I-'.MUH HAHi^ON. — TJw I'Jdtiiium Graveh of Orcjniki. 459 



Look now at the Coromandel district. It also consists mainly of a 

 mountain-ridge running nearly north and south, with numerous spurs, and 

 all densely wooded. Tlie base or bottom of the structure consists of Palaeo- 

 zoic slates, which are also pierced by dykes. The latter are composed of 

 trachyte, and what was originally called by Captain Hutton a diorite, and 

 what has since proved to be in some cases a dolerite and in others a mela- 

 phyre. Further, the older formation forms the centre, and younger form- 

 ations of Tertiary age form the outskirts. Brown coal also occurs in the 

 peninsula in places, I'esting unconformably, as in the Longwood, on the 

 older slates. 



In addition, it may be remarked that quartz veins occur in the Coro- 

 mandel, and they also occur on the south-eastern slopes of the Longwood. 

 Gold, too, is found in both localities. 



A similarity is also to be noticed with the structure of Great Barrier 

 Island, north of Cape Colville Peninsula. This, as Captain Hutton points 

 out (New Zealand Geology Reports, 1868), consists of a base of dark-blue 

 siliceous slates, penetrated here and there by dykes of quartz-porphyry 

 and what he calls a diorite, but which may be of similar character to the 

 diorite of the Coromandel dykes — i.e., either dolerite or melaphyre. 



There is, however, a marked difference in the associated volcanic rocks 

 in the two districts. In the Longwood district the only volcanic rock is 

 the basalt already described, but in the Coromandel district hypersthene- 

 andesites were first erupted, and these were followed by large outpourings 

 of rhyolites characterized by the presence of tridymite. The andesites 

 are everywhere older than the rhyolites. 



Round Hill District and Claim. 



General Appearance. 



It will be seen that the country to the north consists of Round Hill 

 and two chief ridges. Round Hill has a barometric height of 1,120ft., 

 and the ridges of approximately 703 ft. and 8J0 ft. respectively. Between 

 the Hill and the first ridge there is a gully, down waich the Rurikaka 

 Stream flows. Between the first ridge and the second occurs a steep- 

 sided gully, down which flows in a rapid stream the main branch of the 

 Ourawera River. Between the second and the third ridge occurs anot ler 

 similar gully, down which the other branch flows. A rather similar 

 succession goes on all round the lower spurs of the Longwood R mge. 



In a southerly direction from the Rurikaka a rather peculiar knob is 

 found, bordered on the far side from Round Hill by the Ouki Stream, the 

 bed of which is flatter than that of the other streams above it. From this 

 stream, both on the east and on the west side of the district, a more or less 

 gradually rising slope occurs, extending on the west towards Pahia and on 

 the east towards Riverton. 



It Will thus be seen that the Ourawera River flows in a kind of obtuse 

 V-shaped hollow, rising rather abruptly to the north, and sloping gradually 

 from tiie base of the ridges to the sea. On each side the land rises fairly 

 riipidly, but more so on the east than on the west, and the slope increases 

 as we go towtirds either the north-west or north-east. Thus the greatest 

 height of the land on the west side (with the exception of the knob pre- 

 viously mentioned) is about 500 ft., while on the east side it may rise to 

 700 ft." 



