a—9

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Towards the source of the Rangihau the rhyolites reach to the foot of Table Mountain, and more to the north of Table Mountain Range, at heights of 1,600 ft. to I,Booft. above the sea; but from the north-west side of the valley at Dirty Camp a narrow strip of acidic rocks, consisting of rhyolites and rhyolitic breccia, passes the north-eastern end of the Table Mountain Range, and, turning to the south-west, runs along the western slope of Table Mountain to the water-divide between the Waiwawa and Waiwawa Creek, falling into the Kauaeranga River. This area of acidic rocks within the Kauaeranga watershed comes in contact with the columnar intrusive rocks of Table Mountain, and, in all seeming probability, has been separated from the main area of the rhyolites east of Table Mountain by the appearance through them of the more basic rock. How this western tongue of the rhyolites is terminated in the upper valley of the Kauaeranga has not been definitely ascertained; but, ow 7 ing to the continuance to the south-east of the columnar intrusive rocks of Table Mountain, it is probable they do not rejoin the south continuations of the main area east of Table Mountain. On the saddle forming the parting between the Upper Waiwawa and Waiwawa Creek the rhyolite and rhyolitic tuff is exposed. Near the source of the Waiwawa Creek these are underlain by conglomerates composed mainly of volcanic rocks derived from the older groups, and these again by soft brown sandstones passing into or alternating with sandy shales and carbonaceous shales with thin seams of coal. In some places the finer of these beds resemble oil-shale;. the whole resting on rocks of the Beeson's Island group, constitute a series of considerable thickness, estimated at from 200 ft. to 300 ft. Unio aucklandicus is very abundant in some of these beds, where they are also crowded with plant-remains, and are generally of a dark colour owing to the presence of carbonaceous matter. The plants are similar to those collected from the sedimentary deposits in connection with the rhyolites on the east side of the Table Mountain Range. In the Waiwawa Creek the beds dip east at angles varying from 15° to 20°. This shows that considerable movements have taken place since they were deposited, and that they are of older date than the high-level deposits of the low grounds on the west side of the Peninsula, which are scarcely, if at all, disturbed. The rocks forming the area of the Acidic group on the east side of Table Mountain, and thence stretching south along the water-divide between the Kauaeranga and Tairua Valleys, are confined on its western side to the higher part of the mountain-range. Round the sources of the Hikuwai and the Second Branch of the Tairua the eastern boundary of the rhyolite, &c, is very irregular, owing to the manner in which these have been cut through, and the underlying rocks of the Kapanga group exposed along the bottom and sides of the many deep gorges and narrow valleys that intersect this part of the range. The acidic rocks are, however, continuous along the higher part of the range to the first peak north of the source of the Fourth Branch, and descend the range on the east side to within a mile of the Tairua River. Spherulite and dark pitchstone rocks having a perlitic structure are rocks of common occurrence on this part of the range. At the point where the Fourth Branch leaves the mountains the rhyolites appear in the low grounds of the Tairua Valley, and along the east bank to the Broken Hills gold-workings. On the west bank of the river the underlying rock is often exposed, as has already been described, and an irregular boundary is thus formed with the outcrops of the younger rocks adjacent. Along the lower slope of the range the acidic rocks are often deeply involved along lines of contact with the Neavesville breccias, which constitute the auriferous rocks at Broken Hills. On the west side of Broken Hills the contact is as near as may be vertical. East and south-east of Broken Hills the rocks of the Acidic group occupy a large extent of country between the Tairua Valley and the coast-line, and this, to some extent separated from the northern area, beginning at Mercury Bay, may be treated of separately. In the angle formed by the Hikuwai Stream and the Tairua River, below the junction of the two on Marsh's farm, there is an outcrop of glassy fluxion rhyolite in which common opal and opals of high quality are found. Excellent specimens of fire-opal are here obtained, and some of the stones of better quality are of considerable size. A quarry has been opened for the purpose of working the gem-bearing stone, but the methods in vogue at the time the place was visited last March were not such as should be practised with the aim of preserving the stones unbroken and entire. Many of the opal stones are without question valuable, but care will have to be exercised in obtaining the rough block, and skilful means employed in the extraction of the gems from these. From the upper to near the lower landing on the Tairua River, a distance of from five to six miles, the acidic rocks appear on both banks of the river, and, with the exception of a small area in the foothills opposite the island above the lower landing, and the possible presence of andesic rock in the sea-cliffs of the coast-range between the mouth of the Tairua River and the entrance to the Wharekawa River, and a small area of hard dark andesic rocks on the north bank of the Wharekawa, the whole country between the Tairua River, the coast-line to the south, and the Wharekawa River, is formed of rocks belonging to this group. Some distance below the line of travel, from Whangamata across the Tairua Valley, and the main range between the Omaha Puriri Streams in the Tairua Valley, the acidic rocks cross from the east to the west side, and thence reach on to the crest of the main water-divide at the source of the southern branch of the Puriri. Rhyolite is sparingly met with in the northern branch of the Puriri, and within the valley of this stream it has not been detected in situ. Rhyolite tuffs, glassy and earthy rhyolites, and great masses of grey earthy rocks of the same type, are met with between the upper part of the Wharekawa and the upper third of the mountain by which the track crosses the mam range from the Tairua to the low grounds of the Omaha Stream. The higher part of the range is formed of solid dark andesite, but, after making for some distance descent on the western side, rhyolite tuff again makes its appearance at a lower level, to be again followed by andesic rocks, and these again by solid rhyolite, forming Omaha Peak and extending south across the main valley of the stream into the Hikutaia watershed. In quite the low grounds of the Omaha Valley the rhyolites come in contact with the breccias of the Beeson'& Island group.