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dykes of crystalline volcanic rocks, decomposed, or but little altered. The colours of the fragmental rocks vary from whitish through light-grey to dark or greenish grey and not un frequently in surface exposures are of a brownish tint. When solid and crystalline the rocks are of various shades of grey to almost black, according as the different minerals felspar, hornblende, or augite prevail or predominate. Numerous samples of these rocks were collected from the Coromandel district illustrative of their characteristics, but these have yet to be critically examined. And, for reasons given in the report dealing with the silver-bearing lodes of the Great Barrier Island, they shall be here spoken of as light- and dark-grey andesites, with accompanying breccia ash and tufa beds of the same character; and this will apply to the rocks not only of the Thames-Tokatea group, but to those of the Kapanga and Beeson's Island groups as well. Thames to Coromandel Area. —ln the northern part of the Peninsula the group of rocks under description begins on the eastern side of the Tokatea Range, between the slate hills inland of the upper part of Kennedy Bay and the Tokatea Range north of the Triumph Mine. At first they are confined to the lower slopes on this side of the range, but gradually they rise higher on to the range, till at the Triumph Mine they have passed the crest, and appear on the western side of the ridge. From the Triumph Mine the western boundary trends south along the west slope of the range to a little below the Pigmy Mine, in the valley of Mountain Hotel Creek, towards the northern end of the Success Range. From this point the west boundary is along the slopes of the Success Range to the point where the slates disappear, and a thin seam of coal shows at 580 ft. above sea-level. From this point the west boundary trends more to the south-east, and crossing a deep gully is again met with on the west side of the Tiki Range at a height of 650 ft. Thence the boundary is continued nearly in a straight line across the intervening valleys to the saddle on the Tiki Spur, where the lowest beds of the group are seen resting on rocks belonging to the Maitai series at about 800 ft. above the sea. From this point the west boundary of the Thames-Tokatea rocks trends more to the south and south-south-west, and reaches into the lower grounds along the east side of the Waiau Valley where they are overlain by rocks of the Kapanga series, the slates being no longer visible. At the point where the road turns to the eastward to lead on to the saddle by which the road to Mercury Bay crosses to the east side of the range, the rocks belong to the Kapanga group, but shortly the rocks of the group under description appear in the road-cuttings, and thence are continuous for several miles in an east and south-east direction. From this point the line of the eastern limit of these rocks, where it crosses the different source branches of the Manaia River, has not been exactly determined. This was due to the exceedingly rugged nature of the country in that part; but approximately the boundary is as shown on the map accompanying this report, till reaching into the Waikawau watershed, where the boundary is again determinable, and, further south, is seen in the Mata Valley at a point less than two miles inland from the sea. From the Mata Valley the boundary runs across the intervening hills to the Tapu Gorge, and thence returns to the north as far as the mouth of the Mata, leaving a narrow strip of these rocks between the slate hills and the shore of the gulf. From Mata Creek to Rocky Point, near the Thames, the shore of the Gulf and Frith of Thames forms the visible boundary of these rocks. The Shortland Flat and the high-level deposits of Irishtown and Mount Pleasant, at the western base of Una Hill, do but obscure these rocks, which at deep levels extend to beyond Hape Creek and probably reach as far as the bridge on the main road crossing the Kauaeranga River. The eastern boundary of this, by far the greater area of the Thames-Tokatea rocks, from their northern extremity west of Kennedy Bay, runs south-east across the Haratuunga Valley to the high conical hill noted by Sir James Hector, and described (vide page 10) as seen looking south-west from Kennedy Bay. From this hill to the northern shore of Whangapoua Harbour the boundary has not been determined with exactitude, South of the Waitekauri River, and south of Opitonui Stream, the rocks of this series are at first towards the east limited by the alluvial flats surrounding the inner part of Whangapoua Harbour and extending along the valleys of the streams named. To the south-east of the latter, the Thames-Tokatea rocks extend east from Castle Rock a distance of about four miles, and are then succeeded by a series of rocks of different aspect, and it is on such distinction that the eastern boundary in this part has been determined. More to the south the boundary recedes to the westward, and within the Mahakirau watershed has been determined with tolerable accuracy. South across the Ounuora Valley the boundary of this group of rocks lies within a tract of rugged, hilly, or sub-mountainous country densely clothed with forest, so that within this and thence into the valley of the Waiwawa the boundary is again an approximation. In the Waiwawa Valley younger rocks are met with till passing westward of the northern spur of Table Mountain Range, and it is even not clear but that the east boundary of the Thames-Tokatea rocks should be placed yet further west than shown on the map herewith. From the western source of the south branch of the Waiwawa, the boundary runs along the middle slopes of the northern side of the Kauaeranga Valley to the source of Hape Creek, the south-east side of the valley of which is formed of younger rocks. These rocks within the Thames and Coromandel districts cover an area of 150 square miles, forming the high backbone of the country, but, except from Mata Creek to the Kauaeranga in the southern part, they do not reach on to the coast-line on either side of the Peninsula. Their relation to the slates below, and the other groups of volcanic rocks overlying, may be seen in the section from Kennedy Bay west to the shore of Hauraki Gulf, which shows the arrangement of the different rocks from a little south of the mouth of Tawhetarangi Creek to the low grounds at the head of Kennedy Bay, in which slates and sandstones belonging to the Maitai series are seen at four different parts of the section line. Those in the vicinity of the coast at each end of the section are exposed at the surface along the line, while the other two, more inland, can be seen a little to the north of the line of section. The Cretaceo-tertiary series is also shown in this section. The rocks of the Thames-Tokatea group ; of the Kapanga group; the Beeson's Island group; and the alluvial deposits at the head of Kennedy Bay are also shown.