The report of the Colonist newspaper, to which I am indebted for most of the above details, concludes that the shock was more severe than that of the 19th October, 1868: this is almost certainly correct—indeed, it is the most considerable earthquake felt in New Zealand since the 23rd January, 1855.

The effects noted at Wellington were well marked in character, but far less in degree of intensity than at Nelson. The most important from the point of view of the present investigation were the stopping of clocks, the ringing of bells, the cracking, and in some instances the fall, of plaster, the overthrow of movable objects, the cracking of some walls, and the fall of a few chimneys, probably already out of repair.

In the Post Office buildings pendulum-clocks at right angles to the line of shock (E. and W.) were stopped, and all the western walls where the plaster of the ceiling joins the wall were cracked, and chips of plaster deposited on the dado moulding. It is interesting to remark that the seismometer at the Museum showed a large displacement, and registered movements both from east to west and from north to south—that is, it showed both the longitudinal and transverse vibrations.

As will be seen from what follows, the velocity of propagation was much greater than the average velocity of New Zealand earthquakes; and this, coupled with the undoubted fact that the shock was a compound one, made the determination of the origin more than usually difficult. A small error in time is of far more importance with a large than with a small velocity; and when two shocks follow closely on one another, and one of them only is felt at many of the places, it becomes a matter of some difficulty to determine which shock it was that was observed at any particular place. There is, in addition, the usual amount of uncertainty as to whether the same phase of a long earthquake is referred to by different observers—all being asked to give the time of the beginning of the shock. The time put down for the apparent duration is of some service in resolving this uncertainly. Using this and the other means of checking the times given, I have set down the times at the first five places in the list (a) as of greater weight than the others. The times in this list and in the second list are stated to have been all checked by New Zealand Mean Time by the Telegraph officers, who filled up the forms supplied to them. The times in the third list (c) were not so verified.

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propagation assumed is 50 miles per minute, and this solution agrees also with Wanganui (8·4), and Westport (8·3) nearly, and is only ¼min. out for Picton (8·2).

(y) The method of co-ordinates: The times in the list (a)—all verified by New Zealand Mean Time, and apparently good times, referring to the same phase of the same shock—were employed. Christchurch was taken as the origin of co-ordinates, the line Christchurch-Hokitika as the axis of y, and the axis of x at right angles (north-easterly).

The reduced equations are—

• Opunake), 544x + 196y + ¼u - ½w = 83,588

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  Kaikoura), 186x - 8y + 9/4u - 3/2w = 8,665

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  Wellington), 384x - 16y + 9/4u - 3/2w = 36,928

• Nelson), 300x + 110y + 9u - 3w = 25,525

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Hence x = 145·15 miles, y = 59·6 miles, v = 493/4 miles per minute = 4,378ft. per second (velocity of propagation), and the time at the origin = 8h. 1min. 20sec. A.M. The point K near F, five miles and a half W.S.W. of Nelson, is the point thus found for the epicentrum. By trial we find that a depth of about 5 miles for the centrum best suits the data.

This agrees within the limits of errors of observation with Westport, and also with Wanganui, if we take the mean of the two observations (both by good observers).

The degree of agreement is shown by the time at the origin as calculated back from each place; it should be the same, of course, from whatever place we reckon.

The other places do not give a time at the origin agreeing with this; but the errors are all (or very nearly all) of one sign, and vary from-1min. to - 3·96min., occurring in groups. Examination of the several groups leads us to suppose that there were several shocks, all nearly below K, the first deep, about 25 miles down, the second higher up, and the third about 5 miles below the surface. At some of the more distant

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places only the deep-seated shocks were felt. At Wanganui Mr. Field noted vibrations for 4 or 5 minutes with several distinct shocks (but possibly several maxima of the same shock). At Timaru the first shock, and a later one (about 11/2 or 2 minutes later), were observed. Of all these positions found for the epicentrum, E2 best corresponds with the Nelson observations of direction; but it is possible that, if these observations were those of the transverse vibrations, K, or a place a little to the north of it, would agree equally with them.

It is, of course, most likely that the epicentrum would be an area large enough to include all the places, K, F, E₂, E₂ (epicentric area on map, PI. XLI.). The amount of damage done at Nelson was greater—far greater—than that reported from any other place. It is probable, therefore, that the angle of emergence there was nearly that of the maximum intensity—i.e., between 56° and 45°. This would agree with either K or E2, with a depth of 5 miles for the origin.

The origin might be guessed at with a tolerable degree of probability by the use of isoseismals. Looking at the last column in the table given above, we see that the isoseismal of intensity, vii. on the Rossi-Forel scale, would be drawn outside Picton, Takaka, Collingwood, Wellington, Blenheim; but would have all the other places outside it. An ellipse might be so drawn with a focus not far from the epicentric area (K, F, E3, E2).

3. Intensity.—The maximum intensity of this earthquake was as far above the average of our ordinary mild New Zealand shocks as its velocity of propagation was. The intensity at Nelson was evidently viii. (Rossi-Forel scale), or a little above it.

If a = amplitude of the largest vibration in the motion of any earth-particle, and T = the period of the largest wave, then 4π²a/T² = intensity of shock defined mechanically = destructive effect = maximum acceleration due to the impulse.

Now, Dr. Holden, Director of the Lick Observatory, has given equivalents of the degrees of earthquake-shocks on the Rossi-Forel scale in terms of the acceleration due to the velocity of the shock itself (American Journ. Sci., 1888, No. 210).

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Thus a shock of intensity viii. corresponds to 500mm. per second. We should not probably be far wrong if we gave 600mm.-800mm. per second as the measure of the intensity of our present earthquake—or, in other words, from 1/16 to 1/12 of the acceleration due to gravity.

Summary.—The earthquake of the 12th February; 1893, originated below an area within 5 or 6 miles of Nelson, 23

the left side have been turned round so as to expose their inner surfaces. Portions of four pectoral ribs are seen near the right coracoid. Behind these vertebræ are the pubes and ischia, which have been but little displaced. Those on the left side are nearly perfect, but those on the right side have lost their outer margins. Behind the pelvic arch is the tail, the four teen vertebræ of which have been split longitudinally in section, so that no surface is seen. Anteriorly these vertebræ present an indistinct mass, but the last seven on the slab show distinct outlines. Here the specimen ends abruptly, but it is evident that the tail must have been continued much further, as it tapers but little. The transverse breadth of the last vertebral centrum is 55mm., while the largest lumbar centrum has a transverse breadth of only 65mm. These caudal vertebræ, being in section, show that the articular surfaces of the centra are more deeply concave than in most of the plesiosaurs; and the same can be ascertained for the trunk vertebræ by removing a portion of two of the centra.

In the abdominal region, just in front of the pubes, there are a number of rounded pebbles of quartz—about seventy-five can be seen—varying in size up to 20mm. in diameter. As similar pebbles are not found elsewhere in the rock containing the saurian remains, it is evident that these have been swallowed by the animal, probably to adjust the specific gravity of its body with that of the water.

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The total length of the specimen is 5ft. 21/2in., of which the tail occupies 1ft. 8in. The distance from the post-axial margin of the coracoid to the pre-axial margin of the pubis is 1ft. 8in., and the greatest antero-posterior length of the pelvic arch, from the pre-axial margin of the pubis to the post-axial margin of the ischium, is 1ft. 1in. The animal was about the size of Plesiosaurus australis, to which it was referred by Sir Julius von Haast; but Sir James Hector pointed out that it does not agree with that species either in the shape of the ribs or in the form of the vertebral centra, and he considers that “it must have been a very different animal.”^* The pelvic bones also differ much from those figured by Sir James Hector. In the distinctly but moderately cupped articular surfaces of the vertebral centra this specimen resembles P. crassicostatus and P. hoodii alone of the described New Zealand sauropterygians; but in both those species there is a tubercle in the centre of the cup, which does not appear here, and they both have the centra proportionately shorter than in the present specimen. The proportions of length to breadth of the vertebral centra resemble those of P. mackayi and

and 55mm. in the most posterior. The cups are simply concave, without any flattening or tubercle in the middle. The chevron bones were not anchylosed to the centra. One of these (Pl. XLII., fig. A, c.v.), lying on the surface alongside the vertebra which is the last but two in the series, is 40mm. in length, and the two limbs are 28mm. apart at their ends. Two others are seen lying on their sides, each being 43mm. in length and 14mm. in breadth. As the ventral surfaces of all the caudal vertebræ are missing, it is impossible to say whether these chevron bones were or were not attached to the centra by longitudinal ridges.

Ribs.—The shafts of four displaced pectoral ribs (p.r.) are partially exposed on the right side of the animal at and just below the coracoid. They are thick and strong, and slightly compressed, their diameters being about 20mm. and 16mm. Several abdominal ribs (a.r.) show on each side, and these are but little displaced. They are more slender than the pectoral ribs, their diameter being only 13mm. The external surface is rounded and longitudinally striated, while the internal surface is flattened, and has a deep and broad longitudinal groove.

Pectoral Arch.—The coracoids (co.) are but slightly displaced, and the two still touch each other anteriorly. They are longer than broad, deeply notched in front, concave on the outer margin, and convex on the posterior margin. The inner margin is also apparently concave. I am aware that in the plesiosaurs the coracoids are often thin and broken in the middle, but that is not the case with this specimen. In it the inner margins are smooth and rounded, and that of each coracoid is symmetrical with that of the other, which could not be the case if they were broken. Consequently the coracoids must have been separated by a large fontanelle in the middle, and have touched anteriorly and posteriorly only, as represented in the diagram (PI. XLII., fig. B). At the anterior symphysis the bone curves ventrally so as to make a longitudinal keel with its fellow. The inner anterior corner is broken, and we cannot say how far it projected forward, or whether it articulated with a pro-coracoid. The antero-posterior length of the coracoid is 10·5in. Its anterior breadth, from the posterior end of the glenoid cavity, is 6·5in. its posterior breadth is 5in., and the breadth in the middle is 2·5in. Only the post-axial extremity of the scapula-remains, and it is too fragmentary to afford any reliable characters. The proximal end of the humerus is 2·5in. in diameter, and at a length of 3·5in. from the end it has expanded to a breadth of 4·5in. This end of the humerus is not well preserved, and it cannot be ascertained whether it bore any trochanterial ridges.

Pelvic Arch.—This is but slightly displaced, and better

denuded surface of the Palæozoic sandstones and greywackes, while no elastic rocks of younger date are found overlying them.

The scarcity of evidence relating to the age of these tuffs is a noticeable feature of the geology of the Hauraki Peninsula, and this circumstance is solely due to the almost entire absence of members of the numerous fossiliferous formations which in other parts of New Zealand render the geological structure so varied, and very frequently so involved and complicated.

The only evidence bearing directly on the age of these rocks, so far as known at present, is found at Waitete, situated on the coast-line a few miles south of Cabbage Bay. Two years ago, when making a reconnaissance geological survey of that part of the coast, I discovered a small patch of the New Zealand brown-coal measures, occupying an area not many square chains in extent. They consisted of the following strata, reading the section downwards:—

• 1. Hard shelly limestone.

• 2. Calcareous and marly sandstones.

• 3. Ferruginous conglomerates.

The conglomerates were about 200ft. thick, and rested directly on the basement rocks, which at this point consisted of blue- and red-banded slaty shales. The shelly limestone, which was the highest and closing number of the series, dipped away to the north-east, and a few chains back from the beach disappeared below a great accumulation of volcanic tuffs, breccias, and solid lava-flows of an andesitic character. These rocks, so far as could be judged from physical characters and general appearance, were in every respect similar to the gold-bearing tuffs and associated rocks in other parts of the peninsula.

On a subsequent occasion I traced these tuffs and breccias without a break as far as Paparoa and Paul's Creek, and thence southwards to the Tokatea Range near Coromandel. Another circumstance which tends to prove their identity with the tuffs and andesites of the Thames and Coromandel is the discovery in them of gold-bearing veins of quartz in the neighbourhood of the limestone deposit.

The Palæozoic rocks on which the coal-measures rest are in several places in the vicinity of Waitete intruded by massive dykes of igneous rock. It is a noteworthy fact that I was unable to find, after a most careful examination, a single fragment of igneous rock included among the materials composing the conglomerates. This negative evidence is of great value as tending to prove that these igneous intrusions took place after the deposition of the Cretaceo-tertiary coal-beds. The whole of the stratigraphical evidence obtainable at Waitete

seem bold to invoke the aid of such a vast explosion, we must remember that even in recent times there have been cataclysms that have equalled in intensity and magnitude that required for the formation of Lyttelton Harbour. The force expended at the Krakatoa eruption was quite as great as that required by hypothesis in the present case. Even in New Zealand we have had an illustration of the immense power exerted by imprisoned steam in the destruction of the terraces at Rotomahana, where a gigantic chasm was formed almost as large as Lyttelton Harbour.

Since this great spasmodic effort two other eruptions or periods of activity have been witnessed in this system. The first resulted in the formation of Mount Herbert in the former caldera wall, where the lavas which flowed down the sides of this secondary vent interfere with the symmetrical appearance of the walls.

By the last eruption Quail Island was formed. This eruption is unimportant; it does not seem to have been attended by any explosive action, and to have attained to only extremely small dimensions.

As would be expected from the spasmodic character of the earlier eruptions, a large number of radiating cracks were torn open in the surrounding crater-walls, and into these the magma was injected, giving rise to a well-defined system of dykes, which preserve an astonishingly constant direction, width, and composition over large horizontal and vertical distances. From a careful examination of these dykes it was ascertained that, with a few exceptions, they can be classed in two systems. Of these the most important radiates from a spot situated a little to the south of Quail Island, while the other proceeds from the centre of a shallow bay to the south-east of the former one.

The rocks of the Lyttelton system are, with a few exceptions, members of the basic series of igneous rocks, the commonest species being one that is best named olivine-andesite. Andesites without olivine have also been found, while basalts, especially in the later eruptions, are frequent, being, as a rule, very finely grained. Trachytes also occur, particularly in dykes, and from the prevalence of dykes of trachyte Sir Julius von Haast drew an important induction in support of Durocher's theory of volcanic action and the origin of the eruptive rocks. Rhyolites are also found as members of the very earliest eruptions, and still crop out at Governor's Bay, on the shore of the harbour.

The most anomalous of all the rocks occurs on the Lyttelton-Sumner Road, about half a mile from Lyttelton. This rock was discovered by Sir J. von Haast, and was called by him a domite. A chemical analysis was made by Professor Bickerton,

which is quoted on page 300 of Haast's “Geology of Westland and Canterbury.” Subsequently the rock was examined by Professor Ulrich, and he discovered the rare mineral tridymite in it. Specimens were also sent to Professor Von Rath, but no detailed description of the rock has yet been published, though a collection of volcanic rocks was described in Germany.

Professor Von Haast, in the “Geology of Canterbury and Westland,” describes this rock as “a remarkable trachyte rock, interstratified between two others of a basic character.” He thus evidently considers that it comes from the same source and has the same origin as the other rocks of the Lyttelton system. After a careful examination of the rock itself and the surrounding lavas, the writer has been forced to form an opinion directly opposed to the expressed and written ideas of the professor.

As it would be impossible to give an intelligible description without the aid of a diagram, part of an official chart of the harbour and an enlarged rough sketch-map of the area examined are added (Pl. XLIV.). In the chart it will be found at the point A. The chart has a scale of 1 ⅔in. to the mile. The sketch-map is intended to show only that part of the district that has been actually examined.

About half a mile from Lyttelton the Lyttelton-Sumner Road passes an abrupt wall of a whitish rock, K, about 30ft. high, extending about 70 yards up the face of the hill and a few yards below the road, the wall being nearly at right-angles to the direction of the road. As it is followed up the hill this wall gradually decreases in height, and is ultimately on a level with the surrounding ground. Higher than this the outcrop cannot be traced at this point, but it turns sharply to the right, and runs for some distance parallel with the road. The highest point of this outcrop is about 490ft. above sea-level. Between this height and 690ft. the slopes are thickly covered with grass, except in one or two places where basic lava that apparently overlies the trachyte crops out. At a level of 690ft. above sea-level there is another wall-like outcrop, which runs almost parallel to the direction of the road, and is fairly constant in elevation. To the right it gradually gets smaller, and disappears at C. On the left it ends somewhat abruptly at D. From this point to the top of the hill, 770ft., all the rock seems to be trachyte of the same character as the first outcrop, and its resemblance is borne out on microscopical examination. At E, along the crest of the hill, the trachyte seems to disappear, and a little further on a wall-like buttress of basic rock stretches across at right-angles to the axis of the hill. Descending the hill from E to F, the ground is strewn with boulders of the same rock; and at F, on the

shore of the harbour, there is a small cliff of the same rock, with several small sea-worn caves. The cliffs continue to bound the shore to the point H, whence it slopes up the hill to K, which was our starting-point.

There are four well-defined dykes in this rock, three of which, M and N, on the shore, are of small size, while the fourth, which cuts into the outcrop K, is 6ft. to 7ft. wide.

At the top of the hill there is clear evidence of a large dyke, which runs parallel to the length of the hill, along its summit. In breadth the dyke measures about 20ft., and in length about 200 or 300 yards, its bearing being E. 41° N.

It is evident that the trachyte lava issued from this dyke, as outcrops are found the whole way from the top to the bottom, and are generally of a vesicular character. If, as Sir J. von Haast suggests, it flowed from a central crater, situated near Quail Island, it would necessarily, like the other rocks of the harbour, present a single face of moderate breadth, and of a tolerably constant altitude above the sea-level.

It is possible that the lava flowed from a crater that occupied the position where the Town of Lyttelton now stands. This, however, is highly improbable, as no independent evidence exists of the activity of a vent situated there. No system of dykes has been discovered; none of the other hills enclosing the depression afford evidence of such a vent, while on one side all traces of crater-walls, if they ever existed, have been removed.

The very appearance, too, of the hill under consideration gives one the idea that its origin is not the same as that of the others, for, while its surface is, generally speaking, smooth and rounded, and resembles the slopes of Mount Herbert, the others, almost without exception, present that series of sharp, steep walls rising tier above tier that so plainly indicates to the geologist that they are formed of lava-flows lying one over the top of another with a moderate angle of inclination. These considerations, and the fact that a well-defined dyke exists at the summit, must remove all doubt as to whether an independent origin should be assigned to this small system of volcanic products.

As the age of the whole system of Banks Peninsula is not yet settled with any exactitude, it would be idle to attempt to ascertain the precise geological age at which this minor eruption took place. There is, however, little difficulty in ascertaining its age relatively to the other eruptions of this volcanic system.

It is stated by Sir J. von Haast that the original crater was the only one whose eruptions were of a sufficiently spasmodic character to rend fissures in the surrounding rocks, which, on being filled with igneous matter, form dykes.

Now, it is evident that this large dyke must have been formed during or preceding such a paroxysmal eruption. Its age, then, must be assigned to some period during which these eruptions were still in full force. Again, it is evident that the caldera of Lyttelton had already been formed when this eruption took place, for the lavas that were emitted from this dyke flowed down the face of the harbour-walls when they were approximately of their present shape and form, otherwise during the formation of the caldera this small accumulation would have been blown out of existence. Thus its age can be assigned as not earlier than the latest phase of eruption.

Lastly, the presence of other dykes piercing this rock proves that the convulsion by which the large dyke was formed was not the last effort of the declining volcano, but force still resided in it sufficient to crack the surrounding rock, and volcanic magma was still present in sufficient quantity and under sufficient pressure to fill these cracks up to the level of the surface, and thus form dykes.

The age, then, of the system must be stated as younger than the most violent paroxysms of the central volcano, but in all probability older than the Mount Herbert system, for these lavas are in no place seen to be pierced by dykes, and the eruption was therefore subsequent to the convulsions of the central crater.

The presence of sea-worn caves even near the top of the hill does not help us much, as it has been shown by Professor Hutton and others that within the Pliocene period great oscillations of level have taken place.

In macroscopic appearance the trachyte previously mentioned resembles a rhyolite in its very light colour, but no quartz crystals can be seen.

The colour is almost white in places, but generally iron-oxide has segregated in cracks owing to weathering, thus giving it a banded and sometimes almost spherulitic appearance.

Large crystals of plagioclase can be distinguished, the striation often being visible with a simple lens. The rock is generally vesicular, and it is in these vesicles that glass-clear tridymite crystals are seen, and frequently appear to have a hexagonal outline.

The texture is porphyritic, the phenocysts being invariably feldspars.

There are two well-developed divisional planes in the rock, one being parallel to its surface and the other parallel to the direction of flow, showing that the cooling proceeded from the surface as well as from the sides.

No macroscopical difference can be seen between the rock on the summit of the hill and that on the sea-level, except

that the former is, if anything, the more vesicular of the two.

The mineralogical structure of this rock presents many peculiarities, both in the nature of the minerals themselves and in their association with one another.

Tridymite occurs in considerable abundance, for, although thirty-six sections of the rock were cut, some crystals of the mineral occur in every section. The feldspars, both ortho-clastic and plagioclastic, frequently occur in large porphyritic crystals, and present the peculiar feature of a central core of plagioclase surrounded with a mantle of orthoclase or sanidine. Ferro-magnesian constituents are rare, or entirely absent, but magnetite occurs in considerable quantity, while needles of apatite penetrate the ground-mass and feldspars. As an accessory of somewhat doubtful occurrence, zircon may be mentioned.

Tridymite, although often present in the ground-mass, is generally found attached to the sides of vesicular spaces, and sometimes completely fills the smaller vesicles. The crystalline groups are, as a rule, of irregular shape, but in some a fairly regular hexagonal boundary may be observed. They are quite transparent, and possess a vitreous lustre.

In sections they appear generally as rounded aggregates, quite clear and transparent, with numerous cracks that resemble cleavage. With polarised light, however, they break up into a number of irregularly-shaped areas of extremely minute dimensions, but all possessing different optical orientation. To see the structure distinctly, a magnifying-power of 70 diameters or more should be employed, and it will then be noticed that, although irregular, there is an approach to the hexagonal boundary in the majority of the plates. Each of these areas undoubtedly represents a distinct individual, but, owing to their extremely small dimensions, it was found impossible to isolate any one of them and submit it to optical examination with the hope of forming any ideas as to the system of crystallization. The peculiar irregular structure of the aggregates is well shown by altering the focus of the microscope by means of the fine adjustment, when it will be seen that, even in the thinnest sections, there are several layers of crystalline plates.

The aggregates are frequently traversed by cracks which seem to bear no definite relation to the outline of the individual grains of the aggregates themselves. A peculiar feature of many of these grains is a radial structure (shown in Pl. XLVIII., fig. viii.). Although not universal, this structure occurs in the majority of the grains. Figs. vii. and viii. were both drawn from a section beneath a magnifying-power of 70.

Fig. vii. shows the normal structure of tridymite with polarised light, except that the different areas are not shaded as they appear beneath the microscope. The interference colours are always low, but it was found impossible to give the general effect by shading the different areas.

Feldspars.—These are perhaps the most interesting of all the minerals in this rock, for the sections serve to show that the isomorphism of orthoclase and the more acidic plagioclases (andesine) is almost exact—so nearly so that crystallization of sanidine can proceed with as great energy round a core of plagioclase as round one of sanidine.

Sanidine occurs in beautiful glassy porphyritic idiomorphic crystals, as well as in granular aggregates with irregular outlines. The porphyritic crystals are generally of small dimensions, and often give square sections, which shows that the crystals are not generally elongated in the direction of the chief axis. Cleavage is plainly seen in most of the sections, and a faint zonal structure can generally be observed. Between crossed nicols the interference colours are low, greys and bluish-grey of a low order being general, and affording a marked contrast with the brilliant interference colours of plagioclase in the same section.

Twinning is exceedingly common, and, though well-developed examples of the Carlsbad type are frequent, the majority of the twins are irregularly penetrating, frequently without the slightest indication of any regular law; but at other times twins resembling those formed on the Baveno and Manebacher law have been observed.

The Carlsbad twins—composition plane ∝ ρ ∝ (010), twinning plane ∝ ρ ∝ (100)—are numerous, occurring in crystals of all sizes, even the microlites in the base sometimes showing this type of structure. Some examples of these twins are given in the figures.

A twinned crystal that bears some resemblance to a Baveno twin is shown in Pl. XLVIII., fig. ix. Unfortunately, this crystal seems to have been considerably corroded before the rock cooled, and the margin has therefore become somewhat rounded. Supposing this to be a Baveno twin, it would consist of four individuals such as those figured in Dana's “Textbook of Mineralogy” (page 100, fig. 325, and page 325, fig. 587). The composition and twinning-plane are the clinodome 2 ρ ∝ (021). Although the traces of the twinning-planes are not exact diagonals, they do not show more irregularity than many of those of the Carlsbad twins. A very similar crystal has been found in another section; while in a third there is another, consisting of two individuals, the twinning trace being more nearly a diagonal.

Irregular penetrating twins are frequent, and some are

drawn in the annexed figures. They do not call for any special description.

In order to show clearly that the supposed sanidine is not plagioclastic feldspar cut in the direction of a plane parallel to the brachypinacoid ∝ ρ ∝ (010), Pl. XLVII., fig. v., may be mentioned. In the large crystal drawn in this section the traces of the faces which appear longest have cleavage-cracks parallel to them, and must therefore be the traces of the base O P (001) and the clinopinacoid ∝ ρ ∝ (010).

As these traces are almost exactly at right-angles to one another, and extinction takes place when the cross-wires are parallel to these traces, the section must be cut in the zone of the orthopinacoid and base. If, now, the mineral were plagioclase, twinning parallel to the brachypinacoid (corresponding to the clinopinacoid of sanidine, as shown below) would be observed in such a section—that is, supposing the usual isomorphic relations to hold good, as they will be shown to do when the plagioclases are considered. The fact that the mineral extinguishes parallel would in itself generally be considered sufficient to show that it is sanidine and not plagioclase. The truncations of the angles are, of course, due to the development of a clinodome. The same method of reasoning may be applied to fig. vi., Pl. XLVII., where there is a core of plagioclase surrounded by a broad rim of sanidine. This example is even more conclusive than the last, as here the plagioclase is twinned on the albite type, and it cannot therefore be pleaded that the mineral is untwinned plagioclase. Since sanidine is doubtless present in this crystal, it may be said with safety that the other unstriated feldspar possessing similar interference colours is sanidine.

Plagioclase is also present in crystals with idiomorphic outlines, and generally of a far larger size than the crystals of sanidine. Almost invariably, however, there is an investing mantle of sanidine, which sometimes is of far larger diameter than the core of plagioclase, but in other cases far smaller. In general, the plagioclase can hardly be called idiomorphic, as it passes in many cases gradually into the surrounding sanidine, the exact boundary-line being hard to determine. Occasionally, as in Pl. XLVI., fig. iv., there appears to be an outer zone of plagioclase possessing different optical orientation from the inner one. Cleavage-cracks can seldom be seen, and zonal structure is rare and inconspicuous when developed.

Twinning is splendidly developed, according to three well-defined laws—Carlsbad, albite, and pericline. The Carlsbad twins are exceedingly common, the two halves being frequently as sharply defined as in sanidine. The investment of sanidine, in every observed case but one, is also twinned, but its orientation is different from that of the plagioclase, although the

composition plane is a continuation of that of the plagioclase. Since these two planes are coincident, the plane of twinning on the Carlsbad type in the plagioclase must be parallel to the clinopinacoid in the sanidine. But the twinning-plane of the albite lamellæ is parallel to the twinning-plane of the Carlsbad twins, and, as, according to the albite law, the lamellæ are twinned parallel to the brachypinacoid, it is evident that the composition plane of the Carlsbad twins is also the brachypinacoid. Hence in these crystals the clinopinacoid of the sanidine corresponds with the brachypinacoid of the plagioclase. The Carlsbad twins in the plagioclase show the same irregular intergrowth that forms a noticeable feature in the sanidine.

Albite twinning is exceedingly common, the lamellæ varying greatly in width, but on the whole they are narrow, the width being constant throughout their length. In a few cases the lamellæ are curved or broken, and possess undulose extinction, thus showing that the rock was subjected to considerable pressure or tension previous to its extrusion.

If a section of plagioclase is cut at right-angles to the brachypinacoid the extinction of the adjacent lamellæ of the twins would make equal angles on each side of the cross-wires. Although in the sections none of the plagioclase crystals are cut precisely in this direction, some of the surfaces coincide approximately with such a plane.

The following have been measured:-

These results, although rather high, tend to show that the species of plagioclase is andesine, a conclusion that will subsequently be shown identical with that derived by chemical analysis. It was found impossible to detach cleavage-flakes, so that the extinctions on the base or brachypinacoid could not be determined.

Twinning after the pericline law (twinning-plane the “rhombic section”) is not nearly so frequent nor so well developed, the lamellæ being as a rule of variable length, frequently not traversing the whole breadth of the crystal, and leaving untwinned feldspar between the adjacent twins.

Plate XLVIII., fig. x., shows a crystal where this type of twinning is seen in combination with twinning after the albite law. The drawing is a faithful representation of the crystal as

it appears between crossed nicols when the longer side of the crystal is inclined at an angle of 33° with the cross-wires. It would appear that h, e, d are broad lamellæ of pericline twins, n being a tongue of feldspar twinned on the albite law, the lamellæ appearing on rotating the stage. The lamellæ h, e, d are themselves striated with albite lamellæ, which also appear at e, c. The lamella d, on the other hand, has subsidiary striation due to twinning on the pericline law. c d, e f, all extinguish together, as do n h; mm are grains of magnetite. The whole is surrounded with a mantle of sanidine, a a.

Magnetite is present in every section, but varies considerably in abundance. The grains exhibit great variation in boundary, as the usual form of the mineral is the rhombic dodecahedron and octahedron. Some grains show a fairly regular hexagonal boundary, and it is possible that ilmenite, which crystallizes in the hexagonal system, is present.

Augite is of doubtful occurrence, for though between thirty and forty sections have been cut there is no single occurrence of this mineral which cannot be questioned. One section shows an opaque crystal with octagonal outline, which is probably a section of augite in which both prisms as well as pina-coids are developed. As, however, almost the whole of the crystal has been changed into iron-oxide, its optical properties cannot be investigated.

Apatite is present in numerous prismatic needles which pierce the feldspar and ground-mass, and was therefore the first mineral to crystallize out of the magma.

Zircon seems to be represented in one slide where there are two short prismatic crystals terminated by obtuse pyramids, and possessing straight extinction as well as strong double refraction, indicated by brilliant colouring between crossed nicols. It would, however, be rash to assert from these isolated examples that zircon occurs in the rock, especially as it has been found in no other slides, including those prepared by Professor Ulrich.

The ground-mass of the rock is composed of feldspathic microlites, tridymite, and magnetite, and in rare instances there are globules of a greenish glass. Beneath, the quarter-inch objective it cannot be determined to what species of feldspar these microlites belong, but, since sanidine has in the porphyritic crystals evidently crystallized subsequently to the plagioclase, we have a certain amount of right to infer that the microlites consist chiefly of sanidine. Irregularly-bounded tablets of tridymite will be observed in very thin sections to occupy a large portion of the ground-mass, but in thicker sections they are frequently over- or underlaid by microlites. It will be shown afterwards that a large proportion of the base must consist of tridymite.

Iron-oxides (magnetite, and sometimes hæmatite) are frequent in small specks without crystalline boundaries. Hæmatite, with a little limonite, is particularly abundant in cracks, and in all probability results from the further oxidation and hydration of the magnetite.

Beneath the highest power of the microscope (700 diameters) no isotropic matter indicating the presence of interstitial glass can be seen, but occasionally, especially from the vesicular upper surface of the lava-flow, there are inclusions of a greenish glass in globules of a spheroidal form, the structure in one or two cases being almost pisolitic.

A few of the sections were examined in convergent polarised light, and the following results were obtained:—

The large crystal in Pl. XLVII., fig. v., shows two hyperbolic brushes which meet almost in the centre of the field, and the section must therefore be cut almost exactly at right-angles to an axis of elasticity. Since in such a thin section both hyperbolas appear, and when furthest apart they barely disappear from the field, the axis of elasticity must be the acute bisectrix. With the quartz wedge the hyperbolas are far more widely separated, and the result therefore is equivalent to the thinning of the section, which shows that the optical signs of quartz and sanidine are opposite, and since quartz is positive the acute bisectrix in sanidine is negative. Further, since the section was shown to be cut in the orthopinacoid-basal zone, the acute bisectrix must be at right-angles to the orthodiagonal.

The acute bisectrix is thus shown to be negative, and at right-angles to the orthodiagonal, a result in accordance with the general optical properties of sanidine or orthoclase (Dana's “Text-book of Mineralogy,” p. 325).

Plate XLVII., fig. vi., in convergent polarised light only shows one hyperbola, and is therefore not cut at right-angles to an axis of elasticity, although it is cut perpendicularly to the plane of the optic axes.

In convergent polarised light tridymite only shows faint indications of hyperbolic brushes, which appear only in the edges of the field.

Plate XLVIII., fig. ix., the supposed Baveno twin, gives uniform phenomena all over the crystal as far as can be seen, but, as it is not cut at right-angles to an axis of elasticity, this is not certain, as the brushes merely sweep across the section apparently in the same direction in all parts of the crystal. This militates considerably against the supposition that the crystal is a Baveno twin.

Chemically, this rock presents rather peculiar features, as will be seen from the following analysis. The first two analyses are of the same specimen, while the other

three are of another specimen, collected from an adjacent locality:—

The large percentage of silica combined with such, a considerable percentage of lime is a very unusual feature, but would be expected when the large amount of plagioclase is taken into consideration. The excess of silica over and above that required for combination with the bases is of course present in the mineral tridymite. The analyses tend to show that the feldspar present is chiefly a species of plagioclase—i.e., a soda-lime variety—and this is confirmed by optical examination.

The presence of manganese was indicated by the bluish-green colour of the fusion mass, but this was not strong enough to warrant a special quantitative determination.

The percentage of magnesia shows that some ferro-magnesian mineral is present in small quantity, but microscopical examination shows that they are practically absent. Some of the larger accumulations of iron-oxide may possibly indicate the former presence of some ferro-magnesian mineral which has been re-fused owing to the relief of pressure, or some other changed condition subsequent to its original crystallization.

Phosphoric acid is of course accounted for by the presence of apatite crystals. No test was made for this substance in the last-three analyses.

In the first two analyses the iron was all converted to the ferric condition before precipitation, and no determination of ferrous oxide was made.

From these analyses a rough approximation may be made as to the amount of free silica present in the form of tridymite, for, assuming that all the potash is in combination with silica in sanidine, and all the soda goes to make up the plagioclase (andesine), the excess of silica over that required

for these combinations will be present as tridymite, as no interstitial glass has been detected.

Taking the average composition of sanidine as that given in Dana's “Text-book of Mineralogy,” we find that it contains 16·9 per cent. K₂O and 64·7 per cent. SiO₂. In a rock containing 2·46 per cent. K₂O, 9·42 per cent. SiO₂ would be required for combination. Again, CaO and Na2O make up 14·7 per cent, of andesine, while the percentage of silica is 59·8. Assuming that Na₂O and CaO are to a limited extent mutually replaceable in the andesine molecule, and taking the molecular weight of Na₂ (46) as equivalent to that of CaO (40), we have in this rock 8·06 per cent, of these bases, and they would require 32·60 per cent, of silica for complete saturation. Altogether, then, 42·02 per cent, of silica is required for combination, and the remaining 29 per cent, will be represented by tridymite. As, however, a very small proportion of the rock as seen in section is tridymite, it is fair to assume that a considerable amount must exist in the ground-mass.

As tridymite is stated to be soluble in caustic soda (Rosenbusch: “Microscopical Physiography of Rock-forming Minerals,” translated by Iddings, p. 174), an attempt was made to estimate its percentage by taking advantage of that fact: 29·95 per cent. SiO2 was dissolved out of the rock, but, as 15·05 per cent. Al₂O₃ was also present in the solution, the result is not satisfactory.

An analysis was also made of the feldspar, but it was found extremely difficult to isolate an appreciable quantity, and the result of the analysis cannot be considered strictly accurate:—

The result is almost the same as would be expected on consideration of the bulk analysis of the rock, except that the percentage of K₂O is rather high. Sanidine forms only a small border round the relatively large crystals of plagioclase that were the only ones obtainable for analysis.

No attempt was made to determine the species of plagioclase by means of its specific gravity, as the difference in this physical quantity between two closely-allied species of plagioclase is extremely small, and would be completely masked by the lower specific gravity of the mantle of sanidine. An approximate correction for this would give an eminently unsatisfactory and wholly unreliable result. The same applies to Szabo's flame reactions.

Although fully recognising the danger of theorising upon any subject when the data are insufficient, I cannot refrain from offering a suggestion as to the cause of silica crystallizing in the form of tridymite. The available data to reason upon are—

• 1. The invariable presence of tridymite in cavities;

• 2. Its frequent radial structure;

• 3. Its non-inclusion in other crystals.

All these point to the conclusion that the mineral was deposited subsequently to all the other minerals of the rock, and from a solution in some solvent. Silica if uncombined is well known to be insoluble in pure water at atmospheric pressure; but there seems to be every reason to suppose that it is soluble in water above its critical temperature and under considerable pressure. The experiments of Daubrée with water in glass tubes confirm this, and the theory to account for the fact that quartz is the last mineral to crystallize in granite shows that it is generally believed that silica can be dissolved in water of a sufficiently-high temperature and under great pressure. In lava, prior to its extrusion, the water present would probably be capable of dissolving silica, but on the eruption of the lava the pressure would be suddenly relieved and the temperature quickly lowered, and consequently the silica would be precipitated. Owing to this rapid precipitation the silica molecules might be unable to arrange themselves in their ordinary arrangement, or the molecular forces, owing to direct solution or the subjection to heat, might well be different from the ordinary molecular forces, and would tend to form a different geometrical solid from that formed under the normal conditions.

That the molecular forces under certain conditions are liable to variation is well shown by the production of dimorphous forms in Ca CO₃, native sulphur, and other minerals; and there seems to be no physical reason why variation should not exist in the case of others when the conditions accompanying crystallization also vary.

The extreme minuteness of the individual crystals would seem to indicate rapid precipitation, while inclusions of steam or other fluids would easily find their escape through the divisional planes between the different crystal plates.

It does not seem probable that high temperature alone, or sudden cooling, determines the system in which silica crystallizes, since in rhyolites and other lavas in which these conditions obtained the silica crystallized in the form of quartz. In the case of holocrystalline rocks, on the other hand, the cooling was extremely slow; and in the case of older lavas the molecules may have had time to readjust themselves in accordance with the normal forces after extrusion. In recent lavas

containing quartz the absence of tridymite may be explained on the hypothesis that steam was not present in sufficient quantity or of a sufficiently high temperature or tension to dissolve the silica.

The juxtaposition of sanidine and plagioclase can easily be explained by assuming that under like conditions the molecules of plagioclase would have greater tendency to accumulate than those of sanidine, and the plagioclase would accordingly tend to crystallize first. With slightly-changed conditions sanidine might also crystallize, and because of the almost complete isomorphism existing between it and plagioclase it would crystallize round the already-formed core of plagioclase.

Possibly there is a gradual increasing acidity in the plagioclase from centre to margin, as well as a gradual change from the base Na2O to K2O. This would better explain the presence of the mantle of sanidine, for during crystallization there would not only be a gradual increase in acidity in the successive layers, but also a corresponding gradual change in crystalline form. The centre of the core of plagioclase might then be very basic, while the outside rim might be acid sanidine. The occasional presence of an intermediate differently-oriented layer of plagioclase between the central core and the sanidine lends this view considerable support. Again, the boundaries of the plagioclase very seldom show that sharp definition that would be expected if the change was sudden; and frequently there appears to be no actual line where the plagioclase ends, but it appears to pass laterally into the sanidine.

The nomenclature of the rock presents considerable difficulty, for it seems to form a connecting-link between three classes of lava.

If classification according to percentage of silica is adopted, the rock must be classed with the rhyolites or liparites, though the presence of quartz crystals is generally adopted as a specific character.

If Rosenbusch's classification is adopted, we should hesitate as to whether the rock should be called a trachyte or an andesite, the distinction hinging mainly on the preponderance of sanidine over plagioclase, or vice versâ; and as, according to analysis, the latter appears to be in excess, the rock would have to be classed with the andesites.

According to its mineralogical composition, a place might be assigned to it among the dacites; but, at the same time, tridymite would have to be considered a mineralogical equivalent of quartz. The absence of any ferro-magnesian constituent must, however, tell largely against its inclusion in this class.

The name tridymite-dacite would give the idea of presence of free silica, as well as the preponderance of plagioclase over sanidine, but would imply the presence of augite or hornblende. On the other hand, the feel of the rock, its specific gravity, the absence of a glassy base, and its very light colour, as well as, to a certain extent, its highly acid composition, all tell largely in favour of its being pronounced a trachyte; and I have therefore preferred to call it an andesine-tridymite-trachyte, the two pronomens being used to indicate its exceptional mineralogical characters.

In order to demonstrate the relations of the neighbouring rocks to this trachyte, several sections have been cut and some analyses made of the lavas that appear to have, proceeded from the same orifice, as well as of the intrusive dykes and other neighbouring rocks.

Immediately underlying the trachyte, and undoubtedly proceeding from the same vent, is a black lava that resembles pitchstone except for large porphyritic crystals of feldspar. Cavities are fairly numerous, but not so abundant as in the overlying rock. Sp. gr. 2·46.

Under the microscope there are large idiomorphic crystals of sanidine, and occasionally plagioclase surrounded by sanidine, as in the overlying rock. The sanidine is generally twinned on the Carlsbad type, some splendid crystals of this twin being obtained. The plagioclase is twinned after both the albite and Carlsbad laws, but does not present such interesting or marked combinations as in the overlying rock.

Augite of a bright-green colour occurs in idiomorphic crystals, generally of small size, as well as in microlites. It is slightly dichroic, but calls for no special mention.

Magnetite and apatite are present in fair abundance. The ground - mass consists of microlites of augite and plagioclase and abundant interstitial brown glass. A quantitative analysis gave the following result:-

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

The rock appears to be a dark trachyte, with a large percentage of plagioclase, and, from the close resemblance that the analysis bears to that of the overlying rock, there can be no doubt that they both have a common origin. The geologi-

cal relations as mentioned above also point to the same conclusion.

At the top of the hill along the strike of the dyke another dark-coloured rock occurs of a far more basic character. The geological relations of this rock to the tridymite-trachyte are, however, exceedingly difficult to determine, as the whole surface of the hill near the outcrop is covered with grass.

The rock contains porphyritic crystals of plagioclase twinned on the albite law, generally with idiomorphic outlines. A few crystals of sanidine were also seen in section.

Augite is abundant, brown in colour, and displaying no dichroism. Polysynthetic twinning parallel to the orthopinacoid exists in the centre of some of the crystals, the more peripheral portions being untwinned. No olivine was observed in section. The ground-mass is glassy, with feldspar and augite microlites, and abundant grains of magnetite.

An analysis gave the following percentages:–

Both mineralogically and chemically this rock shows great resemblance to typical basalts, and should be classed with this species.

Sections were also made of the dyke that penetrates the rock at B. Feldspar of a plagioclastic variety is abundant, but no sanidine was observed. Augite is present in idiomorphic crystals of a brown colour, and is not dichroic. Apatite is particularly abundant, and grains of magnetite are of frequent occurrence.

The alkalies were not determined. The rock is undoubtedly one of the ordinary augite-andesites of the Lyttelton system, and bears no relation to the previously-mentioned rocks.

Another rock outcropping close to the tridymite-trachyte was also examined. Its geological relations could not be made out, as all the surrounding slopes are covered with grass.

Under the microscope numerous large porphyritic crystals of plagioclase can be seen, and a few of sanidine, but the two do not occur in contact.

No augite was seen, but a highly-dichroic mica with parallel extinction, probably belonging to the biotite series, was present in a few crystals.

The ground-mass consists of crowds of interlacing crystals showing parallel extinction, their length being many times as great as their width. Their polarisation colours are greys and bluish-greys, not so high as those of the feldspars. They would appear to be orthorhombic zeolites, though no fibrous aggregates have been detected.

Microscopically, the rock is of a greenish-grey colour, with shining lustre in places. The specific gravity is 2·65. A quantitative analysis resulted as follows:—

These percentages bear a certain resemblance to those in phonolites, the high percentage of alkalies and small percentage of lime being particularly characteristic. As, however, the rock is evidently considerably decomposed, and no specimens of the unaltered rock could be obtained, little reliance could be placed on the analysis.

On digestion in cold hydrochloric acid a large quantity of gelatinous silica separated out, a reaction eminently characteristic of phonolites. It is highly probable, however, that the gelatinous silica is in this instance a product of the decomposition of the zeolites.

Judging from its chemical composition, it would appear highly improbable that this rock has a common origin with the tridymite-trachyte. No other rocks were found in the neighbourhood of the tridymite-trachyte except a few small dykes 6in. to 18in. wide, and, as they obviously have no bearing upon the origin of the lava-flows, they were not submitted to a critical examination.

In considering this small subsidiary eruption of the Lyttelton system as a whole, it may be said that the order of the extrusion of the rocks is wholly in accordance with Durocher's law of succession of igneous rocks. First we have an intermediate lava represented by the black trachyte; next comes the tridymite-trachyte, as a representative of the acid group; and finally the basic rocks, as represented by the basalt.

welled from the shaft. This crater was quite extinct at the time of my first visit.

Having heard that explosions had taken place at Tongariro, and being unable to obtain information as to its extent or exact locality, I determined to visit the district again during the Christmas vacation to see what had actually taken place, and to note any facts that might appear worthy of being recorded. The road to the mountains is now in such fair order that it is possible to drive as far as Lake Rotoaira, which is situated between the volcanic cones of Tongariro and Pihanga. This plan of reaching the district was adopted, and on the last day of 1892 a small party pitched tents on the south shore of the lake, and made preparation for the ascent of Tongariro on the morrow. The evidence of an eruption was very clear from our camping-ground, and on portions of the road running along the side of the lake the deposition of débris and a peculiar sweet earthy odour that arose therefrom showed the location of the spot, and in some measure the character of the eruption that had taken place. I had purposed leading our party up the mountain by way of Kehetahi, but the demands of the old chief living at Otukou compelled me to forbear, and it was decided to attempt an ascent of the mountain byway of the rift, or gut, which had been made from Te Mari down the mountain-side leading into Lake Rotoaira. Bounding the northern end of the range between 4,000ft. and 5,000ft. is a belt of bush and scrub. The eruption had cut a deep channel through this bush, and up this it was arranged to climb.

Our party, six in number, two of them being my own children, started to make the ascent on New Year's morning. A day's rations for each, with one to spare for contingencies, was prepared, and at seven in the morning we were on the march in the direction of the gut on the mountain-side. We were not long in reaching this place, and we found to our great delight that the travelling was comparatively easy; so much so, in fact, that ladies could ascend the mountain by this track without much difficulty. The gut varies in width from 30ft. to 60ft., according to the depth of the sides, and it continues up the side of the mountain to a little beyond the limits of the bush, and within 500ft. of the crater of Te Mari. There it terminates in a great face of black basaltic rock, which is polished and smoothed and pitted, and has the appearance of an old waterfall, although at the time of our visit no water was flowing down the gut from the mountain. It was curious to note that all the exposed rocks in the waterway were finely polished, although they appear to have been exposed since the explosion on the mountain. The gut or channel had evidently been washed out by the water, sand, mud, and stones ejected from Te Mari, and which it seemed had not

only filled the channel, but had in places destroyed the trees which stand on the jagged banks. Most of the trees for a chain or so on either side of the channel had their leaves blackened, or reddened, or browned, as if they had been suddenly scalded by hot water, or the roots of the trees had been killed by hot water, the leaves remaining on the trees to brown and die. The material ejected from Te Mari on this side of the mountain was strongly impregnated with alum, and the water in the small water-holes at the base of every rocky face was very bitter and undrinkable, although as clear as crystal. The discoloration, and thereby the destruction, of the forest leaves in this way was to me of special interest in its suggestiveness, and I felt amply repaid for my trouble by the new light such an objective example threw upon a difficulty which had presented itself to me for some time in connection with the deposition of fossil leaves, &c. For several years I have occupied myself at intervals of leisure in collecting impressions of leaves, fishes, &c., from the Poverty Bay and Kidnapper Post-pliocene deposits. Some of the principal beds of the series are made up of a fine pumice, interbedded with a kind of pumice-mud, in which there are beautiful impressions of the forest flora—leaves, flowers, and ferns—of this country, mixed with impressions of fresh-water fishes (koura?) and other traces of animal life. From the appearances represented by the leaves on the scalded trees, I am of the opinion that this mode of destruction explains and illustrates the manner in which the leaves in the Poverty Bay and similar beds were destroyed and subsequently deposited, in a lake or estuary. The impressions on the pumice-mud are raised like the impress on a coin, and they show each vein and veinlet and all the surface irregularities such as appear on a green leaf. Such impressions, it seems to me, could only be made in the case of leaves whose growth had been suddenly stopped and destroyed without injuring the leaves. No doubt the reddened, browned, and blackened leaves from the dying or scalded trees on Tongariro will be carried into Lake Rotoaira, or, maybe, into Lake Taupo, and there deposited with the fine pumice-mud which is constantly flowing into these lakes from the numerous streams and springs in the vicinity of Tongariro.

Beyond the belt of bush and scrub there is little or no vegetation on the mountain. A few scattered plants were gathered, such as gentian, Sophora, Celmisia spectabilis, Angelica, Ranunculus, a sweet-scented Pimelea, a Claytonia, and a Hectorella.

On reaching the old crater which adjoins Te Mari, and to which reference has already been made, the extent of the eruption could be plainly seen. The mountain, extending

from the old crater through the two shafts at Te Mari and passing along the slope of the mountain in a kind of circular direction, was rent in twain by an enormous fissure. This fissure had broken away a portion of the top of the mountain towards the north-east, and it had taken a direction along the foot of the higher slopes of Tongariro, so that the outer wall of the old original Tongariro crater has become a portion of the inner wall of the active vents at Te Mari. This new crater also includes the old extinct crater already referred to, and which on the south-west was showing signs of activity, it having been fractured in this direction at the time of the explosion. In the vicinity of the old shafts everything was in a state of intense commotion. Vast quantities of poisonous gases were rising from the rift, and the whole area on the north side of the rift was a seething mass of sulphur. Our party endeavoured to get near the central part of the rift, but the fumaroles and rising gases were found to be too dangerous for a venture; and our only means of seeing the centre of greatest activity was to ascend to the top of Tongariro overlooking the rift, and from this vantage-ground view the scene. Although the wind was favourable the depth of the rift could not be seen. Now and again water and mud were observed on the north-east, but no traces of flame or fire were noticed. Form appearances near the rift it seemed that water, sand, and small stones were the only things ejected at the time of the eruption, and these all in the same direction, but the top of Tongariro Mountain seems to tell a different story. I had crossed this mountain several times previously, but no sign of pumice had been observed on its sides or top. Now, however, the mountain tells a different tale. Scattered thinly over the top, and in pieces varying in size from ordinary grit to small pebbles, is a deposit of pumice, and the question arises, From whence did it come? This pumice is sometimes heavier than the ordinary froth pumice, and has a somewhat duller appearance than that seen in the cliffs bordering Lake Taupo; but there is no doubt of the fact that it is pumice. I noticed with some care the extent of its distribution, and found no traces whatever in the direction of the Blue Lake, whilst the deposit increases towards Te Mari. The Red Crater, in the direction of Ngauruhoe, was unusually active on the western side, and it is certain that Ngauruhoe had sent out black smoke and great quantities of dust about the time of the outburst at Te Mari. This is not only stated to be the case by Mr. Chase, an intelligent half-caste of my acquaintance who resides near Wai-o-honu, but Mr. Blake, of Tokaanu, told me that the dust darkened the air for several hours during the day following the eruption. Te Mari showed no signs of pumice on the lower parts of the mountain; and the only explanation that appears

through three river-basins—viz., the Wainui, the Akiteo, and the Manawatu—the two former emptying their waters into the ocean on the East Coast to the south of Cape Turnagain, whilst the Manawatu discharges its waters into the ocean in the South Taranaki Bight, a few miles to the west of the Foxton Township. There is a great difference in the character of the country drained by these rivers. The Manawatu drains an area which is essentially Pliocene and Post-pliocene, whilst the country drained by the Akiteo and Wainui Rivers belongs either to the Older Tertiary or to the Younger Tertiary series. After quitting the Ruahine Mountains the Manawatu passes through a valley made up entirely of young deposits, except in the single instance of the Manawatu Gorge, below Woodville, which separates the Tararua from the Ruahine Mountains. The valley extends from the Ruahine to the Puketoi Ranges, and is important as being, as far as the gorge at least, the remains of an enormous rift or subsidence which has been filled from the products of streams derived in great part from the volcanic district which is now separated from the area known as Hawke's Bay district by the Ruahine Range, which was slowly rising as the rift took place, and was no doubt the primary cause of the rift.

The Ruahine rocks towards the south are made up mainly of sandstones, having a great similarity to the New Red Sandstone of England. When climbing to the trig, station known as Wharati, at the south end of the range, a short time ago, I noticed that the Maitai slates, which are exposed at Maharahara, and which thicken out further north ward, were but slightly exposed here. Large boulders of jasperoid quartz overlying conglomerates were met with about 1,200ft. above sea-level; and at the highest elevation where there are traces of settlement blue fossiliferous clays were exposed resting against the slates unconformably. I have seen them in a number of cases elsewhere. Beyond this point the sandstones appeared, and no other kind of rock was seen up to the trig. station, where every exposure shows the fine-grained compact sandstone. In the Ruahine, immediately opposite Dannevirke, the sandstone appears in connection with splintery or drossy slates, but the upper rocks are sandstone, with here and there traces of a compact conglomerate of the millstonegrit type. The same kind of grit appears in the Whakarara Mountains, between Hampden and Kereru, and it may be that the latter range was connected at one time with the Ruahine in the direction indicated by the grit stone. The whole of the valley between the Ruahine and the Puketoi Mountains is made up mainly of Post-tertiary deposits. They belong to what may best be described as the Kidnapper pumice and conglomerate series. These beds, which are very thick in places,

rest on the blue-clay marls, which were once overtopped by limestones.

Along the banks of the Manawatu River, which passes down the valley two miles or so to the eastward of Dannevirke, there are exposures of these blue Younger Tertiary beds similar to what are seen in the Tukituki, just above the crossing between the Ongaonga and Ashcott, and also at the Kidnappers, immediately above the limestones, at the place known as the Black Reef. In several places a little further to the eastward of the river the limestones are seen similar to those at Heretaunga and at Ashcott, between the Tukituki and Tukipo Rivers. This, it seems to me, is important, because it connects all the limestones on the western flank of the Cretaceo-tertiary rocks into one great and continuous whole. These limestones are met with as outliers in a number of places flanking the Ruahine Mountain between Woodville and Kereru. The Mangatoro Stream, near to what is known as Hamilton's Homestead, appears to separate the younger from the older blue-clay marls. The latter marls are similar to those exposed in the cliffs between Waikare and Wairoa, but the fossils are too fragile to make a satisfactory collection. Between the younger and older series of blue-clay marls a calcareous sandstone is met with in places, which passes sometimes into limestone of fairly compact texture.

The limestone is finely exposed in a scarp some six miles or so beyond the Mangatoro Stream, and, as there is no stone suitable for road-metal between this place and Weber, or, indeed, between here and Wimbledon, no doubt it will be largely used for road purposes in the near future. This limestone is similar to that found in the gorge of the Tukituki River, on the side towards Waipukurau, and the same fossils, T. angulare and O. ingens, are common to both. The limestone found in the Wanstead Gorge appears to belong to the same series, and as an impure sandy calcareous deposit it is seen to pass between the two clay-marls midway between Patangata and Tamumu, on the right bank of the Tukituki River. The hills, which are topped by the limestone scarp, form the dividing-range between the east coast and the Manawatu basin, and from this place there are no rocks younger than these, which are, in reality, the youngest of the Puketoi rocks exposed in this direction. Proceeding further towards the coast the blue clays, wherever exposed on the roadside, are somewhat indurated, but they seem to be acted upon by strains at right-angles to the pressure, and they break from the rock in sheets with a kind of conchoidal fracture. These rocks have a great tendency to move glacier-like into the valleys; and the whole country can be read in the peculiar appearance presented by the moving masses towards the streams,

which they sometimes dam back until a new channel has been cut.

At the stream known as Kereru, five miles or so from Weber, the rocks belonging to the upper greensands appear. These sands contain concretionary bands of impure limestone, which are fossiliferous, but exposure to the weather rapidly acts upon them, and they quickly decompose. The greensands are filled with black flakes resembling lamellar hornblende, but whether they are hornblende or not I cannot say. These greensands seem to me to belong to the same series which are so largely developed along the coast-hills between Porangahau and Wainui—Cook's Tooth being the central height—and are first met with on the top of the hills overlooking Porangahau on the Wallingford side. In neither of the latter places, however, have I observed a ferruginous limestone band, but, as traces of this greenstone extend to the hills overlooking the Roan Creek, a mile or so from the Weber Township, there can be but little doubt that they are the representative beds of the coast greensands, seeing that the Waipawa chalkmarls make their appearance in this creek. Between Roan Creek and the Akiteo Stream, where it crosses the road, the whole area is made up of chalk-marls. In some places these marls have a conchoidal fracture, but near their junction with the blue clay they weather into small cubical pieces, and the whole exposed surface has what may be termed cleavageplanes not unlike the splintery slates at the base of the Ruahine, except in the matter of hardness. The blue marls continue from the Akiteo Stream past Tea-tree Point, and thence onward to the top of the hill leading to the Wainui Stream. No fossils of any kind were observed, in these blue marls.

At the bottom of the hill leading to the Wainui Stream the black and brown oil-shales are well exposed. They have been used here for road purposes, as they are the hardest rocks in the district. These shales have a very wide distribution along the east coast of the Island. Their most northern locality is at Port Awanui, a few miles to the south of East Cape. There they are largely exposed in connection with the greensands and the blue-clay marls. The next place where they appear as surface-rocks is near the Waipaoa homestead, on the Waipaoa River, thirty-five miles to the north-west of Gisborne, in the vicinity of the once much-talked-of Poverty Bay oil-springs. They are next seen well exposed near- Baker's Brewery, at Waipawa, within half a mile of the town, and again on the top of the hills overlooking Porangahau. In each place named they are met with in connection with greensands and chalks marls. Southward from Porangahau no trace of the rocks is again met with until reaching the Wainui Stream, when they are exposed three times along the high banks in a distance of

the present water-level, and the other 330ft., clearly showing that formerly the lake was at a higher level. The Waikato leaves Lake Taupo at Tapuaeharuru, and flows in a north-east direction down a well-defined valley for nearly twenty miles.

An inspection of the map will show that the Waikato basin here is bounded to the westward by a mountain-chain whose highest peaks are 3,800ft. above the sea. They run nearly parallel with the western shores of Lake Taupo. There is a general persistent trend in the range in a direction N. 40° Ei. Lateral offshoots diverge, but the general axis of the main chain has a dominant direction nearly north-east. This chain is continued on to Whakamaru and Tikorangi, and becomes confluent with the Patetere plateau and the high wooded country to the westward of Rotorua, where it disappears or becomes coalescent with the disjointed hills, Ngongotaha, Okohiriki, &c., which lie directly to the west of Rohorua, and stand from 2,500ft. to 2,600ft. above the sea. Twenty miles to the east of this main range lies the valley through which the Waikato River flows from Taupo Lake to Waiotapu Valley. The Waiotapu was evidently a continuation of the valley above through which the Waikato River flows from Taupo. The two together form the oldest topographical feature of the country, and along their course on either side are to be seen evidences of immense denudation as they were widened and deepened. To the west of them, extending to the main range, the ground is left projecting into high ridges and prominent isolated hills with valleys filled with alluvium, this general trend being from the range into the Waikato and Waiotapu Valleys. I think it is more than probable that the Waikato at one time flowed through the Waiotapu Valley to the sea on the East Coast, and that the main range before referred to formed the watershed of its basin on the northwest side. But its channel was obstructed, probably by subterranean disturbance or the volcanic action in the Rotorua district; it quitted the original valley, and eroded for itself a new channel in nearly a due west direction, through a pass of the range between Whakamaru and Titiraupenge.

The topography of the country and the land-sculpture in the new river-valley bear out this view. The waters of the river were poured back into the valleys, which they occupied for a time in the form of a serpentine lake or lake-like river with many arms spreading in between the spurs of the ranges. Round Tuahu, Ngautuku, and the other hills between Ateamuri and Taupo, are seen the old lake-beds filled with alluvial deposits. In the valleys between the hills are immense beds of pumice and sand in horizontal layers, sometimes over 200ft. in depth. Through these the streams have worn their channels down to the bed-rock, disclosing stratified layers of

drift-pumice and light sands, enclosing the trunks of trees and carbonised wood. The worn shore-like sides which surrounded these pumice-beds, cliffs of tufaceous rock, often plainly water-worn, and the stratified horizontal layers of light drift pumice, leave but little doubt that a large area in this part of the Waikato basin was occupied by a lake through which the river flowed. In my opinion, deposits of light pumice sands such as are here found could only be laid down in still water.

The elevation of the outlet through the range was at first 300ft. above the present bed. A steep narrow channel was formed through the pass, the successive stages in the process of lowering being marked by horizontal terraces round the south end of the gorge and the lake - basins in the valleys above. These terraces are of immense proportions, ranging to 200ft. above the present river-bed. An excellent example of these terraces may be seen near Ateamuri Bridge, where the Rotorua-Taupo Road crosses the river. Below the gorge the river eroded a deep and narrow channel through the loose tufa country along the base of the wooded mountains of the King-country. Here one looks in vain for the characteristic features which mark an ancient valley. The country through which the river flows has the appearance of an old plateau, along the bases of the ridges and hills of which the water cuts its channel, and there is nothing to mark its course as an ancient feature of the landscape—no prolonged area of depression along the course of the river, and very little terrace formation.

Another remarkable deflection from its natural course would seem to have taken place in the Waikato at Hinuwera, fourteen miles above Cambridge. Here we have a broad, welldefined valley, bordered on either side by waterworn cliffs, from 30ft. to 40ft. in height, sloping down through Hinuwera in a north-easterly direction towards Matamata. It is confluent with the valley of the Waikato above. The trend and height of the river-terraces, the character of the alluvium, the waterworn cliffs, and the general topographical features of the land all point to the conclusion, I think, that this was its old natural valley, and that the Waikato once flowed down through it to the sea in the Hauraki Gulf. For the causes which brought about the change in the Waikato's course here we seek in vain amongst the topographical features of the land. There is nothing to show why its natural course was impeded, and why it is not now flowing down the Hinuwera Valley to the Hauraki Gulf, instead of taking the unnatural course it has through the ridges of the Maungatautari and Hinuwera Ranges.

Here, again, we have the same sequence of events recorded that took place at the Whakamaru. It would appear that the

waters of the river were ponded back into the valleys above, which they occupied in the form of a sinuous lake, extending upwards for over eight miles, and covering the Waipa Plains, which were evidently the bed of a lake. The topography of the country bears strong evidence of this. We find the remains of a deep alluvial deposit which filled the valleys running in between the spurs in level plains. Through these deposits the streams, in eroding this channel, exposed strata, horizontally laid, consisting of rhyolite sands, pumice, and detritus, including the trunks of trees. At Paeroa, where the Auckland Agricultural Company's homestead at Cranston is situated, this deposit has a depth of 130ft., as exposed by the washed-out gully of the Piarere Stream. It extends down the Hinuwera Valley, and almost disappears at Parakau, four miles from the present bed of the Waikato.

Reference to the map will show the elevation of the lake bed on the Waipa Plains to be 340ft. above sea-level. A terrace of about the same height fringes the valley of the Waititi Stream on the opposite side of the Waikato, and extends down the river-side to Piarere. It is a remarkable fact that the height of the old river-bed in the Hinuwera Valley is only 280ft. at Piarere, and the valley slopes gradually down towards Matamata. Were the contour and levels of the valley as we now find them there would be nothing to impound the water in the lake, the old Waipa lake-bed being 60ft. above the outlet in the Hinuwera Valley. I shall have occasion to refer to this question again in considering the causes which brought about the changes in the river's course.

The highest terrace in the Maungatautari Gorge has an elevation of 300ft. above the sea. Water-worn rocks appear on both sides of the river at that height, and between them on either side of the river are seven rows of terraces extending down to the present river-channel, which is cut deep and precipitous through the rhyolite rocks.

The broad plain in central Waikato, in which the towns of Cambridge, Hamilton, Ngaruawhia, &c., are situated, has an area of 500 square miles. All over the lower areas of this plain we find an alluvial deposit, varying in depth from 150ft. downwards. The character of this deposit is unmistakable—it is no doubt the alluvium of the Waikato River, and differs in no way from that at Waiotapu. Whakamaru, and Hinuwera. Pumice-drifts are not found to any extent in the beds of any of the other rivers which flow into the Waikato middle basin. How these deposits came to be laid down as we now find them is an interesting physiographical question. The surface-height of the land at Cambridge is 220ft. above the sea, at Hamilton it is 120ft., at Ngarato 125ft., and at Morrins-

ville 82ft.; whilst at the Taupiri Gorge the elevation is only 39ft. Yet we find that the Waikato carried its alluvium to the Rotorangi Swamps, eight miles in a southerly direction, against the present grade of the country, the natural fall being north and east, towards Morrinsville and Taupiri, at the rate of 7ft. to the mile. It becomes at once evident, on considering the relative heights of the land in the middle basin, that it never could have been occupied by a lake, nor could these deposits have been laid by the Waikato at all if the levels of the country were as we now find them. The lake would have four outlets: one at Morrinsville, one at Hapuakohe, one at Matahura, and the present river-bed through the Taupiri Gorge (supposing it to have existed at that time), all considerably below the bed of the lake. It may be suggested that the deposits are estuarine, and were laid when the middle basin was a bay of the sea. The whole topography of the country and the character of the alluvium are against this theory. There is no trace of marine deposits to be found, and if any existed they would easily be discovered amongst the detritus which is scored and exposed by the streams, frequently to great depths, all over the plain. Neither is there any trace of a sea-beach found fringing the swamps round the clay-hills in the plain which were islands dotting the lake. Hochstetter says of the Middle Waikato basin: “The whole basin was, previous to the last elevation of the North Island, a bay of the sea, extending from the Hauraki Gulf far into the interior. The steep margins of the surrounding hills continue to this day displaying the seashore of old, and the singular terrace formation on the declivities of the hills and the river-banks within the basin is the result of a slow and periodical upheaving.” This being so, as the land gradually rose and the sea receded, tidal channels would have been left within the estuary, through which the rivers and streams would continue to flow out of the basin to the sea in the Hauraki Gulf—that is, if no change of the surface took place to prevent the natural course. We now find, however, that the valleys where these estuarine channels might be looked for are filled with an alluvial deposit of the detritus of the volcanic country brought down by the Waikato River, and placed in stratified horizontal beds, as they could only be laid in very slowly-moving or impounded water.

The depth of these deposits varies considerably. In the Rukuhia Swamp, between Hamilton and Ohaupo, they are from 50ft. to 70ft.; in the Piako Swamp, from 40ft. to 60ft.; at Hamilton, from 40ft. to 70ft.; and in the neighbourhood of Taupiri, the lowest point in the basin, it is a remarkable fact that the deposit is lightest. Beneath the deposit in many parts of the basin the old land-surface may be seen.

In the bed of the Waikato River at Hamilton several mairetrees appear standing as they grew, the present land-surface being 70ft. above them. In many of the gullies eroded by the streams trunks of trees are found lying horizontally, and some standing, their roots penetrating the old land-surface. The most interesting example of this character, because of the most recent occurrence, is that shown on Mr. E. B. Walker's property at Mona Vale, near Cambridge. A drain was cut about a mile in length through a spur of dry land to drain the Mona Vale Swamp into a gully which led to the Waikato River. During a heavy rainfall some years ago a scour started in this drain, which soon eroded a gully 70ft. in depth and several chains wide. At the bottom of this gully the ancient surface, consisting of a brown marly-looking soil, is exposed to view. The trunks of trees are seen lying on the old landsurface, and some are standing, their roots penetrating the old soil where they grew.

The Waikato flows in almost a direct course from Cambridge to Ngaruawahia in a north-westerly direction, crossing, the former estuary diagonally. In a flat alluvial valley like this we should naturally expect to find a winding river and a broad and terraced river-valley, instead of which there is a comparatively narrow valley, a deep-cut channel, and the river runs in a direct course, until it is stopped by the Hakarimata Ranges, near Ngaruawahia; it then follows the base of the mountains to the Taupiri Gorge.

Five miles and a half east of the Waikato River, below Huntly, there is a wide valley extending from the Manga-whara Stream, in the middle basin, to the Matahura, in the lower. It is very evident from the topography of the country that this was at one time the outlet for the middle basin, and the Waikato flowed through it and down the Matahura Valley, through Waikare Lake and the Whangamarino Flats. That the Taupiri Gorge, through which the river now flows, was formed subsequently I think there can be very little doubt. Captain Hutton, in his paper “On the Alluvial Deposits of the Lower Waikato, and the Formation of Islands by the River,” says: “There appears, therefore, to be no geological evidence of the sea having been in the Lower Waikato Valley since the upheaval of the Waitemata series—that is, since it has had any existence. I therefore think that the fact of the presence of several littoral plants in the Lower Waikato basin, brought forward last year by Mr. Kirk, may be best explained by supposing that they have spread down the river from the Middle Waikato basin, after the formation of the Taupiri Gorge.”^* The evidence of changes in

the level of the land, and alterations in the courses of the river in the Lower Waikato basin, are numerous and interesting from the surface-geologist's point of view, and a great deal might be written about them, but it is not my intention to enter fully into a description of this basin at present. One of the most interesting features of the Lower Waikato basin is the Matahura-Whangamarino Valley, which lies to the westward of the wooded Hapuakohe Ranges. The Matahura and Whangamarino Rivers rise in the centre of it, the former flowing to the south and the latter to the north-west. Their sources are a very short distance apart, and are separated by a low saddle. This has evidently been the valley of a large river at some period, and does not owe its erosion to the small streams which now occupy it. There are evidences of vast erosion high up on the sides of the valley, the remains of ancient river-terraces now worn and wasted by the elements. This was probably the course of the Waipa River when the Waikato flowed into the sea in the Hauraki Gulf. The alluvium of the valley is quite different from that of the Waikato; it is an argillaceous deposit, free from pumice or the rhyolite sands which characterize the deposits of the Waikato. It is very fertile. The lands in the Matahura and Waerenga Valleys derive their rich qualities from it, the latter being some of the most fertile in the Waikato district. It is the same alluvium which characterizes the rich lower terraces of the Waipa River, from Ngaruawahia up into the limestone land in the King-country, and is traceable along the Mangawhara River into the Matahura Valley.

Passing now from the Waikato to the Piako basin, we find again evidences of changes, as shown by the raised beaches, ancient terraces, and the river-alluvium. The level, swampy plain extending from the Hauraki Gulf to Te Aroha is plainly a combination of the bed of the gulf: the base of the hills on the western side of the valley shows distinctly the remains of the former coast-line. At Maukoro, twenty miles inland from the sea, close to the western bank of the Piako, and near the confluence of the Waitoa and Piako Rivers, an old raised beach, standing about 17ft. above high-water mark, is to be seen. There is a consolidated slag or marl deposit containing shells and unmistakable crab-holes, such as we see on the soft beaches at present. Along the banks of the Piako there are numerous sand-banks and banks of sea-shells, clearly showing that at no very remote time the Lower Piako Valley was a shallow bay of the sea. The immense quantity of pumice and other detritus from the volcanic districts laid down as river-alluvium in this large valley shows that it was the valley of a great river flowing through a volcanic country; and I have no doubt but the Waikato brought down the alluvium seen in the

upper portions of the plain, by Matamata. The alluvial beds of the lower areas of the Piako basin from the confluence of the Waitoa and Piako to the sea differ in a very remarkable manner from those higher up, and in the Waikato basins. Here we find a heavy argillaceous deposit similar to that of the Waipa River. A large area on the western side, and between the Piako and Thames Rivers, is covered with it. The land is extremely fertile, and if it could be drained would be some of the best soil in the country. The source from which the alluvium came is an interesting question. That it should be found in the lower area of the valley, whilst higher up, on the plains of Piako, Te Aroha, and Matamata, the alluvial deposits are of pumice and sands similar to those in the Waikato basins, is not easy to explain. The tributaries of the Piako may have brought down clay-alluvium from the Maungakawa Ranges, but it would necessarily be limited in quantity, from the small area of the ranges which they drain. I think it best explained by supposing it to have been brought down by the Waipa River from the limestone land in the King-country previously to the great upheaving and changes in the Waikato basins, and laid down in the lower part of the Piako Valley as an estuarine deposit when the Hauraki Gulf extended further inland. There is some evidence to favour this supposition. The Mangawhara Stream rises near Hoeatainui, within three miles of the Piako River at its confluence with the Waitoa. A low saddle in the fern-ridge which separates the head waters of the Mangawhara from the Piako Valley would seem to have been eroded by a river. Terraces are traceable on either side of the saddle. At Hoeatainui, and all along the Mangawhara Valley to the junction of the river with the Waikato at Taupiri, the alluvium is of similar character to that of the Lower Piako Valley. It seems probable, therefore, that at one time the Waipa occupied the Mangawhara Valley, and flowed into the Hauraki Gulf at Maukoro.

From the foregoing observations it would appear that the Waikato River for a long period of its history has undergone successive changes in its course At each change it would appear to have left its natural valley, and, turning to the westward, found a new course through the ranges which separate one valley from the others. Each basin would appear to have had extensive lakes situated within it. The present topographical features of the country do not afford sufficient evidence of the causes which effected these changes. If the levels of the country were as we find them to-day there would be nothing to impede the Waikato River in its old and natural course by the Hinuwera Valley to the Hauraki Gulf. And the contour of the Middle Waikato basin would not permit of the existence of the lake: neither would the Waikato River

occupy its present course directly across the plain, cutting through a series of clay-ridges, whilst the fall of the country from Cambridge is in a northerly direction. To subterranean movements altering the surface-elevation of the land it is evident these changes in the river's course are due; and these movements of elevation of the surface were of a paroxysmal character, or, at least, too rapid to allow the river to erode its channel deeper as the land rose. The evidences of elevation and depression we have are numerous. Captain Hutton proves submergence at the Thames by finding at a depth of 30ft. below sea-level, near Shortland, kauri-gum, raupo, and pieces of wood. He continues as follows: “It would thus appear that when the alluvium full of boulders found on top of the hills (near Shortland) was forming, the land was 1,000ft. lower than at present; that it then gradually rose until it was 100ft. higher than now; and at that time the Thames ran farther north than Shortland. The land then sank to about 10ft. or 12ft. lower than now, and subsequently has again risen to its present level.” I would here remark that when the land at Hauraki was 1,000ft. lower than at present—assuming that the movements of elevation and depression were unequal in the different parts of the district (a supposition of which we have some proofs, as shall be shown later on)—the Waikato River would flow down the Hinuwera Valley to the Hauraki Gulf, which would at that time extend far up the valley. As the land rose until it was “100ft. higher than now,” probably the axis of elevation would be along the main range from Cape Colville to Rotorua, with a contemporaneous subsidence to the south-west. The changes of level may be supposed to have ponded back the Waikato River into its valley above Hinuwera until it had graded a new channel through a pass in the Maungatautari Gorge. And the same explanation may be applied to the phenomena in the Middle Waikato basin. When the land in the Hauraki was “1,000ft. lower than now” the Middle Waikato basin was probably a shallow bay of the sea. As the land rose along the main range until it was 100ft. higher than now, the waters of the Waikato were impounded in the middle basin, covering all the lower areas of the valley as a shallow lake, which were then filled with the alluvial deposits we find there now. The formation of the Taupiri Gorge would probably have taken place at this period. The direct course of the Waikato River from Cambridge to Ngaruawahia, and the absence of a wide valley, may be taken as indicating the rapid formation of the riverbed, which was probably the result of the changes of level. Mr. James Stewart, in his paper on “Evidences of Recent Changes of Level in the Waikato District,” gives the following: “The proofs of subsidence we at present adduce are

crystal seems composed of a kernel round which new material has been deposited (Pl. XLIX., fig. 2, and Pl. XLIXa., fig. 3). In some cases this may be true zonal structure, but sometimes the wave of extinction passes outwards gradually, so that there are no zones at all. The kernel is at times rounded in form, and seemingly corroded, but the resultant shape is idiomorphic. In one case the gradual approximation to the crystallographic outlines could be traced. This structure is not peculiar to the feldspar, but belongs to the augite in a small degree, and appears faintly even in the olivine. There are several facts which show that this has been produced late in the history of the crystal:—

(1.) The kernel is usually irregular in shape, as if it had suffered injury from various solvents, &c.

(2.) The alteration products and inclusions are usually confined to the core, while the periphery is usually free.

(3.) Cracks in the core suddenly terminate at its edge; of course, many instances occur in which they are prolonged through the surrounding portion.

(4.) There is often a zone of alteration products at the edge of the core, as if the crystal had been weathered there and had commenced growing afterwards.

(5.) Twin lamellæ terminate at the edge of the core, though a few sections showed them prolonged further.

(6.) The periphery is often twinned in a different direction from the interior.

These observations seem to show conclusively that the crystals had suffered weathering before they were added to. If this is the case the rock must have been solid at the time, and the question is, Where has the new material come from? If the crystal had been enlarged while the rock was molten it would be easy to understand, but the appearance of weathering renders such an hypothesis improbable. This has been noticed before by Professor Judd (Vide “Quarterly Journal of the Geological Society,” vol. xlv., page 175), but in that case the crystals which showed growth were in a glass, and he supposes they grew at its expense under altered conditions of temperature and pressure. It would be difficult, however, in this case to account for new growth in this way, since the ground-mass is holocrystalline, and shows no alteration in the neighbourhood of the anomalous crystals. These rocks, being from near the surface of a Tertiary volcano, cannot have been buried under subsequent lava-flows, or under sedimentary deposits, so the growing of the crystals cannot have been caused by the influence of changed conditions of temperature and pressure on a glassy ground-mass. Nor can the crystals have been added to by water saturated with feldspathic minerals, forming accretions round minerals re-

sembling the matter in solution, since the temperature and pressure required for this would not be such as would occur in a dyke which reached the surface. We can hardly suppose that the dyke suffered alteration while it was cooling, owing to the presence of imprisoned hot water, but, if it were the case, then it would explain all the facts. The water saturated with mineral matter would have both a disintegrating and a restoring effect. It would account for the presence of alteration products, and the deposition round a corroded crystal would proceed as the water cooled. There would be no sensible alteration in the ground-mass, though some of the material might be drawn from it. It is usually the case that the ground-mass is more acidic than the porphyritic mineral, and so the new outside layers ought to be more in accordance with this than the kernel. The fact that the twinning extends faintly into the periphery would not be contrary to this hypothesis, as there is evidence that twinning is a structure impressed on minerals as they cool. This is perhaps a hazardous suggestion, but the case seems difficult to explain. It may be that these anomalous crystals were part of an old lava-flow which had suffered weathering near the surface, and then been buried under subsequent flows; and that, as the dyke penetrated it, parts of it had been caught up and the crystals afforded nuclei for crystallization, just as a piece of alum put into a solution of an alum begins to crystallize afresh. All the phenomena observed would be explained by this; but it is rather hard to conceive that the occurrence should be so general throughout the dyke if produced by this means alone.

Augite.—Augite crystals occur abundantly as rounded grains, but occasionally in lath-shaped forms up to ¼in. in length. They are of a brownish colour in ordinary light, but at times they have a purplish tinge, and in these cases there is very faint pleochroism. They contain inclusions of magnetite, which are usually absent from the periphery. Their characteristic features are the zonal structure, which has been dealt with before, and a remarkably perfect cleavage. In some cases it approaches the perfection of that of diallage. In the sections which show this there is only one set of cleavage-planes, but in those which show two sets it is not so perfect by any means, and becomes mere irregular cracks. The sections which show one set of parallel cleavage-cracks will be parallel to the axis of c. In estimating the extinction-angles with these the maximum result recorded was 44°. The crystals which showed this were usually lath-shaped. Those which showed two sets were short and idiomorphic. In one of these latter the extinction was symmetrical to the cleavage-cracks, and also parallel to a twin lamella running through

2,600 fathoms. Owing to an insufficient number of soundings, the contour of the plateau has not been determined, but it is supposed to extend as far eastward as the Chatham Islands; while to the westward, especially in the south-west, the line of the plateau is almost identical with the coast-line. The coast-line itself also bears evidence of subsidence. Those who have travelled only from here to Wellington have probably noticed how the curve of the hills reaches almost to the water's edge. This shows that the land has had a downward movement in recent geological times. If the land had been stationary we should have had high cliffs, caused by the erosive action of the sea, presenting themselves; or, if the land had been rising, extensive sea-beaches would have fringed the coast. Small islands, near the coast, like Pepin Island, D'Urville Island, Arapawa Island, and Kapiti Island, also bear evidence of the subsidence of the land. These islands are but the tops of hills which once formed part of the mainland. A glance at the map of New Zealand also leads us to conclude that New Zealand had once a more extensive land-area. The coast-line, as you will see, is characterized by a few bold headlands with extensive bights lying between. These headlands are composed of hard rock which has been better able to resist the action of the sea, while the places into which the sea now flows, forming extensive bights, once formed part of the dry land. The remarks about the islands in Cook Strait will also apply to the Barrier Islands, White Island, and Stewart Island.

Let us suppose, then, that the submerged plateau of which we have spoken was once high above the water; that the contour of that plateau was the boundary of an extensive continent which extended from East Cape in the North Island to Shag Point in the South Island: then the place which we now call Cook Strait—I mean the narrow part—was merely a pass in the mountain-chain; and the place which we now know as Tasman Bay was a broad valley, through which, probably flowed a large river, the upper reaches of which are represented by the streams which at present drain into the bay.

The greatest depth of Tasman Bay does not exceed 50 fathoms, while a great part of it has a depth of less than 50ft. When the submerged plateau, then, stood above the sea some hundreds, or probably thousands, of feet, Tasman Bay was not merely a valley, but an elevated one; and the mountains by which we are surrounded, having a much greater altitude, were covered with perpetual snow, and glaciers filled our now smiling valleys. This fact is borne out by the extensive glacial deposits found in the Nelson District. The Moutere Hills, and part of the Port Hills, are of glacial origin.

The moraines of glaciers are also found in the neighbourhood of Lake Rotoiti, and in the Takaka district.

While we have good reasons for believing that the surrounding district was once much more elevated than it is at present, we have abundant evidence to prove that it was once far below the level of the sea. Beneath the glacial deposit to which reference has already been made there lies a series of stratified rocks, which, by their lithological character, and by the fossils which they contain, give unmistakable proof of a deep-sea origin. These rocks consist of sandstones and clays, and many of the fossils found embedded therein are those of species now extinct. Some of the lower members of this series are well developed in the Port Hills. When walking round the rocks one is obliged to tread on the upturned edges of the lower members of this series, known as the Lower Miocene formation; while in the cliffs above, especially near the basin, the rocks may be seen dipping into the hill at an angle of about 50°. These rocks, when formed, must have been laid down in a horizontal position; hence their present upturned condition must have been brought about by a considerable amount of upheaval in the earth's crust. Numerous fossils may be found in the above-mentioned rocks, but owing to decomposition it is very difficult to get perfect specimens. A few good ones were found in the tunnel driven by Mr. Brown in his search for coal.

Passing from the Port Hills to Richmond another set of rocks is met with, known as the Wairoa series. These rocks extend from the hills about Richmond to the Wairoa Gorge. They belong to what is known as the Triassic formation, and are older than the Miocene deposits of the Port Hills. Their relation to the rocks of the Port Hills is shown on the sketch, where the rocks of the Wairoa series are seen to dip below those of the Port Hills, while the Port Hills series forms what is known to geologists as a synclinal arrangement. The Wairoa formation is exceedingly rich in fossil remains, some of the hills above the gorge being literally masses of fossils. They may be found in the bed of the river just before entering the gorge, and on the hill-slopes this side of the river, as far north as Richmond. It is the study of these fossils that has led to the determination of the age of the rocks in which they are embedded. Monotis salinaria and Mytilus problematicus are the most common. Mention is made in the “Outline of New Zealand Geology” of teeth having labyrinthodont characters having been found in this formation. This being so, we may well suppose that, while these rocks were being deposited in the shallow seas of that age, amphibious creatures of considerable size disported in the lagoons, or basked upon the mud-flats.

Leaving Wairoa Gorge, and travelling up Aniseed Valley, a still older series of rocks is met with. These rocks are known as the Maitai slates, and form part of a very extensive system, known to geologists as the Carboniferous system. These slates, in the lower part of the valley, consist of fine-grained clay-slates. Further up the valley the slates become calcareous; and finally a magnificent belt of mountain limestone is reached. This limestone, and the slates already mentioned, are the principal rocks of the Carboniferous system. These rocks are very extensive, and form the greater part of the mountain-chains of the district. They pass from end to end of the provincial district, forming part of the Spenser Mountains, St. Arnaud Mountains, and the low mountain-range running from the St. Arnaud to the Pelorus Sound. As offshoots from the main range they reach almost to the Town of Nelson—Fringe Hill and Botanical Hill being composed of this rock. Extending from Mount Franklyn to D'Urville Island, and running in the same direction as the mountain limestone and the Maitai slates, is a stretch of country known as the “mineral belt.” This formation presents a marked contrast to the limestone and slates of the Carboniferous formation. The latter are covered with dense bush, having a luxuriant undergrowth, but, when the mineral ground is reached, the bush terminates abruptly, and gives place to a succession of bare hills, whose rugged grandeur cannot fail to impress the least observant. The lithological character of the rocks is also strikingly different. Instead of regularly-stratified rocks, such as are found in the Port Hills, the Wairoa series, and the Maitai series, we have masses of dark horn-blendic rocks, diorite, serpentine, and dunite. Dunite, the typical rock of the Dun Mountain, is an olivine rock containing traces of chromium. The rock itself is crystalline, and of a yellowish-green colour; but where exposed to the weather its hue has changed to a rusty-brown; hence its appropriate name, dunite. It is this formation that contains the deposits of copper and chrome to which I shall refer more fully when dealing with the economic minerals of the district.

Reference has already been made to the mountain-forming character of the Maitai slates and the underlying Carboniferous limestone. I shall now attempt to describe how these rocks were formed, and how they came into their present position. Limestone, as most of you are aware, is of organic origin. Carbonate of lime exists in solution in sea-water. Certain marine animals have the power of extracting the carbonate of lime from the sea-water and of converting it into a solid substance, which they use as a protection or covering for their, bodies. When these animals die the shells in which they

lived are left behind, and by repeated accumulations of such shells vast deposits of calcareous rock are formed. All our great masses of limestone have been formed in this way, the coral polypi having had the greatest share in their formation. Try for a short time, then, to blot New Zealand as it is out of your memory, and conceive instead a coral reef in a tropical sea—something like the Great Barrier Reef off the coast of Australia. The sea-bottom is slowly sinking, but fresh layers of coral are formed, till several hundreds of feet have been produced. Then, owing to rapid subsidence or change of climate (or, perhaps, both), the work of coral-forming ceases, and layer upon layer of fine mud is deposited on the top of the coral-reef, till a thickness of several hundreds of feet of fine silt has been formed. This silt, of course, must have come into the ocean from the rivers of some adjacent land-area, and represents so much waste from that land. While this silt was being deposited the superincumbent pressure of its own weight, added to the weight of the ocean above, would consolidate it into a hard rock, and produce what is known as a clay-slate. Then an upward movement commences in the earth's crust beneath these rocks, and they are gradually raised till they stand thousands of feet above the level of the sea—not as we know them now, presenting an innumerable variety of landscape, made of valleys, and mountain-ridges, and mountain-peaks, but as a broad belt of elevated land. After a mountain-chain had been thus formed—or, probably, during the latter period of its formation—the pressure from beneath was so great that the overlying crust of limestone and slate gave way, and rock-matter, in a more or less plastic state, from the interior of the earth, was forced into the gap, thus giving rise to the mineral belt, which, as I have already stated, is composed almost entirely of crystalline rocks.

After the formation of the mountain-chain as a broad belt of elevated land, the work of denudation went steadily forward. The heat of the sun by day, the cold of frosts by night, the storms of rain, and the never-ceasing chemical action of the atmosphere began to soften and wear away the rocks. The rain-water, in its endeavour to reach the sea, would form watercourses, which, by the erosive action of the water, would deepen and widen their channels till rivers were formed. The rivers, especially in time of flood, aided by innumerable fragments of rock loosened from the parent rock in the manner already described, would continue to wear down the country, thus forming the broad and deep valleys so characteristic of the hilly parts of this district. When looking down into any of these valleys from some elevated spot, and remembering at the same time that the whole of the valley has been scooped

out of the solid rock by the action of the river, two forcible questions present themselves to the mind: First, what has become of the material which once filled the valley from crest to crest of the existing hills? Second, how long did it take the river to remove that enormous mass of matter? The answer to the first question is comparatively easy. The matter thus eroded has been carried down to the sea, the lighter particles floating far out into deep water, and these settling down to form fresh deposits of sedimentary rock, while the heavier portion would settle at the mouth of the river, and there form a delta. Beneath our feet at the present moment lies the débris of the rocks which once formed an integral part of the mountains near us. The greater part of the Town of Nelson stands upon the delta of the Maitai, while the delta is still extending seaward by fresh accumulations brought down by every flood. In the same way the Waimea Plain has been reclaimed from the sea by materials brought down from the hills by the Rivers Wairoa and Wai-iti. The second question, “How long did it take the river to erode the valley?” cannot be answered definitely, but an approximation may be made. By calculating the amount of sediment held in suspension by several rivers, and by taking into account the rate at which they flow, it has been found that a river lowers the area of its basin about 1ft. in two thousand years. Not knowing the mean depth of our river-basins, I am unable to make any estimate upon this basis; but by making the most liberal allowances, in a rough guess, at least hundreds of thousands of years would be required for the formation of many of our valleys.

Thus far I have dealt almost exclusively with the geology of our own immediate neighbourhood. The fear of making this paper too long prevents me this evening from touching, even in barest outline, on the interesting geological facts connected with the Owen, the Wangapeka, the Baton, the Takaka, and the Collingwood districts. I shall therefore close this paper by a brief reference to the minerals of economic value found in the provincial district, mentioning, as I pass, the geological formations to which they belong. First in importance are the coal-deposits. The coal-deposits of New Zealand belong to the Cretaceo-tertiary formation. In this respect New Zealand differs widely from other countries, where coal is usually associated with rocks of Carboniferous age. The Cretaceo-tertiary formation comes between the Miocene rocks of the Port Hills and the Triassic rocks of the Wairoa Gorge. Its principal areas of development may be seen by a glance at the map, where the parts coloured green indicate the presence of Cretaceo-tertiary rocks. These coal-deposits must in the future prove a source of great wealth to the district.

The Buller Coalfield alone is estimated to contain 140,000,000 tons of good bituminous coal; the West Wanganui Coalfield, 25,000,000 tons of pitch-coal and 12,000,000 tons of brown coal; while the Brunner Mine contains about 4,000,000 tons. To the sum of these must be added the coal contained in the Collingwood Coalfield, which has an area of about twenty square miles. The output of coal for the Nelson District is about 200,000 tons per annum.

Gold, the next mineral of importance, is found in many parts of the Nelson District, Collingwood and the West Coast having so far yielded the largest quantities. The gold in the Nelson District is usually found in the gravels and drifts which have been derived from the older metamorphic rocks. These rocks stratigraphically underlie the Maitai formation, and are coloured sepia on the map. The gravels and drifts in which the gold is usually found are coloured red or yellow, red representing the older gravels, and yellow the more recent formations. On the map only the larger deposits of these formations have been represented. There are innumerable patches of recent gravels found in almost every river-valley of the district, which could not possibly be represented on a map of so small a scale. It must be borne in mind, however, that only the gravels from the older formations are auriferous. The Maitai slates, for example, as far as is known at present, are not gold-bearing; consequently, the gravels derived from them are not auriferous. The gold exported from the Nelson District last year was valued at £16,000, while since 1857 to the present time six million pounds' worth of gold has been obtained from the Collingwood district alone. Copper and chrome are found in many parts of the Dun Mountain mineral belt, but owing probably to the want of scientific prospecting these minerals have not yet been discovered in sufficient quantities to pay for working.

Argentiferous galena—that is, silver-bearing lead-ore—has been discovered at the Owen and at Wangapeka; and at Collingwood silver, lead, zinc, nickel, antimony, copper, bismuth, and iron are known to exist, in addition to the gold already referred to. Plumbago is also found in the Collingwood district, but not sufficiently pure for commercial purposes. The iron in the Collingwood district belongs to the class of ore known as limonite, or brown hæmatite. This substance is at present made into paint; but probably the time is not very far distant when iron will be smelted from these valuable deposits of ore. At the Hope Saddle an interesting iron compound is found; it is known as vivianite. It is an iron-phosphate, and is of a bluish colour. A specimen of it will be found upon the table, together with specimens of all the rocks and minerals mentioned in this paper.