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" Pre-Jurassic Books. "These consist chiefly of dark-coloured sandstones, greywackes and slates, in which no fossils have as yet been found. The only rock belonging to this formation that I wish to notice is the so-called felsite at Waiohanga Point, north of Grahamstown. This rock was described by me in 1867 as a felsite tuff. Afterwards I called it a felstone, meaning thereby an altered eruptive rock. By Mr. E. H. Davis it was considered as a claystone 'cut through by a band of pyritous quartz sandstone.' Mr. S. H. Cox calls it a felsite, but is uncertain whether it is intrusive in or interbedded with the slate rocks. When I first visited the locality in 1867-69 the junction between the felsite and the blue slates was hidden by sand, but last year I found the sand washed away and the junction exposed. It could then be seen distinctly that the felsite was interbedded with the slates. Above the slates comes a bed of felsite 5 ft. thick, then 4 ft. of pale slates, and then the main body of the felsite which forms the Point. Both the blue slates and the white felsite are largely impregnated with pyrites in places, in other places they are free from it. The felsite is creamy white, with an earthy fracture and a hardness of about 3. It is irregularly jointed in three directions, and the joints are so numerous that it is difficult to get good specimens showing a fresh fracture. To the naked eye it is distinctly vesicular, the vesicles being minute and irregularly scattered. It is not laminated, but occasionally there are bands of a coarser material in it. Where it is vesicular there is no pyrites, and the vesicles are probably due to the removal of the latter. Under the microscope with an inch objective and ordinary light it is seen to be very finely granular, with minute specks of an opaque white mineral like leucoxene. In places there are rather sharply-defined clouds of lighter and darker, but no distinctly crystalline forms. Occasionally narrow pale bands run through it, in which larger masses of the opaque white mineral are collected. The vesicles are either rounded or angular, and are no doubt due to the decomposition of pyrites. With polarised light and crossed nicols the general tint is dark-grey, with bright specks; a few microlites can be seen, and more abundant anisotropic angular grains without polarisation colours. With an eighth objective it appears as a water-clear glass with minute rods and specks, and occasional layers of larger, irregularly-shaped, dark fragments. The quartz-sandstone of Mr. Davis has a microscopic structure similar to that of the felsite, but has, in addition, quartz grains scattered through it as well as abundant pyrites. The specific gravity of the felsite without pyrites is between 2-494 and 2505, and Mr. W. Skey has made the following partial analysis of it : Silica, 7346; alumina, 22-11; lime, 0-77; magnesia, 1-34; alkalies, 1-56; water, 0-76: total, 100-00. Mr. Cox has observed a similar rock interstratified with the slates of Coromandel (loc. cit., p. 7), and I am now convinced that this felsite is of clastic origin. It resembles a felstone in appearance, but is much softer and has an earthy fracture, while the small quantity of water contained in it forbids it being considered a slate or clay-stone. Perhaps it will be better to return to the name felsite-tuff which I originally gave it. " Post- Jurassic Bocks. "These cover the greater part of the Peninsula, and are almost entirely volcanic. At Coromandel and at Kennedy's Bay distinctly stratified scoraeaceous agglomerates are found which are the youngest rocks of the formation ; but elsewhere, so far as my observations go, there are no traces of stratification, no vesicular rocks, and different lava streams can rarely be distinguished ; volcanic breccias frequently occur, but they usually pass imperceptibly into unbrecciated rock. Hard dark rocks are comparatively rare ; usually they are light coloured —grey or greenish—and with a trachytic habitus, but soft. At Coromandel they were called trachytes by Dr. Yon Hochstetter, and this has apparently been confirmed by Mr. W. Skey, who found the alkali in them to be potash. (' Report on Geology of Thames Goldfields,' 1867, pp. 5, 6.) However, both at the Thames and Coromandel I have always found the felspars to be plagioclase, probably labradorite, or a still more basic variety. "When I first examined the district, twenty years ago, I was much puzzled with these volcanic rocks, for they were unlike anything I had seen before—indeed, their equivalents are found in Hungary, Transylvania, and North-west America. Seeing breccias and no vesicular lava-streams, I supposed that the whole series was an enormous mass of tuffs dipping slightly to the west or northwest, and traversed by dykes of timazite, melaphyre and dolerite, which looked very different from the surrounding rocks. As much of this supposed tuff was porphyritic, with glassy feldspar crystals, I supposed that these portions had been altered by heat. Five or six years later, having had more experience in acidic volcanic districts, I changed my views and considered these ' tuffs ' to be submarine lava-flows of viscous trachyte. (' Geology of the Thames Goldfields,' Trans. N.Z. Inst., 1878, Vol. vi.) Professor G. H. F. Ulrich, in a letter, informs me that many years ago he determined the hard black rocks occurring in patches among the light-coloured ones in the goldfields, as well as in the range just beyond its limits, as varieties of augite andesite, the former frequently containing hypersthene. Last year I made a collection of rocks from this formation, and selected out of it a series of twenty-eight, from which I made sixty-seven thin slices for microscopic examination. " Sedimentary Bocks. —The lowest beds of the auriferous series at the Thames are seen on the south side of Waiohanga Point, between the point and Waiohanga Creek. Here the high bluff of the point is formed by the felsite tuff already mentioned, and has a steep slope on the southern side. On it rests a white felsitic clastic rock with small round pebbles of the felsite tuff. Then comes a breccia of fragments of blue sandy slate in a sandstone matrix, which is composed chiefly of felsite grains, but also contains some quartz and a little chlorite. Upon this is a bed of sandstone, composed of the same materials as the last; and then follows another slate breccia which passes upwards into the andesite and andesitic breccias which compose the auriferous series. The exposure is not sufficiently clear to measure the thickness of these basement beds. A much better junction of the two formations is seen on the coast a few miles north of_Tapu, between the Mata and