61

c—d

south headland of Cabbage' Bay, and on the coast for a short distance to the south, and consist of a coarse breccia of loosely-cemented material, usually of a light-grey colour, coarsely crystalline, the felspars predominating. South of Cabbage Bay solid floes of grey porphyritic andesite, having a sub-columnar structure, appear on the coast-line, and darker augitic rocks appear in the south-east part of the area immediately overlying the coal-bearing beds of Torihine and Tawhetarangi Creek, and separates these from outcrops of the same rock in the west branch of the Umangawha River. In the report of December, 1883, I divided these rocks into three divisions, the lower of which I seem to have regarded the equivalents of the Kapanga group, as this is seen in the ranges on the east side of the Umangawha Valley. Furtherresearch has shown that the rocks on the two sides of the valley are not the same. In the southern part of this area the boundary between these and the rocks of the Kapanga group is not easily determined. As in the southern source of the west branch of the Umangawha, the rocks of the coast-line north of Torehine appear as dyke-like masses, and apparently extend south through the range intervening to the new road from Coromandel to Cabbage Bay, and the boundary may be more to the south and east of where it appears to be on the map accompanying. This, however, is a matter of secondary importance at the present time. None of these rocks within this area are auriferous, and they are highly unconformable to those of the Kapanga group, as developed on the east side of the Umangawha Valley. It is the evident unconformity of the Beeson's Island rocks at Cabbage Bay to those of the Kapanga group in the northern part of the Tokatea Range, and in the Cabbage Bay Range east of the Umangawha Valley, that makes them of importance. It might be difficult to prove unconformity between the two in the district around Coromandel Harbour or further south, or on the East Coast from Stony Bay to Mercury Bay, but fortunately at Cabbage Bay the unconformable relations of the two are quite apparent. As the Kapanga group consists mainly of fragmental ejectamenta accumulated on Austral Hill .and the Cabbage Bay Range to the depth of 1,000 ft. or more, and forms a very abrupt slope on the east side of the valley down to 800 ft. and 600 ft. above the level of the sea, below which level into the low grounds of the valley slates are met with, it is clear from the nature of the material and the mode of their deposition that the rocks of the Kapanga group must have been spread over the district to the west, and might be expected to occur interposed between the Beeson's Island rocks and the coal-measures or the slates. They are absent, and are absent due to their having been removed by denudation prior to the deposit of any of the rocks forming the Beeson's Island group. The slates and coal-measures were thus laid bare, and, subsequently, from a volcanic centre lying to the west of the coast-line the rocks of the Beeson's Island group were discharged, and . built up the superimposed lava-streams, breccia, and ash-beds by which the group is here represented. Without question, the Beeson's Island rocks were at one time in contact with those of the Kapanga group throughout the Umangawha Valley ; but except in the south these rocks have been carried away, and along the middle and lower course of the river they are now confined to the west side of the valley, reaching to sea-level. On the opposite, the east side of the valley, from above the slates, spring nearly vertical cliffs of Kapanga rocks, directly opposite where the younger series reaches furthest into the low grounds, and for a short distance on to the east side of the valley. The relations of the two groups, and the evidences of the unconformity between them, is shown in the section from Torehine to Kennedy Bay section. On the north-west slopes of Moehau these beds were not particularly examined, but according to Mr. Park, who during the past summer examined the coast-line of this part, the rocks are for the most part hard grey porphyritic andesites of an intrusive character that extend to the north, to the west side of Port Jackson. South of Port Jackson, over the eastern part of this area, the rocks are of a less intrusive character. From Stony Bay to Port Charles the rocks belonging to the Beeson's Island group are, in the main, coarse breccias, the larger blocks in which are usually dark augitic andesites, and, where of finer material, greenish or grey, nests and veins of calcspar being not uncommon. On the east side of Port Charles these breccias are of a very coarse description, blocks 6 ft. or 8 ft. in diameter being not uncommon. Further south along the coast-line finer-grained breccia and ash-beds are plentiful, but in the hills more to the east enormously coarse breccias are met with. In this part lava-streams having a more or less perfect columnar structure cap the finer-grained breccia and ash-beds, and at places curiously display in the same lava-stream vertical and inclined columnar structure. The coast-line of this part is high and precipitous, and inland the hills are high, and form rugged broken country. The boundary between these and the Kapanga rocks is fairly well marked in the valley of the creek falling into Big Sandy Bay, and in that of the main stream falling into the upper part of Port Charles, but over the broken country to the mouth of Waikawau Creek it has not been followed. On the opposite (south) side of the bay, into which Waikawau Creek discharges, the boundary between these and the Kapanga rocks is well marked, and to the south the Beeson's Island rocks continue along the coast-line and inland to the slate country extending north from the inner part of Kennedy Bay. East of the slates, and forming the north head of Kennedy Bay and the neighbouring hills, the rocks of this group resemble closely those of the typical locality, Beeson's Island, and the south shores of Coromandel Harbour. The lower part of the group on the north side of Kennedy Bay consists of solid floes of grey rock resembling trachyte. The upper part is a very coarse breccia of light-grey colour; that on the shore-line has weathered into a variety of fantastic shapes. On the hill-slopes the breccias are of large size, and full of fissures and caves that in times past have been used as places of sepulture by the. Maoris. The same beds occupy the whole of the south side of the bay. The solid rocks forming the lower part of the group appear at the head of the bay, and here occurs a remarkable stratum, the lower part of a lava-stream, having a structure that closely resembles that of mica-schist. The formation extends inland towards the Tokatea Range for about a mile from the head of the bay, and forms the crest of a high conical hill on the south side of the valley leading forward to the foot of Tokatea Hill.