Surface and ITydrography. -- The mountain system is not yet thoroughly known. The northern headland and the long and narrow isthmus have been already noticed. Where the island widens, it is flat, with a few hills, till we reach 35° 5' S. lat., where commences a ridge of elevated hills, lying nearly north and south, in which are the upper sources of the Wairoa River, the basin of which lies between it and a parallel ridge along the western coast. Another small ridge lies in the same direction north of Auckland, throwing off numerous streams on their western elope into the harbour of Kaipara. The country extending along the western coast south of Manukao, as far as the river Mokau, appears to rise to a higher level than the northern districts of the island. The shores have in many places a low sandy beach ; in others they are lined by sandhills, but there are also large tracts where the sea washes the base of steep cliffs composed of sand stone and conglomerate. A few miles from the sea the country rises higher, and contains numerous hills, whose declivities are gradual. Some miles north of Waitemata Harbour the hills sink down, and the narrowest part of the island, which is between this harbour and Manukao Harbour au the western coast, has a slightly undulating surface, on which several isolated bills rise to some height. Where the Gulf of Hanraki grows narrow, opposite the island of Waiheke, the country rises to a higher level, and presents towards the gulf a hilly ridge, in which several narrow valleys open to the (estuary of the Waiho. This billy ridge continues southward, where it separates the valley of the Thames or Waiho and of the Piako from the basin of the Waikato River ; but it sinks lower as it proceeds towards the source of the Thames, or rather the general level of the country rises higher. This chain of hills is mostly composed of basalt, and wood is only found in some small valleys and ravines. The valley of the river Thames, which lies to the east of this hilly range, and begins at the most southern branch of the Gulf of Hauraki, is the largest known plain in New Zealand. It extends about 60 miles south, terminating in the low hills of Horohoro, where the river Thames originates. At its northern extremity it is about 20 miles wide, but grows narrower as it runs southward, though probably in no part does it fall short of 10 miles in width. The plain of the Thames is separated from the Bay of Plenty by a ridge of rocky hills, which begins at Cape Colville, at the entrance of the Gulf of Haraki, and continues without inter ruption for more than 100 miles to the Horoboro Hills at the source of the Waiho. They are called the Ahora (Love) Mountains, and rise about 1500 feet above the sea. North of the mouth of the Thames they fill up the whole extent of the peninsula terminating with Cape Colville, but farther south they are a few miles distant from the banks of the river. Their western declivity is very steep, and rises like a wall over the plain of the Thames, but towards the Bay of Plenty they descend with a gradual elope. They are almost entirely covered with wood. North of 33° S. lat., the highest portion of this tract does not appear to rise more than 1500 or 2000 feet above the sea-level, and the bills do not run in any determinate direction.
South of the parallel just mentioned they take the shape of a con tinuous ridge, running parallel to the western coast, and rise much higher. This chain is called, in its northern portion, Rangitoto; in the centre, Rua Wahine ; and towards its southern extremity, Tara rua, which last terminatesait Cook Strait. Mount Taranaki or Egmont occupies the centre of a projecting headland, and is about 20 miles from the shore, in 39° 3' S. let., 174° 1' E. long. It is an extinct
volcano, which rises 8839 feet above the sea-level, and is above the snow-line. It is a perfect cone, from the base of which the country slopes slowly towards the sea on tho north, west, and south; and on the east it is surrounded by a hilly region, which extends to the Rangitoto Chain and the volcano of Tongariro. Taranki is the western extremity of a volcanic region, which traverses the island from south west to north-east, and terminates on the southern shores of the Bay of Plenty. The Rangitoto Mountains contain the active volcano of Tongariro and the extinct volcano of Ruapahu. North of the firat named peak is the Lake of Taupo, which is surrounded by bills of volcanic formation, from the rents of which numerous hot-springs rise, and which are interspersed with mud volcanoes. Towards the shores of the Bay of Plenty is a large cluster of lakes, some of them filled with hot-water, and others surrounded by hot-springs and volcanic rocks, the most remarkable of the lakes being that of Rotorua. The Rangitoto range extends from 38°, after throwing off the branch to Taranaki south by east, to the peak of Tongariro, and then south to that of Ruspahu. about 70 miles. Their general elevation probably does not exceed 2000 feet above the sea, at least not north of Touga riro. This summit rises to 6200 feet, and that of Ruapahu reaches far above the snow-line, and is supposed to be at least 9000 feet high. Between these two summits and in their neighbourhood the range appears to attain its greatest elevation. But these mountains occupy a comparatively small width, hardly more thau 4 or 5 miles. On the west of them extends a hilly region, whose general level is probably less than 1000 feet above the sea, but the hills upon it rise about 500 feet higher. On the east of the Rangitoto Range is the basin of the Waikato River. Beyond the valley of the Waikato to the east, in the tract forming the great promontory ending at East Cape, the country is broken and mountainous, but with few remarkable heights, though there are several which rise to a considerable height at its northern extremity, and Mount Edgecombe to the east of Rotuma. The two mountain ridges which inclose Port Nicholson and the valley of the Eritouga unite at the source of the river, and are there called the Tararua Range. This chain, consisting of several ridges, runs south and north, and extends to the elevated peak of Ruapahu, where the Rangitoto Mountains begin, which are to be considered as their northern continuation. The geological structure of the Tararua Mountains is argillaceous schist, interrupted, especially on the western side, by bulky and irregular dykes of red, black, and greenish Lydian stone. Sometimes the clay is more quartzose and granular, and forms a good stone for building purposes. These mountains apparently do not rise more than 3000 feet above the sea-level. They extend in longitudinal ridges, with narrow crests here and there rising to a somewhat higher summit. In many places they are overgrown with forest, in others the woody region does not quite reach to the top. In the country extending from the Tararua Mountains to Cook Strait the southern portion, as far as Paripari, is filled up with the offsets of the mountains. At the last-mentioned place the chain begins to recede from the sea-shore, increasing its distance from the coast-line as it runs north. The mountains are now succeeded by a belt of low sandy hills, commencing at high-water mark and widening as the mountains fall back, till, at the Manawatu River, the sandy belt is 9 miles broad. From the south-eastern extremity of the island a range of mountains extends to near Cape Matsu, known as the Mamigaraki and Pakatoi Mountains.