COAL DEPOSITS OF NEW ZEALAND
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COAL DEPOSITS OF NEW ZEALAND:
THEIR NATURE AND CLASSIFICATION.
IN New Zealand no coal seams have yet been discovered that can be referred to Paleozoic coal measures, such as occur in the Northern Hemisphere, as all the formations which contain workable seams belong to the Secondary or Mesozoic, and to the Tertiary or Cainozoic epochs.
The quality of the coal found in New Zealand is, at the same time, extremely varied, some of it being for all practical purposes equal, if not superior, to much of the coal used in other parts of the world, while on the other hand, a great deal is of a comparatively inferior description, though it still has a great local value as fuel in the districts where it occurs.
At first it was attempted to class these various qualities of coal according to their respective geological ages, but though this may be effected when the geology of the country is better understood in detail, the evidence on which we must rely for such a classification is as yet contradictory. It has, therefore, been considered more advisable in the present state of our knowledge to adopt a provisional classification founded on the chemical composition of the coals.
The amount of water chemically combined with the coal being not only the best theoretical indication of its value, especially if the proportion of inorganic matter or ash be deducted in making the calculation, but also the most important point in considering its practical value as fuel, it is proposed to divide the coals found in New Zealand into two groups, under the terms Hydrous and Anhydrous coal, or, those which still contain a large percentage of water chemically combined with them, and those which we may assume to have been deprived of that water by a chemical change, which, in some cases, may have been induced by causes operating feebly throughout lengthened periods, or, in others, has been rapidly effected on more modern deposits of carbon, under circumstances which favoured a more energetic action.
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In the following table an abstract is given of the average results of about seventy chemical analyses which have been made in the Laboratory of the Geological Survey, by which the respective characters of each group of New Zealand coals can be compared with that of Australian and English coals.
ABSTRACT showing AVERAGE COMPOSITION of the COAL of New Zealand, as compared with Australian and English Coal; from analyses made in the Laboratory of the N.Z. Geological Survey.
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These in quality correspond with the Brown Coals so extensively mined on the continent of Europe, and, fortunately for many of the districts of New Zealand, where firewood is deficient, they are very largely distributed throughout both Islands.
A point worthy of remark is, that whereas in Europe the deposits of Brown Coal (or Lignite as it is usually termed) occur generally in local beds of immense thickness, but confined to limited areas, those of New Zealand form regular seams of moderate thickness, and associated with alternating beds of clay, shale, and sandstone, somewhat as with the older coal formations.
The Brown Coal formation of New Zealand is, moreover, frequently involved in dislocations and disturbances of the underlying rocks, a circumstance which has no doubt given rise to a great variety in the value of the coal seams as fuel.
As a rule the Hydrous coal measures lie on the eastern slopes of the axial rocks in both Islands, whereas the Anhydrous coal fields are found either west of lines of dislocation, or having a prevailing westerly dip.
This apparent coincidence, which may prove of great practical use in tracing these deposits, requires further investigation however before we assume that the position of the coal, relative to the line of dislocation, has any necessary bearing on its quality.
The Hydrous coal is of a brown colour, but hard and glossy, and frequently contains a quantity of fossil resin, which greatly facilitates its combustion.
Its principal defect is its bulk in proportion to its weight, and its tendency to crack and break into small fragments by desiccation on exposure to the atmosphere, although in this manner it loses only a small proportion of the total quantity of the water which enters into its composition, and which gives to it the character of Hydrous coal.
The remainder of the water, usually from 12 to 20 per cent., can only be expelled by raising the temperature very considerably, and much of the heat derived from the combustion of the coal is thus absorbed.
Nevertheless, it is a most valuable fuel, and is largely used both for domestic purposes and for raising steam.
It is also highly applicable to the manufacture of bricks and pottery, and for other economic purposes.
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The best known deposits of this coal in the North Island are those mined at Drury, twenty miles to the south of the City of Auckland, and at various points in the extensive and fertile valley of the Waikato River, where they will have a great local value in connection with the facilities for internal steam navigation which that river affords.
Seams of this coal, varying from six to fifteen feet in thickness, occur at intervals over a large area of country, so as to lead to the conclusion that the formation is very extensive.
Prom the existence of seams of this coal on the Mokau River, north of Taranaki, and on most of the tributaries of the Wanganui River, it is probable that another extensive Brown Coal field exists in this portion of the Island, while there are also indications of a third extension of this same formation on the East Coast.
Our geological knowledge of these districts is as yet too limited to allow of an approximate estimate being made of the extent and total thickness of these Hydrous Brown Coal deposits in the North Island; but there can be no doubt that they underlie an area of at least several hundred square miles in extent.
In the South Island, the best known and most important deposit of the Hydrous Brown Coal formation is that on the south-east Coast, northward from the Molyneux River, where it extends continuously over at least forty-five square miles, forming hills 500 to 1000 feet in height, broken into sharp ridges by the outcropping beds of grit and conglomerate. In this formation there are several seams of good coal varying from six to twenty feet in thickness, their aggregate thickness in a section three miles in length, exposed on the sea-shore, amounting to 56 feet.
The total quantity of coal in this district has been estimated at 100,000,000 tons. Two large mines have been opened in this coal field.
The Clutha Mine is on the sea coast, about three miles from the mouth of the Clutha River, and three quarters of a mile from a bend of the river where vessels can lie alongside a wharf and load in safety at all times, and to which point the coal is brought by an iron tramway.
It is, however, impossible to effect a regular shipment of coal from this place to the market, owing to the risks encountered at the entrance to the river, where the navigation is exceedingly difficult.
The principal consumption of this coal has therefore been for
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local use, and for the steam navigation of the river; but as it is proposed to construct a railway from Dunedin to the Clutha Valley, a distance of sixty miles, this valuable fuel will be brought into more general use than at present.
The only other mine of importance opened in this coal field is in the vicinity of Tokomairiro. The coal is very similar to that obtained from the Clutha mine, and there is no reason to doubt that the same formation, if not the same seam, continues between the two places, which are about fourteen miles apart.
The seam is nine feet thick, and is worked by a level drive in the side of a hill.
The present access to the mine is very bad, but a very small expenditure would construct a tramway for six miles to the township of Tokomairiro, which is the centre of a populous and important district that will be passed through by the proposed railway.
The Green Island and Saddle Hill Basin, which is within six miles of Dunedin, and about five or six square miles in extent, is another important development of this same coal formation.
Two of the principal seams, seven and nine feet in thickness, are worked at four different collieries, and though the quality is slightly inferior to that of the Clutha coal, yet, owing to the proximity to Dunedin, its consumption is very considerable; and it would, there is no doubt, be more universally used were it not for the great expense of cartage.
In 1864 the quantity produced from the mines in this district was about 4000 tons.
A third great extent of this formation on the eastern seaboard of the Province of Otago underlies the level country to the eastward of the Kakanui Mountains, and is in all probability the southern extremity of a formation that will be found to underlie the tertiary rocks that form the higher portions of the great Canterbury plains.
Coal of the description under consideration is also very extensively distributed throughout the interior of the Province of Otago, as local deposits in hollows of the surface of the older formations.
Such deposits, though generally of inferior quality to those above mentioned, have great local value, and are essential to the working of the gold fields on which there is a great deficiency of timber.
Pits have been opened in the vicinity of the principal gold diggings, and in some cases round the margins of the larger interior basins, the strata display a regularity and thickness that leads to the belief that they are of very considerable extent and will yield a steady supply.
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From the number of localities in the Province of Southland where this coal is excavated for local use, its extensive development in the Northern District, and indeed over the greater part of that Province, is extremely probable.
Some of the coal from the district in question is of very superior quality, and occurs in seams eight to twelve feet thick.
There are many other localities in New Zealand besides those already alluded to where valuable seams of Hydrous coal occur, but the above information is sufficient to show the singular importance of these deposits to the future development of the Colony, as, from their wide distribution and the applicability of this description of coal to most uses of mineral fuel--when compactness and economy of space is not the first consideration--the necessity for importing coal from other districts for local purposes will be obviated.
Under this group have been classed all the coal found in New Zealand, which resembles in quality the coal imported from England and Australia, which at the present time is the only fuel used in this Colony for the purpose of steam navigation.
Owing to the great and still progressive development of the steam coastal service in New Zealand, which in a great measure replaces the expensive works for internal communication, necessary in countries not favoured with so extensive a sea-board, it is very important to the future prosperity of the Colony that it should be independent of other countries for its supplies of steam coal. Already, with a population of two hundred thousand inhabitants, the sum of £160,000 is withdrawn from the Colony every year for this item, and spent principally in labour in a neighboring Colony, and for shipping expenses, neither of which are reproductive to New Zealand.
It is, therefore, satisfactory to find that coal exists in New Zealand adapted for the use of steam vessels on long sea voyages, and moreover that the supply is abundant, and occurs under circumstances that will ultimately admit of its being profitably worked, although there may be some difficulties, and, perhaps failures, in the first attempts.
The composition of the coal comprised in this group is very varied, but not more than is usual among coal seams from different coal fields in other countries,
The only point in which, as a class, they are deficient in any
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of the characters which have been laid down as requisite for a perfect steam coal 1 is in the solidity and toughness that enables the coal to withstand the constant attrition it must experience from the motion of the vessel. The consequence of this defect would be the formation of dross, the combustion of which is difficult without the use of close furnace bars, which greatly impair the draught.
This defect is, however, comparatively insignificant, and is more than compensated for (except in a few instances) by the purity of the coal, its tendency to cake, and the facility with which complete combustion can be effected, so that the loss by the formation of cinders will be much below the average.
Full particulars respecting the composition of the different varieties of Anhydrous coal are given in the Appendix to this Report, part of which has already been printed in the Supplement to the Jurors' Reports on the New Zealand Exhibition, 1865.
The most important development of the coal seams of this class is on the West Coast of the South Island, where the formation occurs resting on the surface of the metamorphic and crystalline rocks.
At Preservation Inlet, in the Province of Otago, and at various other points on the coast, this formation occurs, but without any valuable seams of coal, so far as we yet know, until the Grey River is reached; the coast to the south being principally formed either of the older rocks or of sub-alpine drifts and alluvium.
Prom the Grey to Cape Farewell this coal has been discovered at intervals, but whether or not the seams at these different localities are portions of the same formation, partially isolated by denudation, has not yet been determined.
The following information respecting the coal fields at the Grey River has been furnished by Dr. Haast.
At this locality the coal extends over an area which he has estimated at fifteen miles in length by six in width.
The coal seams are said to rise with a dip of from ten to thirty degrees from the sea level to an altitude of several thousand feet, so that they occur under circumstances most favourable for their being worked at a small cost, as neither shafts nor pumping machinery will be necessary.
There is no apparent disturbance of the beds, nor any reason to
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suppose that the whole of the coal in the above area may not be worked.
The number of workable seams that have been discovered is four, the main seam being fifteen feet three inches in thickness.
Only one mine has yet been opened up in this field on the north side of the River Grey, at seven miles from its mouth. It is a simple chamber opened in the fifteen feet seam, at ten feet above flood mark.
From this point the coal is supposed to extend on the rise for about four miles, in an easterly direction, the dip in the present mine being ten degrees to the west.
Arrangements are now being made for working the coal on the south side of the river, which is in the Province of Canterbury, and for the construction of a railway to convey it to a point on the river where it can be shipped in vessels of six to seven feet draught.
At the present time the great obstacle to the development of these coal mines is the high price of labour, owing to the attractions offered by the gold fields, but when this excitement has subsided a large portion of the present population of that district, which is estimated at fifteen thousand persons, will doubtless become permanent, and notwithstanding the present temporary check, the importance of these coal fields will be much sooner established than if the auriferous deposits had not been discovered, and the "Westland District had still remained as inaccessible as it was twelve months ago.
At present the output from the coal mine is about 250 to 300 tons per week, and is taken down the river in canoes and in 16 ton barges and delivered alongside the vessels at 40s. per ton. It has been used to a large extent on board the steam vessels that frequent the coast, and gives great satisfaction. A small quantity of this coal is also reported to have been tried in the Dunedin Gas Works, and to have yielded a large quantity, of illuminating gas.
Regarding the coal fields at the Buller River, detailed information may be found in the reports of Dr. Haast and Messrs. Rochford, Burnett, and Blackett.
The only outcrops of coal known in this district occur at altitudes of more than 1500 feet above the sea level, the strata resting upon a high narrow plateau that lies parallel with the coast, and extends though possibly not continuously, as far north as West Wanganui, a distance of eighty miles, where its outcrop again reaches the sea level as at the Grey.
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In the immediate neighbourhood of the Buller River the existence of workable coal seams is considered certain over an area of at least fifteen square miles.
Reckoning none of the seams having a less thickness than five feet, there is a total of thirty-eight feet of pure coal; and the quantity available in this one locality has been estimated at 200,000,000 tons.
Although the Buller Harbour is on the whole more favourable for shipping than the Grey, yet the greater expense of working the coal, on account of the altitude and distance from the shipping place at which the seams occur, would indicate the Grey coal field to be the most immediately available. The quality of the coal is practically identical from both localities, and is characterized among all other New Zealand coals by the small percentage of water which it contains, usually from 1 to 2 per cent. It also contains less than the usual amount of impurity, about 90 per cent of the coal being combustible, 30 to 35 per cent. of which is gaseous matter, leaving 65 per cent. of lustrous metallic coke, which possesses intense heating qualities.
As steam coal, its value has been fully established by a series of experiments made in 1865 with the trial boiler at Woolwich Dockyard. 2
The results given by Mr. Trickett, chief engineer of the dockyard, are extremely favourable to the Buller and Grey coal, even as compared with the Welsh and North of England coal; and he appends the following remarks to the tabulated results of his experiments:--
"The Grey coal cakes in burning, and makes a hollow fire forming a small quantity of light clinker that does not adhere to the bars. Light ash only falls through the fire-bars, and a considerable quantity of white ash passes up the chimney, leaving a dark grey sandy kind of dust in the tubes and fire-box. The smoke is small in quantity, and the coal is tender and likely to break small in being moved from ship to ship."
"The Buller coal is a more open burning coal, and does not cake 3 forming a rather closer clinker than the other; and leaves a sooty deposit in the tubes and fire-box, more like the Hartly (North of England) coal, and gives off a black smoke."
"No stoking tool was used in burning the samples of both kinds of coal, and nothing seems to be required, beyond throwing the coal
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on to the fires; and the quantity of each clinker is not greater than that of the North of England coal. The evaporative power of this coal is about the average of that of North of England coal as supplied to the service; but it is not quite so rapid, and requires a rather longer time to boil off a given quantity of water. The trial of the 17th November was made with the bars half-inch apart, the other trials with the bars about three-eighths of an inch apart."
And again Mr. Trickett writes:--
"I beg to report that additional trials have been made of the New Zealand coal, and a comparative statement is forwarded herewith. The mean result of ten trials of North Country coal and ten trials of Welsh coal at the same boiler are given for comparison, from which it will be seen that the New Zealand coal evaporates more water per pound of coal than the North of England or Welsh, but does not evaporate it so rapidly; or in other words a larger fire-grate is required in the same boiler to evaporate a given quantity of water per hour with New Zealand coal than would be required if North of England or Welsh coal were used."
In communicating this Report to the Nelson Government, Mr. Burnett has constructed four tables, showing the results obtained, in a condensed and simple form, and also giving for comparison a summary of the results of similar experiments performed also at Woolwich Dockyard, but on a previous occasion, upon New South Wales coal.
Only the second of Mr. Burnett's tables and his remarks are here quoted, as they are sufficient to show the relative value of the different coals experimented on.
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TABLE snowing the RELATIVE VALUE for Steam purposes of North of England, Welsh, New South Wales, and Grey and Buller Coal, calculated on the basis given by the trials of these Coals at Woolwich Dockyard, viz.:--If 100 lbs. of average North of England Coal will evaporate a given quantity of water in an hour, this Table shows how the same work can be done by the other Coals.
EXAMPLE OF CALCULATION--BULLER.
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The following remarks are by Mr. Burnett, on the Woolwich Reports of trials of Grey and Buller Coal, and the Tables calculated from these Reports, showing their relative value as compared with North of England, Welsh, and New South Wales Coal:--
"The samples of coal, both from the Grey and Buller, were taken from within a few feet of the outcrop, and almost close to the surface, and it is only fair to conclude (as indeed the recent working at the Grey has demonstrated) that the quality of the coal will improve as the works are continued further from the outcrop, and deeper below the surface.
"It is to be presumed that the North of England, Welsh, and New South Wales (being from actual working mines), would be a fair average of the mineral in its full perfection; and in the case of the two former, probably fresh from the mines, whereas that from the Grey and Buller was mere outcrop coal, not tested for more than sixteen months after it was worked, and after being broken and deteriorated by shipping, re-shipping, carting, packing, and conveying to the other side of the world; so it is only reasonable to conclude that samples of these coals, a moderate depth from the surface (such as will be produced when the mines are actually worked), tested under equally favourable circumstances, would contrast still better than they do at present.
"When the Grey and Buller coal was packed in boxes at Nelson, the dead small was taken out and put in bags, but was not intended to be sent to England; however, by mistake it was sent, and to this accident we are indebted for one of the most valuable results of these trials, viz., that the 'coal in bags' (see second Report), i.e. the dead small, is very nearly equal to any other part of the coal.
"This is a most important quality, as it does away with the necessity of screening, by which a considerable percentage of other coal is wasted: the small of Welsh coal particularly is almost useless.
"Another very valuable property is the small quantity of clinker and ash contained in this coal; and what little clinker there is does not stick to the bars. The amount of disagreeable labour saved by this can only be thoroughly appreciated by the working stoker. Indeed, it appears that no stoking whatever is required, 'but that a small increase of the water evaporated per hour is obtained when the fires are stoked.'
"This is shown very clearly in table No. IV., second part, where, in the trials of dead small, 6.11 per cent. more water is evaporated in a given time when the fires are stoked; so, it may be presumed, that had the coal in boxes been stoked, the result would nave been better in like proportion.
"Table No. IV. is a condensation of the information contained in the reports and tables, and shows, at a glance the comparative value of each kind of coal tested.
"It is interesting to compare the results of minute and elaborate trials at Woolwich, with the trials of the same coal on board local steamers in 1861, (published in the New Zealand Gazette, February 15, 1862,) for it will be seen that in almost every respect they agree exactly.
"There was only one trial of Buller coal, as only two tons were
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sent to England, owing to the difficulty of carrying it from the mine to the port without roads; but it will be seen that even this one trial shows a result almost equal to the best, as it is only 1 per cent. below Welch coal in evaporating water in a given time. (See table No. IV., second part.)
"It is rather singular that Mr. Trickett in his report says, 'the Buller coal does not cake,' whereas I know from experience that it does cake, but not so freely as the Grey. Possibly it was so much deteriorated before reaching Woolwich, that its caking qualities were destroyed.
"From all the trials, we have a right to conclude, that West Coast coal is 15 per cent. better than either average North of England, or New South Wales coal; and very much superior indeed, in the matter of clinker and ash.
"This is a matter of the utmost importance in the Panama service, particularly where the whole distance from Wellington to the Isthmus is to be performed by rather small steamers, without a coaling station.
"This is expected to occupy about twenty days, and as engines of five hundred horse power will probably consume about fifty tons a day, one thousand tons at least will be required for the run. Now, if West Coast coal was used, there would be a saving of one hundred and fifty tons on this, and, consequently, one hundred and fifty tons more space would be available for cargo and passengers. This of itself would be an important item in the balance-sheet of the Company.
Proceeding northwards from the Buller River this Anhydrous coal has been discovered in the Mokihinui, Heaphy, and most of the other streams that flow to the westward, and always apparently of the same useful description;--but the most important development of this formation which remains to be mentioned is that lying between West Wanganui harbour on the west side, and Pakawau on the east of the promontory that terminates in Cape Farewell. The coal formation is not however confined to the West Coast, as it has been found at the Batten and Wangapeka Rivers, which are at a distance of thirty miles from the coast and flow into Blind Bay. Mr. T. R. Hacket, Mining Engineer, informs me that, in West Wanganui, the coal seams occur at the sea level with a gentle southerly dip, and can be easily worked,--the total ascertained thickness of two contiguous seams being eight feet of available coal.
The quality is apparently inferior to that of the Buller and Grey coal, from the specimens analyzed (see Appendix): nevertheless it has been tested practically in steam vessels with satisfactory results, and systematic workings are about to be commenced, twenty cargoes having already been shipped from surface working between tide marks.
The harbour of West Wanganui is reported safe for vessels of ten
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to twelve feet draught, and is considered superior to either the Buller or Grey harbours.
At Pakawau, which is on the East Coast, at a distance of seven miles from West Wanganui, the coal seams have been explored and worked to a considerable extent, but up to the present time without any satisfactory results, on account of the irregularity of the strata and the mixed nature of the coal.
At Aorere, which is seven miles south of Pakawau, and equi-distant from the outcrop at West Wanganui, coal has been long known to exist, and lately a valuable seam has been discovered under circumstances favourable for its development.
At the Batten and Wangapeka Rivers, although the existence of the coal is established, the value of the seams is not clearly ascertained. The disposition of the coal fields along the western slope of the South Island, and their association with other sources of mineral wealth and large areas of valuable land, render it almost certain that the route that will be first adopted for railway communication will be by the west side of the mountains, and thus pass through districts that will afford employment to a condensed population.
Already sufficient information has been collected to make it certain that no insuperable engineering difficulties would be encountered in carrying such a scheme into effect.
When this railway has been constructed, it will afford the means of transport by which the coal produced in the Western fields can be economically distributed over the country.
From various estimates which have been made by competent engineers, there appears however to be no doubt that, even with all the present disadvantages, the coal from the Buller and Grey fields could be delivered to steam vessels in Cook Strait at a cheaper rate than the present price of the coal imported from New South Wales.
In addition to the coal fields on the West Coast of the Middle Island, extensive tracts of the same formation occur on the east side of the mountains, that contain seams of Anhydrous coal, which are however of no great thickness, and of very uncertain quality.
The best of these is at Shag Point, in the Province of Otago, where the coal occurs with the same fossiliferous strata as at Pakawau and the Grey River, but has more the composition of a non-caking cannel coal.
This coal, the principal seam of which is five feet thick, is mined
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and used to a small extent in the Province of Otago, but, so far as yet developed, has only local importance.
The coal mentioned in the Appendix as from the Kowai River, Malvern Hills, in Canterbury, is of excellent quality, but has not been discovered in workable seams.
The formation which has been reported on by Dr. Haast occupies a basin among the mountains, but in quite an accessible position. The strata dip at 60 deg. to 70 deg. and the breadth of their outcrop is described as 6000 ft.
This coal probably belongs to a lower series of coal measures than any of the above-mentioned Anhydrous coals, and to which the coal found at Waikawa, in the south-east of Otago, also belongs.
The extent of the coal formation in the last-mentioned district, consisting of indurated sandstones and conglomerates, is very great; and if good workable seams were discovered, this harbour would be a most favourable locality for shipment.
The only seams yet discovered, however, are less than twelve inches thick.
With reference to the occurrence of steam coal in the North Island, in the northern part of the Province of Auckland there is a large development of the same coal formation as that on the west coast of the South Island, containing seams of Anhydrous coal of considerable value, though their extent and persistence over large areas has not been established. This formation occupies the interior of the northern district, being separated from the sea on the east by ranges composed of slate rocks,--penetrated, however, by several excellent harbours--while on the west it is overlaid and cut off by recent tertiary and volcanic rocks.
The outcrop of this coal formation has been detected in a north and south line from fifty miles north of Auckland to Wangaroa Harbour, and there are also indications of its existence in the neighbourhood of Hokianga, on the west coast.
A large portion of the isolated mass of hills at the North Cape is also composed of this formation; and on the north side of the harbour of Parenga-renga, natural sections show these strata to be more than a thousand feet in thickness, although the coal is here only represented by very thin and worthless seams.
The only attempts to open mines in this section of the country have been made in the vicinity of the harbour of Wangarei, seventy
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miles north of Auckland, and on the Kawa-kawa River, which enters the Bay of Islands.
At Wangarei the mine, which is a private enterprise, was opened about twelve months since, and in March last was nearly in full working order. It is situated about three and a quarter miles to the north-west of the point to which a tidal river may be navigated by barges drawing six feet, by which it is proposed to take the coal six miles down the stream to a part in the harbour where wharfage can be constructed, alongside which the largest vessels could lie in safety.
The tramway to the upper barge wharf is now complete, the rails being for the present of wood, but the sleepers being sufficiently heavy to bear iron rails and steam traction at a future time if desired. The mine is opened as a drive which enters the face of a hill from a narrow gully, up which the tramway winds in a heavy cutting for the last half mile of its length, the first part being through a level scoria plain, with only a very gentle gradient and constructed at comparatively little expense.
The coal dips into the face of the hill, resting almost immediately on slate rocks and overlaid by marine strata of a newer formation, which again are capped by extensive sheets of Doleritic lava that form flat-topped hills, and occasionally rise into Trachytic cones.
The altitude of the mouth of the mine is 424 feet above the sea, and that of the volcanic plateau 664 feet.
The seam has a very gentle dip, and though traversed by small faults, can be worked under very advantageous circumstances, as a large extent of the seam is "won" level free.
As the discovery of a coal outcrop occurring under such exceptional circumstances, must be merely accidental, it is probable that several other mines may yet be opened in the neighbourhood, though no indication of the existence of coal seams has yet been obtained nearer than at Hikurangi, which is sixteen miles north of Wangarei.
At the Kawa-kawa River the coal seam which has been discovered, though of more valuable quality and thicker than that at Wangarei, can only be worked under less advantageous circumstances, as the small altitude above the sea at which the coal is found will make it necessary to have recourse, from the commencement of the operations, to shafting and pumping, both of which are obviated in the case of the Wangarei mine.
The coal is, however, so much superior in its heating qualities, in
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which respect it is second to none yet found in New Zealand, that before long it is certain to be extensively worked, and from the structure of the country there is reason to believe that it may yet be found in the same district under more favourable conditions for opening a mine, in which case the coal from this locality might be able to compete with that from the West Coast of the Middle Island.
The only work which has been executed is an experimental shaft, sixty feet in depth, and twenty yards from the out-crop, which is seventy-two feet above the bed of the Kawa-kawa River. In this shaft the thickness of the coal was 13.6 feet, only part of which was compact enough to bear working, but it might reasonably be expected to improve in this respect as the overlying strata increased in thickness with the dip.
About twenty-eight holes were also bored in the neighbourhood to a depth in some cases, of 130 feet, but in only one of them was the coal cut at such a distance from the outcrop as to afford any indication of the lay of the coal seam.
From the only locality where the coal has yet been discovered in this district a tramway of three miles is necessary to reach a point on the Kawa-kawa River, where there is sufficient draught of water for barges by which the coal might be conveyed down to where vessels can be loaded, but on account of the extremely friable nature of the coal it would be preferable to continue the tramway to this point in order to avoid transhipment. The distance would be nine miles, and on account of the heavy works requisite in some places it would be a very expensive undertaking. Notwithstanding these drawbacks, which may certainly affect the immediate development of this coal field in the present state of the Colony, there is every reason to expect that it will ultimately occupy a prominent position among the coal producing districts of New Zealand.
A summary of the most important features of the various localities where it has been proposed to work the Anhydrous coals in New Zealand is given in the following tabular form.
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Sufficient information as to the extent of the various coal seams in these localities has not yet been obtained to enable an estimate being shown in this table of the amount of coal existing in any of them; but by the most moderate computations founded on the extent of the coal formations, it would not be presuming too much on analogy to expect that there is not less than four thousand millions of tons of coal available in New Zealand.
The quantity of coal imported into New Zealand annually since 1853, as compared with the population, is shown in the following extract from the Statistics of the Colony, from which it will be seen that the consumption is steadily increasing, and that in the last year there has been a very marked fall in the price.
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QUANTITY and VALUE of COAL IMPORTED into New Zealand; also the Yearly REVENUE and POPULATION from 1853 to 1865.
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