I. Taupo Volcanic Zone.

The Tarawera Mountain, the scene of the eruption, which is the subject of the present report, lies in the tract of volcanic country which was named by Hochstetter the "Taupo zone." This zone stretches from the south-west of the great volcanic cones, Ruapehu and Tongariro, in a north-easterly direction to the Bay of Plenty. A line passing through Ruapchu and "White Island has a direction 38° east of north, and may be taken as the line of greatest activity at the present time, and as indicating the general direction of the Taupo zone. Upon this line are situated the chief volcanic cones of the district, and fully half of the hot-springs, &c., for which it is celebrated.

It should be noticed further that the line is parallel to the general direction of the mountain-ranges stretching from the neighbourhood of Wellington towards the East Cape. The same line is continued in the South Island in the chain of the Southern Alps. It is worthy of note that in the opposite direction a submarine ridge runs from the East Cape and Bay of Plenty along the bottom of the Pacific Ocean, in a north-north-cast direction, through the Kermadec Islands, and far as the Tonga group. Both these groups of islands are of volcanic origin, and include vents which have been active within recent years.

The islands of New Zealand and the submarine bank to the north north-east may be taken to indicate the position of a band of corrugation of the earth's crust, and the line of activity of the Taupo zone as a line of dislocation or fissure parallel to the axis of this band,

The boundary of the Taupo zone is clearly defined to the east by the high ranges of the Kaimanawa and Whakatane Mountains lying on the right bank of the Rangitaiki River. Both ranges consist of Palæozoic slates and sandstones supposed to be of the Devonio carboniferous age.

To the west the district is bounded by the volcanic table-land which stretches from near Lake Taupo through the Patetere country, and is continued northwards as a mountain-range past Te Aroha and the Thames as far as Cape Colville. This table-land is composed of light-coloured tuffs and volcanic breccias with pumice, considered by Hochstetter to be trachytic. In the Puketapu Hills, to the vest of Lake Taupo, the Palrcozoic slates (Maitai) crop out below the voleanic tuffs, and may be traced at various points to the north.

The table-land gives the direction of a second axis of elevation in the North Island, having at first a northerly direction, though to the north it curves round somewhat to the west as in the Cape Colville page 5 Range and the Great Barrier Island, and the parallel ridge which forms the peninsula north of Auckland. The direction of this axis is continued by a submarine ridge which runs out along the bottom of the Pacific towards Norfolk Island and New Guinea.

It will be noticed that the chief outbursts of the Taupo zone have occurred in the angle between this axis and the north-east axis already Preferred to. In all parts of the world the Tertiary eruptions have frequently appeared at angles of powerful flexures or dislocations of earlier rock-masses,^* as appears to be the case in the present instance.

The western boundary of the Taupo zone is not clearly marked along its whole extent, but almost all the volcanic cones, hot-springs, &c., of the region are confined to a belt of country having the direction of the line joining Ruapehu and White Island, and some twenty-five miles in breadth. (See Index-map, Map I.)

Ruapehu-White Island Line.—In describing the Taupo zone we will take first the various centres arranged along or near the main line stretching from the great cones in the south to the active solfatara of White Island in the Bay of Plenty.

To the south of Lake Taupo we find the lofty volcanic cones of Ruapehu, Ngauruhoe, and the Tongariro group. These lie in a line sixteen miles in length, which differs little in direction from the line joining Ruapehu with White Island. Ruapehu, which lies most to the south, has a cone of great beauty, rising to the height of 8,878ft. above the sea, so that its upper part is covered with perpetual snow. It was supposed to be quite extinct, but has recently shown some slight degree of activity. To the north-east lie Ngauruhoe and Tongariro. Ngauruhoe is the higher (7,481ft.), and has an active crater on its summit. From the floor of the crater steam is constantly rising, whilst ashes, stones, &c., have been repeatedly ejected. In 1869 there was a more severe eruption, and the inhabitants of the district state that lava issued from the crater and flowed down the tone. Mr. Cussen has submitted specimens of the lava of this eruption to me for examination. It is a heavy black scoriaceous lava, of somewhat vitreous lustre; examination with the microscope shows it to be an augite-andesite.

Tongariro is only a few miles to the north of Ngauruhoe; it reaches the height of 5,500ft., and is said to possess several craters, two of which contain small lakes.^† On the northern slope, at the elevation of about 4,000ft., is a hollow named Ketetahi, from which clouds of steam constantly ascend, and there are numerous

^* See King: Survey of 40th Parallel, I., p. 606.

^† See note, infra, p. 21.

page 6 sulphurous springs within the hollow which give rise to a stream of sulphurous water.

To the north of Tongariro, and not far from the southern shores of Lake Taupo, is a group of conical hills known as Pihanga, Kakaramea, and Kuharua. These are probably old volcanic cones; indeed Pihanga has a small crater plainly visible from the north-east, whilst Kakaramea has a group of hot-springs upon it.

How many other volcanic cones exist in the Taupo zone is uncertain. The most conspicuous and best known are Tauhara at the north-east end of Lake Taupo, Tarawera, Mount Edgecombe, and White Island in the Bay of Plenty, all situated on or close to the Ruapehu—White Island line. There are, however, many more or less isolated hills in the district, composed of rhyolitic lava, and a more detailed examination may show some of these to be the remains of extinct cones. Haroharo, for instance, to the south of Rotoiti, is a conical mountain, 2,528ft. high, and the fragmentary rhyolitic rocks on its sides contain numerous obsidian bombs, sometimes of extremely perfect egg-like form, which must have been thrown out from a vent at no great distance, and probably on the mountain itself.

It is not, however, for its active volcanoes that the Taupo zone is famed throughout the world, but rather for its vast numbers of hot-springs, geysers, mud-volcanoes, fumaroles, solfataras, and other manifestations of the minor phases of volcanic activity which are included under the term "hydrothcrmal phenomena." The greater number of these occur on or near the Ruapehu—White Island line, whilst the others may be grouped along two parallel lines to the west of this main line, and will be described further on.

We may suppose that in the Taupo zone masses of heated rock exist at no great depth below the surface. The abundant rain-supply of the district, sinking into the porous ground, penetrates towards the heated masses. The heated water then, following the ordinary laws of, the circulation of underground water, rises along the fissures, or, ill may be, is sometimes forced up by the expansive force due to the high temperature of its vapour. But in most cases it will be noticed that the springs break out at the lower levels, and frequently occur in groups widely distributed over the low country at the feet of til volcanic cones, as, for instance, at Tauhara, at Rotomahana near the foot of Tarawera, and at the Onepu near Mount Edgecombe. In these cases it appears most natural to look upon the reservoirs of heated rock which presumably lie beneath the volcanic cones as the source of the heat of the thermal springs.

Lake Taupo.—Lake Taupo covers an area of nearly 242 square page 7 miles; it is 24 7/8 miles in length by 16½ miles in extreme width. Mr. L. Cussen states that the lake has an almost level bed, the average depth being 390ft.; the greatest depth near the centre is 534ft. In many places the lake is bounded by steep cliffs of rhyolitic lavas and associated tuffs. On the western and northern shores these cliffs range in height from 100ft. to 800ft. Deep water is often found immediately under the cliffs, as, for example, at Karangahape Point. The land rises steeply to the height of 1,100ft. above the lake, whilst at a boat's length from the cliff the sounding of 400ft. was obtained, showing that the rock extends down vertically below the water.

Hochstetter referred the formation of Lake Taupo to the subsidence of its area, and the nature of the cliffs around the lake appears to confirm this view.

The lake had once a wider extent, and a terrace is found above the present shores at the height of 100ft. The Maoris told Hochstetter that the lake used once to stand at the level of the terrace. The fctement, however, does not seem to have been founded on any tradition that their fathers ever saw the lake at the higher level, but merely an inference based on the conspicuous character of the terrace. A second less perfect terrace may be traced at the height of 300ft. or 400ft. above the lake; and at a still higher level the lake is surrounded by the pumice-covered plateau from which the volcanic cones rise. The lowering of the lake is doubtless due to the gradual excavation of the channel of the Waikato River.

Towards the north-east the plateau is continued as a barren expanse, known as the Kaingaroa Plains, covered with pumice, and supporting only a scanty vegetation of lichens, dismal scrub, and tussock-grass, on which troops of wild horses feed. These plains Wretch on the west of the Rangitaiki River, falling gradually towards the Bay of Plenty. They are intersected by terraced watercourses and gullies, sometimes of great depth and with almost vertical sides,

At the south end of Lake Taupo a group of hot-springs and an active geyser are found at Tokaanu, whilst only a short distance away are the hot-springs of Waihi and the group situated on the Kakaramea Mountain.

At the north-east end of Lake Taupo we come to Tauhara, a cone rising to the height of 3,603ft., with sides deeply denuded into gullies, The country at its base to the north and west is remarkable for the hot-springs and other signs of hydrothermal action; but the mountain itself has the appearance of having been long extinct. The River Waikato leaves Lake Taupo at this point, and the hot-springs, &c., we situated on a band of country a few miles in width, occupying page 8 both sides of the river for a distance of six or seven miles. The country immediately at the foot of Tauhara shows signs of vigorous hydrothermal action: the pumice and rhyolitic fragments over a wide area have been rotted into a red or white mud, whilst the surface of the treacherous ground shows small holes due to sinking-in of the decayed rocks, and steam rises in small curling wreaths. There are, however, no springs here, but nearer the Waikato and at a lower level we have the hot creeks and sulphur springs of Loffley's Glen, the Crow's Nest Geyser, one of the most powerful in the Taupo zone, and the other neighbouring springs on the banks of the Waikato, the warm lake and stream at Waipahihi, and the sulphur lake and solfatara of Rotokawa. On the left bank of the river we have the warm creek, Waipuwerawera; the steam-blast of Karapiti, visible for a great distance over the surrounding country; the warm springs at the Huka Falls, on the Waikato; the numerous fine geysers of the Wairakei Valley; and the explosion-crater of the Blue Lake, with its warm springs.

The Waikato River, after leaving Lake Taupo, flows to the northeast in a gorge through the Kaingaroa Plains for some twenty miles, it then turns to the west and cuts through the trachytic range in a deep terraced valley, and leaves the Taupo zone altogether.

The part of the Taupo zone lying to the west of the Kaingaroa Plains has a very rugged character. The older rocks appear to have been dislocated and portions to have dropped down, leaving hollows, some of which were occupied by lakes, whilst rhyolite lavas welled up some of the fissures formed.

If we continue along the main line of activity stretching from Ruapehu to White Island, we find the Ohaki Hot-springs (see map), on the Waikato, near the point where the river turns its course to the west. The line then passes up the Waiotapu Valley to the east of the Paeroa Range, past Kakaramea, and so on to Rotomahana and Tarawera.

The Paeroa Range is a long ridge of mountains parallel to the White Island—Ruapehu line, and rising to the height of 3,244ft,: Hochstetter referred its origin to a dislocation in the district. The western face of the Paeroa Range is very steep; and opposite to it, on the other side of a broad valley, is the remarkable table-topped mountain Horohoro. The summit is quite flat, and the mountain shows to the east a vertical wall-like face of coarsely. Jointed volcanic tuff. The country between this and the steep face a of the Paeroa Range has dropped down, and the steep opposing faces of the two ranges will therefore be the faces of faults. The secondary lines of hot-springs in the district were attributed by Hoch- page 9 stetter to the fissures due to the faults which, extending downwards to the heated rocks below, rendered possible the ascent of heated water. To the north-cast again is situated the part of the Taupo zone which has received the name of the Hot Lakes District. We have here an extraordinary number of lakes within a comparatively small area (see map). These lakes must owe their origin to the volcanic activity of the district, and Hochstetter attributed all the lakes to the subsidence of certain areas. Seeing, however, that many of the lakes—as, for instance, Tarawcra—are surrounded by streams of rhyolitic lava, it appears probable that they owe their formation in some cases to the blocking-up of drainage-channels by the extension of streams or masses of lava.

The Waiotapu Valley and Kakaramea.—The Waiotapu Valley has a nearly north-east direction, and lies between the Paeroa Range and the Kaingaroa Plains; the Waiotapu Stream flowing to the southwest, and discharging into the Waikato. The valley begins between Maungaongaonga and Kakaramea, two mountains composed of volcanic rock, lying a few miles to the south of Rotomahana. Kakaramea is a conical sharply-peaked mountain, rising to 2,494ft., and consists of rhyolitic lava. On its sides, and visible from a great distance, are large tracts of variegated red and white clays produced by the hydro-thermal action to which the mountain has been and still is subject. In the early morning the steam may be seen rising in thick clouds from the mountain, giving the impression of a formidable degree of activity. Several crater-shaped hollows of considerable size exist on its sides, and these appear to have been blown out of the solid rock of which it is built. At the bottom of the craters are hot-springs or pools of warm water. At the base of the mountain and at various points down the valley are irregular basin-shaped hollows, some of them dry at the bottom, others occupied by lakes, the water of which is frequently of a vivid blue or green colour which it is impossible to describe in words. Around the mountain and in the neighbourhood of these hollows the ground is covered with angular fragments of volcanic rock, sinter, &c. These basin-shaped hollows are doubtless explosion-craters, and have been blown out of the ground by the expansive force of steam or heated water which has ascended from below and saturated the rocks until the accumulating tension of the vapour produced a hydrothermal explosion. They are, in fact, similar to some of the craters found at Rotomahana.

Such explosions seem to have been frequent in many parts of the Taupo zone. For instance, the solfatara of Ruahine, near Rotoiti, lies at the bottom of a crater on a hill-side; and the Blue Lake at page 10 Wairakei occupies a hydrothermal crater. It seems probable that many of the smaller lakelets of the district mark the position of basins hollowed by hydrothermal explosion.

About three miles to the south of Kakaramea is a group of hot-springs and sulphur fumaroles. One of the most considerahle of these springs has formed a deposit of sinter, which has received the name of the "Primrose Terrace." On the flat summit of a slight elevation is a platform of sinter some 50yds. in diameter. In the centre is a large circular pool of water, its margin formed by a raised rim of sinter of beautifully-fretted form. The water appears to be in a state of ebullition; it showed however at the time of my visit a temperature of only 170° Fahr., the apparent ebullition being due to the escape of gas. The water flows down a gentle slope, which spreads out in a fan-like shape. This slope is covered with greyish-white sinter, which is not properly terraced, but shows very beautiful ripple marks. To the right is a pool of intensely yellow (or sometimea orange-red) mud, which owes its colour to the presence of sulpha containing selenium. This is, I believe, the first time that this scarce element has been described from the district. It has been found associated with sulphur in other volcanic regions; as, for instance, in the Lipari Isles, which like the present district is characterized by rhyolitic rocks.

The water from the terrace forms a stream which flows over a waterfall into a gully, and then with winding course passes into a chain of crater-like excavations. The bed of the stream and the rocks at the waterfall are covered with greyish-white sinter, with here and there patches of a purer white. The course of the stream is also marked by other small hot-springs; and just below the waterfall is joined by a small stream from the left.

Carried along on the surface of the latter stream are vast numbers of small black beads of an oval or pear-like form and shining lustre. These were about ¼in. in diameter, and an application to the flame of a candle showed they contained much sulphur, Analysis proves that they consist mainly of sulphur, discoloured by black mud. I had not an opportunity of following up the stream, and tracing these curious objects to their origin; but Mr. Percy Smith informs me that they appear to be brought to the surface by water welling up from the centre of a small lake. The lake appears to be of considerable depth, and as the beads are evidently formed front melted sulphur it is probable that a hot-spring containing sulphur exists at the bottom of the lake at a sufficiently high temperature to melt sulphur, and that the beads of sulphur are thrown up by the page 11 escape of gases. Sulphur melts at 114.5° C., but does not generally solidify till 111° C., and at the depth of 20ft. below the surface water would not boil at 100° but at about 111° C.

To the south of the terrace mentioned are numerous other groups of hot-springs, and to the north, on the slope of Maungaongaonga, a very active group is situated. There are sinter deposits forming small terraces, but none which at all approach in beauty to the Rotomahana Terraces destroyed during the recent eruptions. The whole region of the Waiotapu Valley, however, is one of very great interest, and is likely to become well known to visitors.

The next points of activity along the Ruapehu—White Island line are Rotomahana and Tarawera, but the account of these is placed later so as to precede the description of the eruption.

Mount Edgecombe.—Passing further along the line we come to Mount Edgecombe, a volcanic cone of typical form, about fifteen miles north-cast of Tarawera Mountain. It rises boldly above the low hills where the Kaingaroa Plains pass down into the Te Teko Swamp. Near Te Teko the ground is but little above the sea-level, and the area between this point and the seashore between Matata and Whakatane is practically a delta formed by the Whakatane, Rangitaiki, and Tarawera Rivers, so that much of it lies low and is swampy. As seen from this low ground near the Bay of Plenty, Mount Edgecombe presents a conspicuous land-mark, standing prominently up above the surrounding low country. The sides of the cone from almost every point of view present an unbroken curving slope of 27° to 33°. As the volcano had never, so far as I was aware, been visited by any geologist, I took the opportunity of a visit to the agricultural districts to ascend the mountain. Its sides are thickly covered with vegetation, especially on the western side, where the bush is extremely difficult to penetrate. The top of the mountain is obliquely truncated; the highest point being to the east, and reaching the height of 2,946ft. On the top of the mountain are two craters; the first is of regular circular form, about 300yds. in diameter, with sides of varying height I covered with large forest trees and sloping down to a trefoil-shaped lake of green water. This lake was about 120yds. in greatest diameter, and its waters had a very strong mineral taste, like that of many hot-springs. The water, however, was cold, and it seems probable that the mineral matter was not derived from springs in the lake but had been dissolved out of the ashes from the late eruption of Tarawera, which covered the sides and bottom of the crater.

The second crater is of less regular form; it has high steep sides, and to the south-east its side is broken down, and the cavity of the page 12 crater is continued down the side of the mountain as a gully excavated by the rain-water which falls within the crater and flows outwards by the gap.

Huge masses of lava crop out on various parts of the mountain, hut the greater part of the surface is thickly covered with luxuriant vegetation, partly of forest-trees, partly of tutu and bracken-fern, the latter growing to the height of 8ft. or 12ft. The thick covering of Tarawera ashes, too, did much to conceal the character of the superficial rocks.

On the inner slope of the first crater the ashes were 14in. in depth. We have here the curious phenomenon of a volcanic mountain thickly covered with the scoria; from another, fifteen miles distant. If an eruption of Mount Edgecombe were to occur before the scoriæ had time to decay or be removed by denudation the layer might be preserved, and if ever brought to light again at some future period would scarcely be referred to so distant a source as Tarawera. This example shows that the scoria; found on any volcano are not necessarily derived from an eruption of that volcano but may possibly have their origin from a distant vent.

The thickness of the vegetation, the amount of ash, and a rainy day precluded a detailed examination of the mountain in the time available. All the rocks seen by me, however, were augitc-andesitea, and I saw none of the rhyolites supposed to be so characteristic of the Taupo zone. The commonest variety was a dark-grey rock showing numerous felspar crystals, reaching the size of a pea, and smaller augites.

The Tarawera River, which drains the lake of the same name, flows past the western foot of Mount Edgecombe, and on the bank of the river opposite the mountain are the hot-springs and sulphur-deposits of Oncpu. There are numerous hot-springs here, and deposits of sulphur so abundant that they are worked and the sulphur sent to Auckland for the manufacture of sulphuric acid. The crude sulphur as it comes to market contains 80 per cent, of pure sulphur.

The thick vegetation on the mountain, and the size of the rimu and other forest-trees, show that it is long since Mount Edgecombe has been in activity—certainly not since the Maoris have been in New Zealand. The hot-springs of the Onepu would seem, however, to be connected with the heated rocks below the mountain.

A few miles from Te Teko a large hot-spring rises at the foot of the low ridge of hills along the base of which the road to Whakatane winds. There is a copious supply of water at a temperature of about 140° Fahr.

A few miles from the coast between Matata and Whakatane are Whale Island and the Rurima rocks, composed of volcanic rock. Hot-springs are found on Whale Island, and Major Mair^* states that on the neighbouring Rurima rocks the ground may be seen steaming in places when the condition of the air is favourable, and that at one time the islands must have abounded in hot-springs.

The last point along the main line of activity in the Taupo zone is formed by White Island, a volcano which is now in the solfatara stage. In the centre of the island is a crater, half a mile in diameter, which until recently was occupied by a lake of acid water. From the I crater a dense cloud of steam constantly rises, and forms a white cloud I visible for fifty miles around.

Most of the other hot-springs in the Taupo zone may be grouped along two lines parallel to the main line from Ruapehu to White I Island. It appears probable that these lines of springs are due to fissures extending through the surface rocks to the region of heated rock; the surface waters which sink down over the whole of the neighbouring country coming in contact with the heated rock and rising at those points where the line of fissure allows them an easy I. ascent.

1. The first of these lines is situated to the cast of the main line, the distance between them being about seven miles. At the south end of this line are the numerous hot-springs, fine geysers, and sinter terraces of Orakei-korako, on the banks of the Waikato. Then to the north-cast are the hot-springs and fumaroles on the eastern face of the Paeroa Range. At the north end of the line, thirty-seven miles I; from Orakei-korako, are the hot-springs of Rotoehu. Hochstettcr was of the opinion that the low-lying country between the Paeroa Range and Horohoro to the west had been thrown down, and that the first line of hot-springs corresponded to the line of fault at the foot of the Paeroa Range, whilst the next line of springs would correspond with the line of fault to which the steep face of Horohoro owed its: origin. It will, however, be noticed (see Map I.) that the face of Horohoro is not quite parallel to the direction of the line of hot-Springs.

2. The second line of hot-springs is still farther to the west, being about eight miles from the first line. Near the south end of the line are the hot-springs near the Waipapa Creek, a tributary of the Waikato. On the banks of the Waikato at Niho-o-te-kiore are some small hot-springs, and the rocks on the river-bank in the neigh-

^* Trans. N.Z. Inst., Vol. V., p. 151.

page 14 bourhood show brilliant red fumarole clays. A mile or more to the north-east are the hot-springs and sinter deposits of Waipupuwerawera. The Maoris inform me that a small hot-spring exists to the south of Haperangi (east of the Taupo Road), and blocks of sinter lie along the roadside near here; but the next considerable group of springs is at Whakarewarewa, at the south end of the Rotorua basin. Here at the foot of a ridge of rhyolite rocks are numerous fine geysers with extensive sinter deposits.

All along the southern shore of Rotorua are the innumerable hot-springs of the Rotorua Township, Ohinemutu, and Te Koutu, I Further along the line we meet with hot-springs on Mokoia, the island of rliyolitic rock in the centre of Rotorua, the solfataras of Tikitere, Ruahine, and the hot-spring at Manupirua, on the shore of Lake Rotoiti. Some small hot-springs occur also near the coast at Maketu, but it is doubtful whether these should be referred to the Rotorua line.

It may be well to mention here that, if these two lines are produced to the south-west, they will be found to coincide with the general lie of the western shores of Lake Taupo. The Rotorua line corresponds with the west shore of the lake in that portion of the lake known as Western Bay, whilst the Orakei-korako line coincides with the western shores of the lake south of Western Bay. This circumstance suggests that the fissures marked by the rise of hot-springs are the continuations of those dislocations which have determined the position of the shores of Lake Taupo.

Rocks of the Tavpo Zone.—The most complete account of the rocks of the Taupo zone has been given by Hochstetter. He states^* that all the rocks collected by himself around Lake Taupo and throughout the district, as far as the Bay of Plenty, belonged to the family of rhyolites. He mentions elsewhere, however, the trachytic tuffs as forming the western boundary of the district. So far as I am aware, no other rocks were described from the district before the time of the eruption of Tarawera, but to these must now be added the augite andesites, occurring not only amongst the recent ejecta from Tarawera, but also at Ruapehu and Ngauruhoe in the south, and at Mount Edgecombe to the north of the zone.

1. Older Volcanic. Tuffs.—The older tuffs of the volcanic tableland forming the western boundary of the Taupo zone were described by Hochstetter as trachytic, and are probably of submarine origin. As found between Oxford and Rotorua the tuff is a soft lilac-coloured rock containing numerous broken crystals of felspar, of which a fair proportion are triclinic, and quartz-crystals in double hexagonal pyramids^* This rock forms the whole of the hills to the west of the Rotorua basin, north of the mountain Ngongotaha. The hills to the north of Rotorua are composed of the same tuff, and the streams have excavated very deep ravines in it, as, for instance, the picturesque Mongarewa Gorge, through which the Tauranga Road passes. It is found farther along the same road as far as Oropi. To the cast of Rotorua it crops out in a few places amongst the hills, as, for instance, to the east of the Ngae.

Farther to the south the tuffs are light-coloured rocks with considerable quantities of pumice. In the opposite direction, north of the Cambridge Bush and near Matamata, there is a break in the character of the rocks forming the range. The lilac-coloured tuff gives way to massive augite-andesite rocks and the altered forms of volcanic rocks known as propylites. It is in these altered rocks that the auriferous reefs of the Thames and Te Aroha Goldfields occur.

2. Rhyolidc Lavas and Tuffs.—The predominating rocks of the Taupo zone are rhyolites. The rhyolites form a group of volcanic rocks characterized by the high proportion of silica they contain—70 to 80 per cent.,—and frequently the excess of silica in the rock has separated in the form of crystals or glassy blebs of quartz. The rhyolites are remarkable for the great number of varieties in which they occur. Zirkel has given the most complete description of the rliyolitic rocks.^† He divides them, according to their structure, into the following groups:—

(1.)	Nevadites or granitic rhyolites—varieties which appear to the naked eye to have a completely crystalline character. A more careful examination however always shows a certain proportion of ground-mass in which the crystals are imbedded.
(2.)	Rhyolites proper—the liparites of Von Richtliofen. These include the felsitic and porphyritic varieties. The former have a dull * The abundance of quartz-crystals in some of the tuffs suggests that the rocks are really rhyolitic. Sections of the tuffs, owing to the more or less altered character of the block, do not afford very conclusive evidence. They contain, however, fragments of rock with a felsitic base, which point rather to the rhyolites. The writer has thought it desirable to make a more extensive examination before altering Hochstetter's term. † "Microscopical Petrography," p. 8. page 16 stony-looking or felsitic ground-mass, which may or may not include crystals recognisable by the naked eye: the latter consist of numerous crystals of quartz, felspar (chiefly sanidine), and sometimes black mica, hornblende, &c., imbedded in a distinct ground-mass which is of very variable character in different varieties.
(3.)	The glassy or hyaline rhyolites, which consist entirely, or in very large part, of glass. Many obsidians, pitchstones, pumice, and perlites belong here.

I have not met with any of the nevadites in the Taupo district. Zirkel,^* who examined the rocks collected by Hochstetter, states that a nevadite occurs at Mokoia, the island in the centre of Lake Rotorua. The only rocks, however, which I collected on the island belong to the rhyolites proper. The rhyolites proper and the glassy rhyolites are represented by very numerous and interesting varieties.

Massive rhyolites or rhyolitic lavas occur in very many places around Lake Taupo, sometimes forming steep cliffs or bluffs rising above the waters of the lake. To the north of the lake the rocks showing, which crop out from beneath the superficial deposits of pumice, are chiefly light-coloured tuffs with pumice, until we approach the Hot-lake district. There is, however, a large patch of rhyolites (spherulitic obsidian .and felsitic varieties) about six miles south of Atiamuri. The picturesque Atiamuri rock, which rises with vertical sides high above the valley of the Waikato, is composed of a laminated rhyolite. Rhyolitic lavas are also found to the west of Atiamuri and in Maungaiti. On the south-east border of the Rotorua basin the mountain Ngongotaha (2,554ft.) is composed of a spherulitic obsidian. The southern boundary of the basin is formed by a ridge of spherulitic obsidian, which stretches from the west of the Hemo Gorge to the old Mairangi Pa, overlooking the Wairoa Road. Most of the hills between Rotorua and Lake Tarawera are composed of rhyolitic lavas. The following are the commonest types: (a.) A spherulitic obsidian, composed of a black volcanic glass, in which are imbedded large numbers of round bodies about the size of small peas (1/8in. to ¼in. in diameter). These are sometimes bluish-grey in colour; more frequently they are pink or red, or when weathered they may be of a rich orange-brown, (b.) A porphyritic variety of a light-greyish colour. Crystals of felspar, quartz, and black mica are imbedded in a light-coloured porous ground-mass, which the microscope shows to be a porous glass. (c.) Porphyritic obsidian, a black volcanic glass, with a small number of crystals of quartz and felspar.

Pumice.—The surface of the ground over the greater part of the Taupo zone is composed of pumice, or of a soil formed from the decay of pumiceous material. These deposits extend far beyond the belt of country which forms the Taupo zone, being found nearly as far as Napier to the south, and Lichfield to the north.

Moreover, immense quantities of pumice have been and still are being carried down by the rivers which radiate from the centre of the North Island—as, for instance, the Waikato and Ongaruhe. The courses of these rivers are marked by valleys, which have been filled up with immense quantities of pumice sand and gravels, out of which the river has excavated the numerous terraces for which the valleys are so remarkable. As will be seen below, much of the superficial pumice in this district has been distributed in the form of great showers of ash, resembling in character, and probably exceeding in magnitude, the shower which fell during the recent eruption of Tarawera. Around Lake Taupo the country is covered to a great depth with pumice; and the cliffs around the north-east shores of the lake, rising to the height of 300ft., consist entirely of stratified pumice.

This pumice extends to the north-east, covering the Kaingaroa Plains. Towards Lake Taupo the tributaries on the right bank of the Waikato have cut deeply into these loosely-compacted strata, and now flow in ravines with vertical sides, rising to 100ft. or 200ft. or more. These gullies represent miniature canons, and the preservation of their vertical sides is due largely to the porous nature of the strata, which allows the rain to sink into the ground, instead of streaming over the surface and wearing water-channels along the margin of the canon. The preservation of the steep faces of the canons of the Western States of America is attributed to the almost rainless character of the region. Here, where the rainfall is considerable, the same effect is produced by the porous nature of the strata. Huge blocks of pumice are found along the shores of Lake Taupo; and the Kaingaroa Plains for the distance of twenty miles towards the sea are covered with blocks of considerable size, becoming smaller as the distance from Taupo increases.

These vast accumulations of pumice have been attributed to the great volcanoes of Tongariro and Ruapehu; but I have found that the pumice becomes distinctly less abundant towards the south end of Taupo, and that on the lower slopes of Tongariro it is seldom 3ft. thick, and is often much less. Beneath the pumice the mountain is composed of basic lavas or ashes. It may, perhaps, be suggested that much pumice may have been buried under the lava and ashes of more page 18 recent eruptions of Tongariro; but, as pumice now lies on the surface, it is clear that eruptions of pumice have taken place at some point in the Taupo district since the last great eruption of Tongariro. Moreover, fragments of rhyolitic rocks are scarce amongst the ejecta on the top of the mountain.

The pumice has also been attributed to vents occupying some portion of the area of subsidence covered by Lake Taupo. As evidence bearing upon this point I may mention that the pumice around the lake contains considerable quantities of the laminated rhyolite which has been called lithoidite. I have found blocks of it embedded in the pumice which reached the diameter of 4ft. Such blocks must point to an origin at no very great distance. The only locality near Taupo known to me where this peculiar variety of lava is found in situ (and not in loose fragments) is Motutaiko, the island in the lake. The significance of these facts need scarcely be pointed out.

Records of former Showers of Ashes.—Although the Taupo district abounds at the present time in the minor manifestations of volcanic energy, it does not seem to have been the scene of any considerable eruption for many centuries past. If any eruption of the magnitude of the recent one had occurred since the arrival of the Maoris in New Zealand, some five or six centuries ago, they would, we can hardly doubt, have preserved the tradition of it. But there is nothing in their traditions which hints at any such great volcanic catastrophe.

Trusting, however, to the present being the key to the past history of the earth, we may well believe that eruptions of the kind and degree of that of 1886 have occurred again and again in the district, and we may therefore ask whether there is now any trace of showers of ashes having in past time overwhelmed large areas of the North Island. A careful study of the mode of distribution and arrangement of the ashes which fell recently, will form a safe foundation for the interpretation of the traces of former showers which may be left on the surface of the country, or included in old lake-deposits which are now again laid bare by denudation.

The principal characters by which we may expect to identify an old shower of ashes are the following:—

(1.)	The deposit will follow the contour of the former surface upon which it fell.
(2.)	The ashes will show a more or less pronounced stratification which will follow the old surface of the land.
(3.)	The coarser fragments will, generally speaking, be the lowest, then will follow the finer, and lastly the finest dust.page 19
(4.)	The fragments for the most part will be angular or rough. They will consist mainly, if not entirely, of fragments of volcanic rocks, especially the porous ones (pumice and scoriæ).
(5.)	As we approach the source of the ashes the deposit will be thicker, and the component fragments larger. Close to the source, however, there will be less regularity in the arrangement of the ashes.

We may expect to find the deposit wanting in many places, as, for instance, where it has been exposed to running water, or on steep slopes whence it may have been washed by the rain. In other places the conformation of the ground may have allowed a greater accumulation, as at the foot of slopes. The deposit will have been subject to decomposition, and wherever it was thin it may have been obliterated by the progress of decay into soil.

Applying such principles to the study of the superficial deposits in the district, we may note the existence of the remains of several distinct showers of ashes, each of which has fallen over a wide area of country.

Rotorua Shower of Ash.——We will consider first a shower of pumiceous ashes which, for the sake of distinction, may be called the Rotorua shower, as it is well marked in the neighbourhood. All around the basin in which Lake Rotorua lies the present surface is formed by a pumice-ash some feet thick, in layers which follow the contour of the ground, the coarsest fragments being below, the finer at the top passing into a brown pumiceous soil. The greatest thickness of the ashes, so far as I observed, was along the Wairoa Road, about three miles east of the Rotorua Township. There the ashes varied from 7ft. to 10ft. (in one place 15ft.) in thickness. The surface-layer, of course, consisted of soil, a brownish pumiceous loam stained with vegetable matter: this passed down into a brownish sandy substance, which doubtless represents the finer pumice-ash, for small pumice-fragments were to be detected in it. This gradually becomes coarser and less decomposed in character till at 4ft. from the surface it passes into unmistakable but fine pumice-ash. Below, the pumice-fragments grow larger, and are arranged in distinct strata with a peculiar wavy character about the layers, which reproduces the details of the stratification shown by the ashes of the late eruption of Tarawera. The coarsest fragments are at the bottom, and reach i the diameter of one or two inches, or exceptionally as much as 4in. Below the pumice is a brown loamy layer, which, doubtless, represents the land-surface which was overwhelmed by the ashes above. About 85 to 90 per cent. of the fragments consist of a pumice weathered buff or cream-coloured outside, but white and fresh within. page 20 The remainder consist of fragments of obsidian, pitchstone, and various rhyolites. All the largest fragments are pumice.

The layers of this pumice-ash follow the present contour of the land, and this character, as well as the freshness of much of the pumice, seems to indicate that the shower took place at no very distant date—probably not long before the Maoris came to New Zealand. On the west side of Lake Rotorua are to be seen old lake-beds deposited when the water stood at a higher level, before the drainage-channel to the north was lowered. The lake had been lowered and the lake-beds subject to denudation before the pumice-shower fell, as may be clearly seen in the sections afforded by the road-cuttings.

I have traced the present deposit in various directions, and its characters conform everywhere to the principles formulated above. It will not be necessary to enter into details, but simply to state that to the west it may be traced for twenty-four miles along the Rotorua-Oxford Road. The soil in the forest along this road (Cambridge Bush) is brown; below it passes into a yellowish more or less fine pumice-ash. The last distinct trace of this is seen at a point ten miles east of Oxford; but the character of the soil would seem to indicate that the shower extended farther to the west, though now all the fine ash is decomposed. To the north it may be traced along the Tauranga Road past Awahou as far as Oropi, thirty-two miles from Ohinemutu. Along the Maketu Road it may be followed as far as Waiwhakaretu (twenty-nine miles). To the south the ash may be seen at Pakaraka (eleven miles from Rotorua), where it is still several feet thick, and at Pareheru. It may also be traced still farther along the Wairoa Road to Tikitapu and Rotokakahi; but the thickness of the more recent ash renders continuous observation difficult here, and I have had no opportunity of detailed study.

The interesting question of the source of this vast shower of pumice, which spread over so large an area of country, must therefore be left for the present undecided; but the direction in which the ash thickens points to an origin either near Tikitapu or Rotokakahi, or in the same direction.

The remains of other pumice-showers may be distinguished farther to the south of the Taupo zone. The road-cuttings on the Taupo-Rotorua Road south of Atiamuri show sections with two, or perhaps three, layers of volcanic ashes, as follow:—

(1.)	Soil.
(2.)	Pumice in angular fragments, 1ft.—3ft.
(3.)	Fine bluish-grey ash, ½in.page 21
(4.)	Brown sandy layer (old soil), 1ft.-2ft.
(5.)	Pumiceous ash.

Pumice belonging to Layer No. (2) above shows on the tops of all the hills between Atiamuri and Orakei-korako, and Professors Brown and Hutton inform me that they traced this deposit to the west as far as Lichfield. It was traced by myself northwards past Horohoro, where it was 6in. to 12in. thick nearly as far as the Hemo Gorge, within three miles of Rotorua. This shower must therefore have affected a very wide area of country, and the direction in which it thickens indicates an origin in the Taupo neighbourhood. The bluish-grey ash was very irregular in its distribution, being often wanting, or washed down into the underlying layer. It could, however, he distinctly recognised as far north as within seven miles of: Rotorua. Its thickness increases as it is traced southwards: eight miles to the south of Atiamuri it reaches the thickness of one inch. This ash is curiously similar in colour to the ash of the recent Tarawera eruption, but differs in its microscopic characters. This layer must have been covered up by the pumice-ash soon after it fell.

Immediately underlying the grey ash is a sandy layer of coarse brown colour. This doubtless represents an old soil; indeed, the upper part is sometimes coloured a darker brown, as if it still contained humus or colouring-matter of vegetable origin. Below the old soil was another layer of white pumiceous material, which probably represents another pumice-shower.

3. Augite-andesites.——As mentioned above, the recent lavas of Ngauruhoe are composed of basic lava——that is, a lava possessing a lower proportion of silica and a higher proportion of the metallic bases (alumina, iron oxides, lime, magnesia, soda, &c.). I have described these rocks elsewhere, and shown them to be augite-andesites. Similar lavas occur on Ruapehu; and Mr. Cussen informs me that around Ruapehu and Tongariro there is much less pumice^* than elsewhere in the Taupo district, the soil being of a darker-brown colour and greater fertility. It seems probable that this soil has resulted from the decomposition of ashes from the eruptions of the more basic lavas which seem to have succeeded the rhyolites.

Augite-andesites occur also at Mount Edgecombe. The commonest variety is a rock with a dark-grey ground-mass, in which are imbedded numerous felspars, which may reach the size of a pea, and smaller dark augites. The sections for the microscope show that the felspars are chiefly plagioclase, though sanidines are present. The felspars are sometimes remarkably full of inclusions of brownish glass; sometimes they are so numerous that only a narrow rim of the felspar substance is left free from them, forming a kind of frame to the rest of the crystal. The ground-mass consists of microliths cemented by grey glass and with a few magnetite grains. In another variety a similar ground-mass shows patches of brownish glass free from microliths like that which forms the felspar inclusions.

Augite-andesite also forms the lava from the recent eruption of Tarawera, as will be shown further on.