were deposited. These, however, were probably the, latest deposits of their kind, and post-date the formation of many of the reefs. "By what process the reefs were formed, and whence was derived the gold now found in them, is necessarily a matter of speculation. As sensible, though minute, traces of gold are found in the solid and less-decomposed rocks of the Thames Goldfield, even at considerable distances from the reefs that traverse them, it has been thought the erupted rocks themselves are the source of the gold, and that the alterations which have taken place, ending in the production of the grey decomposed form of andesite—often described as propolyte, and as frequently called the sandstone of the miner—favoured the leaching of a portion of their silica from the rocks, and at the same time most of the contained gold, which eventually was deposited in the form of auriferous reefs in fissures previously existing, or widening and formed at the time of deposit. This action could scarcely have been set in motion and carried on by the mere access of superficial waters; and, as the rock alteration continues to a great and unknown depth, ascertained to be at least 750 ft. below sea-leval, thermal waters, no matter what their source, must be considered as largely responsible for the results.