PART I. GEOLOGICAL SKETCHES.
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Geological Structure of New Ulster.
In the present imperfect state of our know- of the Geology of New Zealand, as well as of the simple and compound minerals occurring in it, and until more data are collected respecting the various rock-formations and strata, considered as masses, to be found in the Northern Province, it is obviously impossible to produce anything at all perfect on the subject. We are here treading on new ground, and all, therefore, that the writer proposes, in the following brief memoir, is to give a mere sketch or outline of the leading features of some of the more important rock-formations and strata occurring in the Province, and this sketch being possibly filled up, at some future period, may thus become more perfect, as well as useful.
At first sight, New Zealand would appear, to a superficial observer, as a country in which fragments and ruins from the rest of the globe, have been confusedly heaped together, in an apparently chaotic mass, devoid of order or arrangement; but when it is more closely examined, its parts appear neither independent of arrangement, nor devoid of harmony and regularity; the various rocks and strata being found for the most part maintaining, wherever they occur, the same relative position as their original types in Europe, thus adding another proof, (if any were wanting), of the great fact and
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leading axiom in geology, that the order of succession or superposition of the Various rocks and strata, considered as masses, is never inverted.
Thus we find in New Zealand as in Europe that each of the great classes of rocks has a certain relative position of its own, the primary always occurring lowest in the series, and the transition, secondary and tertiary rocks being respectively next in the order of superposition. With regard to some of the unstratified rocks, however, such as modern volcanic rocks, lavas, basalts, and amygdaloids, it is to be observed that this regularity of position prevails in a much less degree, as might be inferred from their volcanic origin; these rocks often occurring in irregular masses lying upon the stratified rocks, in beds, or protruded between them in dykes or channels.
With respect to the primary unstratified or "plutonic"rocks of New Ulster, these are often found to range in wide irregular curved lines, enclosing large areas or basins, partially filled up by the stratified and sedimentary classes of rocks, as is the case over a large portion of Europe.
It appears highly probable that large portions of the northern and central parts of New Ulster must have been covered by the waters of the ocean, at the time when different portions of the primary and associated rocks were above the sea, for we find the tertiary deposits in those portions to consist frequently of detached basins, surrounded on all sides by primary and secondary rocks, and occupying a position in reference to the latter, very like that of the waters of lakes, inland seas, and gulfs, in relation to a continent.
That "plutonic action," as it has been termed, or the volcanic agency operating under pressure, and at considerable depths, has been developed on a large scale in the Province, is evident from the frequent disruptions and dislocations of the strata almost everywhere observable, and these apparent results are perfectly insignificant when compared with the contemporaneous changes which must have been going on out of sight, and which must remain hidden in the depths of the earth for ages. If, as is undoubted, all the stratified rocks were properly and originally horizontal, it is clear that all stratifications not horizontal, have been disturbed or upheaved by this agency, while it may be assumed that those remaining in a horizontal position have suffered no local disturbance, although they may, and no doubt have partaken, of a general elevatory movement.
It is, however, a matter for speculative inquiry to ascertain whether these changes of level took place at a time when the volcanic agency was in active, or as it has been termed "paroxysmal" energy in these Islands, producing, as on the coast of Chili, sudden elevations and depressions of short duration, followed by a permanent re-elevation of the land; or whether, as in the case of the Scandinavian Peninsula, the rise has been gradual and imperceptible, and continued through a long period of time up to the present day.
On this point our conjectures must necessarily be vague and uncertain, for although we have no proof that these Islands have been elevated since they were inhabited by man, we have around our shores many instances, and proofs of elevation of the land within a comparatively recent geological period, attested by raised beaches, and by beds of marine shells, occurring in some places at a considerable elevation above the level of the sea. The same remarks apply to the "lignite," or wood-coal of the tertiary strata of New Ulster, which is frequently found occupying an elevated position on the banks of rivers, as well as on the sea-coast; this lignite consists of wood, more or less carbonized, and in many instances the pieces, although much broken and water-worn, may easily be recognized as belonging to existing species of trees still growing on the Island. 1
That the strata in which these lignites are found, (and which abound in the Northern and Central parts of the Province,) have been subjected to an immense pressure, probably at great oceanic depths, is evident, and it is equally so that a considerable degree of heat must have been employed to produce the semi-carbonization of the wood, -- and yet we find this singular product occurring at various elevations, in seams varying from three inches to four feet in thickness, and overlaid by thick strata of loam and argillacious schistus, in formations of tertiary clay and sandstone.
The direction of the principal mountain ranges of New Ulster has a meridian trend, varying from North North East and South South West, to North North West and South South East. In this respect their direction does not much vary from that of the greater part of mountain chains in various quarters of the world:-- thus it is nearly parallel with the great chain of the Andes, and does not much differ from the great Australian Cordillera, which has also a meridian tendency or trend, ranging from North to North East; or from the mountain-chain of New Caledonia, which, according to a recent writer and talented geologist, (Rev. Mr. Clarke,) "together with New Zealand, may be considered as merely outlying summits of the
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great submerged land of which the Australian Cordillera is the main parallel."
Respecting the formation of the mountain chains of New Zealand, the theory of M. Elie de Beaumont, an acute French geologist, in reference to the mountain chains of Europe, would appear to be partly applicable. This theory embraces the following points:--
1. That, in the history of the earth, long periods of comparative repose, during which the deposition of sedimentary matter went on in regular continuity, have been interrupted by short periods of "paroxysmal" violence.
2. That, during each of these periods of disturbance, great numbers of mountain chains, in various parts of the world, have been formed suddenly.
3. That all the chains of each paroxysmal period have one uniform direction, being parallel or nearly parallel to each other, even when situated in remote regions of the world.
4. That these paroxysmal disturbances which have occurred at intervals, from the remotest geological epochs, may be renewed, and the present state of repose may be broken by the sudden elevation of other parallel chains of mountains.
Adopting therefore this theory, 2 that the parallelism of mountain chains is to be considered as a proof that they were elevated at the same geological epoch, it would follow that the New Zealand mountain-chain must be considered contemporaneous with that of the South American and Australian Cordilleras, and also with the mountain-range of New Caledonia. Further investigation however is required to confirm this supposition, for although the older rocks of all these countries are identical, and that the mountain-ranges, composed of primary rocks, have all a similar or nearly similar tendency, yet it does not necessarily follow that all these chains should have been elevated at precisely the same geological epoch.
Extinct Volcanos, and Volcanic Rocks.
Although volcanic action, or the ejection of lava, scoria, stones, and melted rocks, by means of gases and vapours, together with the action of earthquakes, which are themselves caused by the volcanic agency, where it does not find a vent, have unquestionably taken place in New Zealand from very remote periods, we possess no positive records as to the antiquity of the numerous igneous rocks which we find covering an extensive area in New Ulster, and which we immediately recognise as being the products of fire, from their exact resemblance to those which are produced by modern active volcanos. From the fact, however, of a large portion of these rocks covering the tertiary strata, it may be inferred that most, if not all of these igneous rocks may be referred to the tertiary period immediately antecedent to the recent epoch, as it is only among the tertiary strata that we meet with lavas which we can be sure were ejected on dry land.
The general character and appearances presented by the volcanic rocks of New Ulster do not differ materially from those found in many parts of the world, where volcanos have formerly existed, but which are not now in a state of activity, such as in central France, at Auvergne, and on the banks of the Rhine at Eifel, where the observer finds conical heaps of scoriaceous cinders and ashes, with lines of lava diverging from them, being the products of volcanic energy which has slumbered from the earliest period of recorded history.
Most of the igneous rocks of the period referred to, appear to have been the products of sudden paroxysms of volcanic energy, and to have burst through the sedimentary and marine strata of the tertiary epoch, covering in many parts extensive areas.
In the group of extinct volcanos found in the vicinity of Auckland, the cones, the craters, and the lava-currents still remain perfect in many instances, whilst in others, the volcanic cones are usually truncated at the summit, where the crater is found almost entire, the lava having issued from one side, generally facing the North, where the cone has been broken down, and the lava has flowed out. In some of them, no traces of a lava current are to be found, but large masses of black vesicular lava in blocks of various sizes, are found at and near the base: these appearances would seem therefore to indicate that the volcanic orifices have given vent to gaseous explosions, accompanied by occasional jets of lava and melted rocks, with showers of volcanic sand and ashes. The hills are for the most part composed of loose scoria, blocks of basaltic lava, with puzzuolana and other volcanic products.
Some observers have remarked that hills of such incoherent materials as compose these extinct volcanic cones, cannot be of any very great antiquity, because the action of the atmosphere, and of heavy rains, would wash away and abrade the materials of which they are composed:-- but their seems to be no foundation for this supposition, nor is there any reason to suppose that these hills have undergone any great alteration or abrasion of their surfaces since the period of their formation; as, owing to the porous nature of their component materials, the water which falls upon them is almost immediately absorbed.
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Concerning the original formation of these volcanic cones, we can only reason from the nature of the substances they present to us: most, if not all, of them are undoubtedly wholly the product of the matter ejected during eruptions, consisting of slag or scoria, ashes and basaltic lava, with occasional patches of pumice, and they exhibit all the external volcanic appearances which are usually to be seen in active volcanos. The "trappean" or step-like form of many of them is remarkable, and almost appears, in some instances, to have been produced by art.
Besides these masses of igneous rocks which have burst through the sedimentary deposits which surround Auckland, producing great derangement, fracture and alteration in the beds which they traverse, there are indications of igneous action contemporaneous with the formation of the strata, but on this point our conjectures are uncertain.
If we compare modern volcanic rocks, such as porous lava, scoria, pumice, and some others, with basalt, trachyte and other trappean rocks nearly resembling them in composition, we find that one of the principal differences consists in the greater degree of compactness in the latter. To explain the cause of this difference, it must be borne in mind that the same mineral substances, being in a state of fusion, and cooling under different circumstances, will assume totally different appearances: thus a mass of fused volcanic matter, when allowed to cool rapidly, forms a substance of a vitreous or glassy nature, somewhat similar to the "slags" produced in a glass-furnace. Obsidian, or as it is sometimes called, "volcanic glass," is a substance of this nature, and results from a very rapid cooling of the fluid mass. On the other hand, when the cooling is very slow, a stony and crystalline arrangement of the particles takes place, as in basalt, which is found in New Ulster in beds, in dykes and occasionally in columnar masses.
The igneous origin of these rocks was never questioned by those geologists who had opportunities of studying the science in countries in which volcanic action was largely developed, yet it is a singular fact that, for many years, the aqueous origin of basalt was fiercely maintained by geologists of the Wernerian school.
The name of basalt was formerly given to any dark-coloured rock, having a crystalline and columnar structure, but the term is now limited to a dense compact mass of hornblende or augite, in which crystals of felspar are visible; as this latter increases in quantity, and the hornblende or augite becomes coarser grained, it passes into greenstone, which, like basalt, occurs in New Ulster in "dykes" and in interposed and overlying masses.
Most of the extinct volcanos of New Ulster have ejected basaltic lavas: but the basaltic rocks occurring in hills of a round form, and in tabular masses, have most probably been formed under the pressure of the sea or of other strata, and have been subsequently elevated to the surface.
Basaltic rocks are found at several parts of the coast of New Ulster, particularly in the vicinity of the North Cape, and thence to Cape Maria Van Diemen. This Cape which forms the north-west extremity of the Province, is formed of detached rocks of a hard conglomerate, composed of boulders of basaltic lava, amygdaloidal basalt, greenstone and Lydian stone. (Dieffenbach.)
From Cape Maria Van Diemen along the western coast a long line of sand hills alternates with a few cliffy promontories, consisting either of a hard basaltic lava, in irregular masses, or of a reddish loamy earth with layers of lignite. (Ditto.)
On the banks of the Wairoa are steep hillocks of basalt, and on the right shore, and towards the sea-coast, is a soft ferruginous sand-stone; inside and round the North head the cliffs expose layers of lignite, generally 4 feet in thickness, and superimposed to the height of about 20 feet by a white and slightly consolidated sand, which softens by exposure to the water, and on near examination, is found to consist of decomposed pumice stone, of which large globular boulders are still compact. Extensive beds of the same lignite 4 feet in thickness, and overlaid by sandstone, are likewise found round the south head of Hokianga; they are then lost beneath the surface, but appear again near the north head of the Kaipara. (Ditto.)
The north headland at the entrance of the river Waitemata, is formed by a round hill (Takapuna) about 200 feet high, composed of a hard basaltic rock, which has burst through the sandstone and other sedimentary rocks with which it is in contact. The other hill (Takarunga) at a little distance from it, consists chiefly of black and reddish vesicular lava, and has on its summit, a crater, partially broken in.
Volcanic Action in New Ulster.
Most geologists are aware of the difficulty of defining the limits between active and extinct volcanos, or how long an interval of rest may entitle us to consider a volcano extinct, or the volcanic action to have entirely ceased in a country in which it was formerly in active operation.
Although many centuries have doubtless elapsed since the New Zealand volcanos were in a state of activity, no history or even tradition being in existence of their eruption, it by no means therefore follows that their now dormant fires are for ever extinguished, or that they may not again awake to destructive energy.
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We know for instance, that in the first century of the Christian era, Vesuvius had been in a state of quiescence from the remotest periods to which tradition at that time extended, when suddenly and without any previous intimation, its fires burst forth again, carrying ruin and destruction before them, and engulphing cities in its lava and ashes.
We also know that the island of Ischia was the scene of volcanic eruption in those early days when Vesuvius was quiescent, and that for a period of seventeen centuries during which subterranean fires have found a vent in that mountain, Ischia, with only one exception has remained in a state of repose.
Tho same alternation therefore of energy and repose may prevail in the volcanic system of these islands, and new lines of eruptive vents may, at some future period, be opened, preceded by convulsive movements and earthquakes of a similar nature to those which have been experienced at different periods, in the southern portion of the Northern Island.
These convulsions of the crust of the earth, and which may be regarded as a general effect of the same cause which produces volcanic eruptions, appear in New Zealand to be confined to a particular tract, which is comprised to the southward and eastward of a line drawn from about Tauranga, in the Bay of Plenty, to the great inland chain of the Ruawahaine, and extending to Tongoriro; the line proceeds thence in a westerly direction, ending near Cape Egmont at Taranaki.
Earthquakes of a most severe character have occurred within the memory of the present native and European inhabitants, in various parts of New Zealand, bordering on Cook's Straits, especially in Queen Charlotte's Sound, in the Middle Island.
In May, 1840, several severe shocks were experienced at Port Nicholson, and in 1841 in New Plymouth or Taranaki, three shocks occurred, one of which was so severe, that had there been any brick or stone buildings in the settlement they would, in all probability, have been ruined.
The calamitous and destructive shocks which took place at Port Nicholson in October and November of 1848, are still fresh in the memory of the inhabitants. The shocks continued during a period of more than six weeks, shattering nearly all the brick buildings in the settlement, and causing much destruction of property.
It would therefore appear that the whole of the Southern Province of New Munster, is still under the influence of the volcanic agency producing subterraneous convulsions, and that in the Northern Province, this action appears to be confined to the Taranaki district, and the country from Taupo to Tauranga, including the line of coast to the eastward.
To the north of this line, the volcanic action appears to have entirely ceased, if we except certain thermal springs which rise in several localities in New Ulster, and which although not situated in volcanic districts, indicate that a channel of communication has been opened with the interior of the earth, at some former period of local convulsion. The whole of the district adjacent to the inland lakes of Taupo and Roturoa, exhibits the effects of deep-seated volcanic action; earthquakes, although slight, are of frequent occurrence, both in the vicinity of the lakes, 3 and at several parts of the coast, adjacent to Wakatane.
Numerous thermal springs surround the lakes, and maintain an unvarying temperature throughout the year; some of them nearly attain the temperature of boiling water, and are used by the natives for cooking purposes. These springs are mostly charged with carbonate of lime, carbonic acid and silica, the carbonate of lime being precipitated from some of them, and forming masses and concretions of a peculiar limestone.
White Island, in the Bay of Plenty, opposite to Wakatane, is chiefly composed of volcanic products: obsidian, pumice, and sulphur, are found in large quantities on its shores, and on its summit there is said to be a small lake, the water of which is highly impregnated with sulphuric acid, and sulphuretted hydrogen: thus we have the singular fact of aqueous sulphuric acid, formed by a natural process.
The "Souffriere," or Solfatara at this Island, (improperly termed a volcano), never ejects cinders, stones, or melted lava, but simply gives vent to sulphureous, watery and acid vapours and gases, which on being condensed, leave a considerable deposit of sulphur.
Some geologists contend that the upheaving force of earthquakes, and of volcanic agency generally, was more energetic during remote periods of the world's history, and that it has since been gradually on the decline; that in fact, the present is an "era of repose," and that existing causes, now in operation, are insufficient to effect any great changes of the earth's surface, or of the permanency of existing continents.
On this point it is necessary to observe, that it is only by carefully considering the
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combined action of all the agents and causes of change, now in operation, that we can hope to explain the complicated appearances which are exhibited in the earth's crust.
When we have seen within the last century, numerous and convincing proofs of the undiminished force of the volcanic agency in various parts of the world, --when we know that a vast area in Scandinavia has been slowly rising for centuries; when we have seen that a considerable tract of land in the Delta of the Indus has been submerged; that an adjacent part of the same district, upwards of fifty miles in length, by sixteen miles in breadth, has been permanently upraised to the height of ten feet above its former level; when we know, from undoubted authority that within the last thirty years, one earthquake has permanently raised the coast of Chili for one hundred miles, to the average height of three feet, and that there exist proofs of a permanent elevation of part of the same coast, within a recent period, to the height of twenty-four feet above the former level; when we review all these phenomena, why should we suppose that the natural causes which have worked successive changes in the earth's crust, are not still in operation with undiminished energy?
If we examine the innumerable islands and archipelagoes which are scattered over the North and South Pacific, we shall find that this immense ocean, particularly in equatorial latitudes, is one vast theatre of volcanic action, developed on a scale unknown in European countries or seas. The entire Phillippines, and Marian Islands, the Moluccas, Java, Sumatra, and Borneo, Queen Charlotte's Islands, the New Hebrides, New Caledonia, the Friendly, the Navigators, the Society and the Sandwich Islands, are all composed of volcanic rocks, with numerous active vents here and there interposed. Some of them attain an elevation of 10,000 feet or more above the level of the sea, and bear evident marks of having been elevated by successive volcanic eruptions. 4
In the event of the volcanic system of New Zealand again awaking; to active energy, and opening new lines of eruptive vents, or renewing the former ones, an event which the experience of other countries teaches us is by no means improbable, the great central mountain of Tongoriro would probably form the nucleus of this action, which might be expected to be most energetic along a line extending in a north-east direction to Mount Edgecombe or Putawaki, in the Bay of Plenty, and westerly from Tongoriro to the great volcanic cone of Mount Egmont, which rises, in solitary grandeur, to the height of nearly 10,000 feet above the sea-level, its lofty summit being capped with perpetual snow.
With respect to this mountain, it is probably the most ancient of the New Zealand extinct volcanos, and its igneous products extend for a great distance from its base. Pumice and scoria are found in great abundance near it, and vast quantities of iron sand are brought down by the streams to the sea-shore, where it forms deposits of two to three feet in thickness near the mouths of all the rivers and streams emptying themselves at this part of the coast, extending from Taranaki to the Waikato, a distance of nearly one hundred miles.
Of the Rocks commonly called Primary, Secondary, and Tertiary, occurring in New Ulster.
Arrangements of the stratified and unstratified rocks have been drawn up by several geological writers, with various degrees of clearness and success, those of an early date being now mostly obsolete from the advanced state of science. The classifications of Sir H. de la Beche, and of Sir Charles Lyell, are those now most commonly adopted, and, in the following pages, will be chiefly followed.
The grand divisions of the formations of all epochs are "hypogene" (plutonic and metamorphic), volcanic, aqueous, and alluvial. The "hypogene," or nether-formed rocks are those crystalline masses which, for the most part, form the nuclei of great mountain chains; the "plutonic" being those in which no traces of stratification are visible, whilst the altered or "metamorphic" rocks are distinguishable by their being commonly arranged in strata. The volcanic rocks are the products of ancient or existing volcanos; the "aqueous" formations are those deposited by the sea, or found at the bottom of lakes; and the "alluvial" deposits are those brought down by rivers and streams, and deposited in estuaries and valleys.
The unstratified crystalline rocks have been called "plutonic," from the opinion that they were formed by igneous action at great depths, and include granite, syenite, green-stone, hypersthene rock, serpentine and diallage rock, basalt, porphyry, and a few others;
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whilst the altered or "metamorphic" series comprise gneiss, mica schist, chlorite schist, argillaceous schist, hornblende schist, talcose slate, quartz, and some others.
The plutonic and metamorphic rocks together occupy probably nearly three-fifths of the area of the Province, and the remaining two-fifths are covered by tertiary and recent strata, which are of great extent in the central parts of the island, whilst portions are found bordering the sea-coast at different points. 5
Of the former, granite with its associated rocks would naturally claim our first attention.
Granite was formerly considered to be the oldest fundamental rock of the globe, on which all others rested; but although some granites are undoubtedly of a high degree of antiquity, it is now rendered certain, by the late researches of eminent geologists, that others have been formed at a comparatively recent period, in some cases even posterior to the formation of the fossiliferous and stratified rocks, in which granite has been found in veins protruded among them, in the same manner as basalt and other igneous rocks. Werner considered that there were three sorts or ages of granite: 1st, the primitive; 2nd, a newer formation which traverses other primitive rocks in veins; and, 3rd, the newest granite resting on some of the other primitive rooks.
The ordinary granite of New Ulster consists of the usual compound of quartz, felspar, and mica, but sometimes hornblende is substituted for mica. In some places a variety occurs which is composed of felspar and hornblende, alone, but this would probably, by mineralogists, be classed under the head of that indistinct rock called "greenstone," which, although termed green, occurs of various shades of colour, as brown, black, and grey.
Granite occurs in masses with gneiss in the neighbourhood of Cape Colville, where it forms, with other hypogene rocks, a mountainous chain, running about N. N. West, and S. S. East, and attaining its greatest elevation near the Cape, at which point the highest part of the range is about 1,500 feet in height.
Granite is also found at Otea, or the Great Barrier Island, which is probably a continuation of the Cape Colville range, as the island has nearly the same direction or trend. This rock, probably, forms also the body of the Little Barrier Island, and some of the other Islands in its vicinity, as the Pokohinous, the Morotiti and Fanal Islands.
(5) In New South Wales, according to Mr. Strzelecki, the space occupied by the crystalline rocks is to that of the sedimentary rocks as 3 to 1. -- In Van Diemen's Land, according to the same authority, the proportion is as 7 to 1.
The granite found in the neighbourhood of Cape Colville is in general fine grained, and without any appearance of stratification; this would therefore, by geologists, be considered as belonging to the earliest formation of this rock.
The rock termed "gneiss" is composed of the same ingredients as granite, and its texture is equally crystalline. This rock also occurs near Cape Colville, and at the Barrier Island, and is almost undistinguishable from granite, except in the fact of its occurring in beds and tabular masses.
The remarkable peak, called the "Castle Peak," situate on the same range, near to Coromandel harbour, is probably composed of this rock, or of granite protruding through the argillaceous rocks of which the range is at this part chiefly composed.
The country in the vicinity of Cape Colville exhibits a great variety of the hypogene rocks, both plutonic and metamorphic, including granite, syenite, greenstone, claystone and claystone porphyry, clinkstone, compact felspar and felspar porphyry. The metamorphic rocks in the same neighbourhood include gneiss, mica schist, chlorite schist, argillaceous schist, clay slate, hornblende slate, talcose slate and quartz rock.
These rocks are found for the most part maintaining the same relative position as their originals in Europe; thus we find the clay-slate at Cape Colville reposing on the granite at various angles. We also find this clay-slate intersected by numerous dykes or channels of a porphyritic rock or "elvan," and we find both rocks traversed by veins of quartz and by "lodes," which at some points are metalliferous, and contain the ores of copper, lead and iron.
Crystallized Quartz is found at various parts of the same range, and large masses of Quartz rock, which appears, indeed, to form at some places, the body of the range. On this subject it is to be observed, that it is in, general extremely difficult to ascertain correctly the structure and composition of elevated mountain chains in New Zealand. The density of the vegetation upon them is one great obstacle, but if, on ascending them, it is found that their summits are crowned by a certain rock, we have a right to conclude from analogy, that the same rock which forms the summit, composes the body of the mountain.
Although much diversity of appearance occurs in mountains, consisting of alternate masses of plutonic and metamorphic rocks, and as these rocks suffer in different degrees by exposure to the action of the elements, this circumstance contributes to increase the difficulty. But if it be found that their summits are composed principally of one kind of rock, as of granite for instance, although other kinds may be found in the immediate vicinity, we have a right to conclude
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that the preponderating and uppermost rock forms the body of the range.
The aspect and outline of a mountain range, viewed at a distance, gives also some approximative idea of its formation; thus if the summit forms elevated peaks, sometimes appearing like the ruins of towers and fortifications, granite or some of its associated rocks, is usually found to he its chief component. But if its summit is rounded, with occasional terraces or steps, appearing in some instances, as if formed by art, we may well conclude that such elevations belong to the basaltic or "trappean" formations. 6
The northern extremity of New Ulster, extending from Cape Maria Van Diemen to the North Cape, and southerly towards Cape Brett, is composed of a great variety of rocks, as amygdaloidal basalt, mica-slate, greenstone, and some conglomerates.
This portion of the island being exposed to the uncontrolled violence of the Pacific wave, is the cause of the abrasion and decomposition of many of the rocks lining this part of the coast. The prevalence of strong northerly and easterly gales causes a heavy swell on the coast, whilst there is a strong current setting at the same time to the northward, which increases the sea, and the waves perpetually battering against the rocky barrier, form deep caves and lofty arches, hollowed out of the steep cliffs, whilst almost every promontory ends in a cluster of rocks formed in various shapes, as in pinnacles, columns, obelisks, &c.
The Eastern Coast from the North Cape to the north head of the harbour of Parenga-renga, is formed by perpendicular cliffs of volcanic conglomerate, sometimes alternating with other rocks of argillaceous schist, and some others. Part of this coast is occupied by a hard grey sandstone, which can be traced across the neck of land separating the harbour of Parenga-renga from the sea. On both sides it is included by the conglomerate. In this sandstone a small seam of good coal is found a few feet in length, and about 1 1/2 inch in breadth. This coal, although in small quantity, is in this case a true coal, and not the brown coal or lignite, which is so common in New Zealand.
The secondary formations are commonly characterized by containing fossils of extinct species of shells, fishes, &c, and present no remains of land animals. 7 They are for the most part oceanic deposits, having arisen from causes far more general than those which have produced the tertiary strata. We find in them very similar repetitions of sandy, clayey, and calcareous deposits to those of the tertiary scries, but generally in a state of much greater induration, forming compact sandstones, shales, clay-slates, and limestones; and the unimportant lignites of the tertiary strata, expand into the thick and valuable beds of coal which characterize that portion of the series termed the "coal-measures."
The various calcareous rocks form an important feature in secondary formations, and consist of limestones, including chalk and marble, the oolites, gypsum, &c.
Limestone, with its associated rocks, although one of the most abundant mineral substances in Europe, where it forms extensive mountainous chains and thick beds, is not an abundant rock in New Ulster, where in fact, as in Australia, some of the secondary series of rocks appear to be entirely wanting.
Calcareous rocks occur in mass in the estuary of Kawia, on the west coast of New Ulster, and can be examined on the left bank of the Awaroa, and on the south side of the harbour of Kawia. The limestone cliffs are corroded in various ways; chasms have been formed by the dripping water, and stalactites hang from their sides and roof. The nature of the fossils which are found in this formation, and which consist of great numbers of a large "ostrea," often a foot in length, and of the "terebratula," in an excellent state of preservation, would seem to place this formation in the tertiary series of rocks; they are such, however, as are found in formations of all ages. (Dieffenbach.)
In the Bay of Tauranga, a marly limestone in horizontal strata appears on the sides of the hills; it breaks into slabs about an inch thick. To the northward, the hills present a perpendicular escardment, and the limestone displays the interesting phenomenon of a dendritic dyke of whinstone (Lydian stone) injected into the mass. The limestone is altered where in contact with it, and inclines at an angle of about 40 degrees: a few paces from this, the strata are again horizontal, (ditto) Again, we learn from the same writer, that about two miles from the south head of Wangaroa
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harbour, a beautiful red and variegated marble is found on the coast, of a close fine grain, and in sufficient quantity to become of importance for domestic architecture, at some future period. This marble occurs in connexion with chloritic and argillaceous slate, and seems to belong to the secondary or transition series, if we may judge from its mineral character, for it does not contain any fossils.
This marble belongs probably to the greywacke limestone formation, or as it is sometimes called "transition" limestone, forming a portion of the greywacke series, in which it often occurs in irregular beds, and of various colours, as black, brown, white and red, and frequently veined or variegated with these colours. The pure white, or statuary marble belongs however to the primary formation of rocks, being nearly a pure carbonate of lime; its texture is compact and granular, and some varieties of the primary limestone are called "saccharoidal," from their resemblance to white sugar.
Common limestone of a loose texture, and of a dull and earthly fracture occurs also at Wangarei, where it is found in a stratified deposit, alternating with sandstones, shales, &c. The calcareous beds are however very impure.
The deposits classed together under the name of the "oolitic" group, are of a very complicated character, the predominating feature consisting of a limestone, formed by small spheroidal particles, varying from the size of a poppy-seed to that of a pea, and held together by a cement chiefly composed of calcareous matter. The series is subdivided into three portions, which have been named from their relative situation, the upper, the middle, and the lower oolite, each of which has its peculiar characteristics.
The whole formation of the oolites rests upon the great argillaceous deposit, termed the "lias," which is itself subdivided into upper lias shale, marlstone, lower lias shale, and limestone.
Like most members of the oolitic series, the lias is remarkable for the number and variety of its fossils. It is evidently a marine deposit, and must have been produced, like the rest of the oolitic strata, by a slow and uninterrupted action favorable both to the existence and preservation of animal life, as would appear from the immense number of marine shells and fossil remains found abundantly in it. With the lowest stratum of the lias, this abundance ceases, and the "new red-sandstone," which comes immediately below it, contains scarcely a vestige of animal or vegetable existence, thus proving the two different epochs of their formation.
With respect to this rock, (new red sandstone) with its associated red marl, it may be observed that the districts formed by it are easily recognised by the prevailing redness of the soil, and the deep red tint of the substrata, wherever exposed to view. This rock is so named in order to distinguish it from a sandstone very similar in many respects, but belonging to a much more ancient geological period, and thence named the "old red sandstone."
In the new red sandstone formation, four subdivisions may generally be recognized. The upper portion of the mass usually consists of a reddish clay or marl, below which is a soft micaceous sandstone, frequently of a deep red colour, but occasionally of a whitish or yellowish tint. The sandstone is underlaid by thin calcareous beds of a conglomerate nature, the whole generally reposing on a coarse siliceous conglomerate, composed of the fragments of older rocks.
The stone commonly known by the name of Matakana stone, from the district of that name, situated in the Gulf of Houraki, appears to belong to the oolitic sandstone formation. Although used as a building stone, it is hardly compact enough to form a good and durable stone, for building purposes, the sandstone being composed of siliceous grains, not very firmly cemented together, and tinted by the per oxide of iron. It appears, however, to harden by exposure to the weather.
A better description of stone belonging to the same series, is found at Mercury Bay, this stone is a freestone, which is cut readily when first taken out of the quarry, and subsequently becomes harder. It appears to be well adapted for building purposes, and for constructing piers, quays, and bridges.
The district of Matakana above mentioned, having recently been the scene of an experiment to ascertain the existence or nonexistence of coal, of the existence of which, in that locality, many persons entertained a confident belief; it may not be out of place here to advert to it, and also to the circumstances and conditions, under which coal is found in other countries.
It is well known that in Europe, in America, and other parts of the world, coal is almost everywhere accompanied by the same kind of rock, a knowledge of which is essential, wherever we would seek for this valuable mineral, in order to avoid attempts or experiments generally useless and always expensive. It is almost needless to observe that coal is never found in rocks of the primary formation, nor is it found among those of the more recent or tertiary formations, such as incoherent beds of sand, gravel, white sandstone, &c. In some of these beds, it is true, seams of lignite are found, but this substance must not be confounded with coal, as has sometimes been the case, both in New Zealand and in other countries.
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Many fruitless trials have been made for coal, in the black slate clay, and lias rocks, by ignorant miners, who mistook those rocks for the slaty clay and shale which form a principal feature in the "coal-measures." The bituminous shale and lignite found in the first named rocks, bear to the casual observer, some appearance of imperfect coal, and these deceptive appearances have occasioned expensive trials, and waste of capital in localities where, as at Matakana, it would be evident to any one at all versed in geology, that there existed not the least probability of obtaining coal.
Among the rocks composing the coal measures of England, we generally find the following order of superposition.
1. Micaceous and ferruginous sandstone, often very coarse grained.
2. Clayslates and mica-slates, with impressions of fish and vegetables, generally belonging to the grasses and ferns.
3. Strata of marl, limestone, and indurated clay.
4. A kind of secondary argillaceous rock, containing fossilized branches, roots, and even whole trees.
5. Argillaceous iron-ore.
6. Beds of pebbles, in a ferruginous sand.
The coal of this formation is found in strata alternating with strata of the rocks just mentioned, and which are indistinctly seen above and below the coal strata or seams; it appears that in general the contiguous rock both above and below the coal, is slate, but that below, the coal often differs from that which is above it; and what appears singular, it has been observed that the overlying slate is impregnated with bitumen, whilst the underlying slate contains none.
Of all the substances which may cover and conceal a bed of coal, the most common is a kind of indurated clay, very hard and tenacious, and more or less mixed with sand, gravel, and stones. This mixture is often almost as hard as a rock, and is formed of the debris of the neighbouring rocks, being sometimes from 30 to 40 yards in thickness. It frequently contains a great quantity of pieces of coal, which is generally an indication of the existence of a bed of coal in the neighbourhood. Generally speaking, the strata of coal, as well as those of the accompanying rocks, crop out some where, but as the upper coal strata are commonly of trifling thickness, its outcroppings are not very easily recognized.
The varieties of coal are numerous, but they may all be referred to two principal divisions. The first contains bitumen and carbon in various proportions, but the bitumen predominates; the second contains little or no bitumen, but is wholly composed of carbon, and a little earthy matter. The first kind is called black or "foliated" coal, and often, from its locality, "Newcastle coal." This species of coal burns with considerable flame and smoke, is highly bituminous, and gives out a large quantity of gaseous matter whilst burning, being in fact carburetted hydrogen gas in an impure state. The second kind of coal is known by the name of "anthracite," or stone-coal. It is also frequently called Welsh coal, or Kilkenny coal, from the localities where it is most abundantly found in Wales and Ireland. This species of coal, unlike the former, burns almost without flame, and with very little smoke. It consists chiefly of carbon, seme specimens containing as much as 92 per cent.
The largest known coal-field in New Ulster is found in the valley of the Waikato, where a very large deposit exists, and, according to the statement of the Surveyor General, who personally inspected this district in 1846, that officer gives it as his opinion that coal will ultimately be found to extend over one hundred square miles of the valley of the Waikato.
The following extract from a report of Mr. Ligar, published in the Government Gazette, in 1847, shews the extent and importance of this valuable deposit.
"I examined the two places Where the coal crops out, and found the seam to be six feet thick, and of good quality. One of these places is within 300 yards of the Waikato, and the seam is there elevated 200 feet above the river. Judging from the other places where the coal is also found, and from the formation of the country, I have no doubt but that coal will, ultimately, be found to extend over one hundred square miles of the valley of the Waikato, north of Kaitotihe."
So large an extent of workable coal must, unquestionably, prove of the greatest value to the Province, forming, as it will do, the great storehouse of fuel for future ages. It will no doubt appear superfluous to point out the vast utility and importance of the series of rocks comprised under the name of coal-measures, yet there are probably many persons who are scarcely aware of the full extent of the advantages which Great Britain has derived from her geological structure embracing such valuable and extensive deposits of this mineral. It has been observed by an able writer, speaking of the coal-measures of Great Britain, -- "The manufacturing industry of this Island, colossal as is the fabric which it has raised, rests principally on no other base than our fortunate position with regard to the rocks of this series:-- should our coal-mines ever be exhausted, it would melt away at once." (Burr's Geology.)
The specimens from the Waikato District exhibit a straight, laminated, or fibrous fracture, and a compact shining surface. The colour is almost a perfect black; it is generally brittle, and when exposed to the action of fire, burns without caking, and with little
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or no smoke or flame. These characteristics would therefore seem to mark this coal as belonging to the anthracite or stone-coal variety. Other specimens may however prove more bituminous, but those examined appear to consist chiefly of carbon, being in fact coal deprived of its volatile matter or bitumen, and converted into a species of coke by subterranean calcination. Coal is also found again at Mokau, on the banks of the river of that name, about 30 miles from its mouth, and is probably a continuation of the same bed or deposit as that of the Waikato coal- basin.
A knowledge of the general geological structure of New Zealand will no doubt one day, which it is to be hoped is not far distant, enable the geologists of this country to direct the search for coal in given rocks, and to advise the discontinuance of it in others, precisely as English geologists would advise the search for coal in the proper places, and tell those who seek for it in the numerous other situations where it has been sought, that they are only throwing away time, labour, and money.
This highly interesting subject cannot, perhaps, be better concluded than in the words of that eminent geologist and talented writer, the Rev. Dr. Buckland, who, in his Bridgewater Treatise on Geology &c, has the following striking and beautiful passage:--
"Few persons are aware of the remote and wonderful events in the economy of our Planet, and of the complicated applications of human industry and science, which are involved in the production of Coal that supplies with fuel the Metropolis of England. The most early stage to which we can carry back its origin, was among the swamps and forests of the primeval earth, where it flourished in the form of gigantic Calamites, and Stately Lepidodendra and Sigillariae. From their native bed, these plants were torn away by the storms and inundations of a hot and humid climate, and transported into some adjacent Lake or Estuary, or Sea. Here they floated on the waters, until they sank saturated to the bottom, and being buried in the detritus of adjacent lands, became transferred to a new estate among the members of the mineral kingdom. A long interment followed, during which a course of chemical changes and new combinations of their vegetable elements have converted them to the mineral condition of Coal."
"By the elevating force of subterranean fires, these beds of coal have been uplifted from beneath the waters to a new position in the hills, and mountains, where they are accessible to the industry of man. From this fourth stage in its adventures, our coal has again been moved by the labours of the miner, assisted by the arts and sciences that have co-operated to produce the Steam-Engine, and the Safety-Lamp. Returned once more to the light of day, and a second time committed to the waters, it has by the aid of navigation been conveyed to the scene of its next and most considerable change by fire; --a change during which it becomes subservient to the most important wants and conveniences of man. In this seventh stage of its long eventful history, it seems to the vulgar eye to undergo annihilation; its elements are indeed released from the mineral combinations they have maintained for ages, but their apparent destruction is only the commencement of new successions of change and activity. Set free from their long imprisonment, they return to their native atmosphere, from which they were absorbed, to take place in the primeval vegetation of the earth. To-morrow they may contribute to the substance of timber, in the trees of our existing forests; and having, for a while, resumed their place in the living vegetable kingdom, may, ere long, be applied a second time to the use and benefit of man. And when decay or fire shall once more consign them to the earth, or to the atmosphere, the same elements will enter on some further department of their perpetual ministration in the economy of the material world."
Tertiary and Recent Deposits.
The Tertiary strata are characterized as an assemblage of stratified deposits, more or less consolidated, and consisting chiefly of beds of gravel, clay, incoherent sand, or friable sandstone, in which land and freshwater shells, drifted wood and lignite, with the remains of fishes and cetacea, are mingled in such a manner as to indicate their deposition in Lakes or Estuaries; and in many cases, there are such alternations of marine and fluviatile deposits, as to show that the land, during the tertiary period, was elevated and submerged more than once.
The tertiary strata are also distinguished by the large number of shells of existing species found in them, in a fossil state; the total number of distinct species yet found in them in Europe amounting to upwards of 3,000!
The strata of the tertiary and upper secondary epochs afford evidence of the slow progress by which even these comparatively modern deposits have been elaborated, and furnish us with undoubted proofs of the long lapse of ages employed in bringing the Earth into its present condition.
As the Primary rocks exhibit no traces of fossil-plants, shells, or animals, it may thence be concluded that there was a time when no living beings existed on the Earth; and from the evidences of succeeding formation, that, before the creation of man, the world was inhabited by at least three different generations of animals, which had been successively created and destroyed, or became extinct.
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It is supposed, with reason, that the creation of vegetable bodies preceded the creation of the animals that were to devour them, In those early days when the lofty Pines, the stately Palms, and the gigantic Equisatecae, waved in the primeval forests, the Earth was inhabited only by reptiles of an immense magnitude, the Megalosaurus being upwards of 70 feet in length, the Ichthyosaurus, a creature combining the trunk of an ordinary quadruped, with a neck like the body of a serpent, the head of a lizard, the teeth of a crocodile, and the paddles of a whale; and the Pterodactyle, the most extraordinary of extinct animals, uniting the characters of a bird, a bat, a reptile, and a quadruped.
In the second period, the terrestrial mammalia appear to increase in number, and we find along with them numerous Pachydermata, or animals with thick skins, and other genera of aquatic or amphibious animals, which dwelt on the margin of lakes and rivers. These, and other species varying in size from the Rhinoceros to the hog, were found by Cuvier in the fresh-water formations of Montmartre, near Paris.
In the third period lived the Mammoth, the Mastodon, the Hippopotamus, and those large sloths, the Megalatherium, and the Megalonix, the giants of the natural world, and the grandest and the last specimens of that extraordinary antediluvian population, over which man never swayed his sceptre.
The Lion and the Tiger are supposed to be the successors of the creatures last mentioned. Up to this stage, no traces of man or of his labours on Earth, can be detected, and this gives the remarkable result that the three periods above named were succeeded by a fourth, in which the Almighty placed man upon earth, and created as his subjects and servants, those races of living beings who now occupy the surface of our globe, or who inhabit the depths of our oceans.
Although hitherto no organic remains of extinct species of mammalia, or of reptiles, have been discovered either in the Islands of New Zealand, or in the continent of Australia, it by no means follows that such exuviae of former creations may not exist and be brought to light. The researches of Australian geologists lead to the inference that both New South Wales and Van Diemen's Land were above the ocean during the whole period in which the greater part of Europe was yet under water, and that they did not descend until the whole enormous mass of the European secondaries, from the new red-sandstone to the chalk, and part of the tertiaries, had been deposited, after which some portion descended and received partial accumulations of marine detritus, since which period those countries have risen again to a higher level. These phenomena give therefore enormous antiquity to the singular classes of indigenous animals and plants inhabiting Australia.
In New Ulster, tertiary strata are found covering an extensive area in the central parts of the province, but little is as yet known of the fossils found in them, and no attempt has been made either to arrange or classify them. In the neighbourhood of Auckland, which occupies nearly the centre of a tertiary basin, somewhat similar to the London and Paris basins, the cliffs forming the shores of the river Waitemata, are composed of a soft friable sandstone in horizontal strata, alternating with strata of indurated clay and ironstone, and containing in some places, the limbs and branches of trees in a semi-carbonized state, imbedded in the clay; at other places, the cliffs consist of a remarkable conglomerate or peperino in layers with seams of a substance resembling lignite.
Opposite the island of Waiheki, the coast is comparatively low, and the cliffs there also consist of a soft white sandstone in horizontal strata. This formation extends in an easterly direction nearly to the Gulf of Houraki, and westerly towards Kaipara. To the north the tertiary strata extend to Mahurangi.
With respect to the original formation of a large portion of the primary, secondary, and tertiary strata of New Ulster, the following would appear to have been the process. A series of submarine volcanic movements first gave rise to numerous small islets and rocks, similar to those which may now be seen on many parts of the coast. These islets and rocks would consist partly of those crystalline mineral masses to which it has been usual to assign the name of primary, and partly of the subjacent strata which constituted the original bed of the ocean. Subsequent elevatory movements would then form larger islands by the junction and uniting of those first raised; and at length by the continued rising of different parts of the bed of the ocean, a number of basins would be formed, each having its system of rivers, together with disconnected gulfs, which would receive the drainage of those basins.
Some of the groups of islands which had first arisen, would in the course of time become the principal mountain ranges of the island; for, as in Chili, a single earthquake has raised permanently the coast for 100 miles in length, to the average height of 3 feet, --so, a repetition of 1000 shocks, of equal violence, would produce a mountain chain 100 miles in length, and 3000 feet in height.
Finally, volcanic eruptions would take place in the centre of these tertiary basins, and we should then have the general character and appearances presented to us in
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many parts of New Ulster, where are to be seen numerous conical hills and craters of eruption, piercing through strata of argillaceous deposits and sandstone of the tertiary epochs.
With regard to the fluviatile and marine deposits, now in progress, forming deltas, islands, and shoal-banks, which modern deposits are usually included under the general name of "Alluvium," these are to be found at the mouths of most of the rivers and estuaries of New Ulster, as at Hokianga, Kaipara, and Manukau, where they form bars and banks of sand, extending in some places, several miles seaward, and obstructing the navigation of those rivers, which would otherwise possess great commercial advantages. Of this class also, are the deposits now forming at the head of most of the estuaries in the Province, some of which are rapidly filling up with these sedimentary deposits.
The estuary of the Thames is an instance of this process; an extensive bank of mud and silt stretches off the mouth of the rivers Thames and Piako, and is constantly receiving fresh accessions of sedimentary matter. The velocity of the tide is accelerated in its advance up this estuary, by the narrower bounds into which a large body of water is forced to flow, and during the ebb-tide, the sediment held in suspension in the waters of the two rivers, is carried to such a distance from their mouths that very little of it returns up the rivers with the next tide:-- thus a large portion is deposited at the head of the estuary, in still water, and local accumulations form shoal-banks at the mouths of the rivers. A portion of this sediment is also conveyed by currents, and widely diffused over different parts of the estuary, and this slowly subsiding, covers its bottom with a mass of finely comminuted silty matter, unmixed with sand or gravel.
The rich and extensive alluvial plain comprised in the valley of the Thames, has unquestionably, been formed in this manner. The breadth of this alluvial flat varies from two to three miles, by a length of nearly sixty miles; at its head, however, the breadth is considerably reduced. This plain, the greater portion of which is not elevated more than six feet above the level of high water, is bounded by hills or cliffs, varying from 300 to 500 feet in height on the west, and by the river Thames on its eastern side, the river Piako flowing through the same alluvial tract, and nearly parallel with the Thames. The western hills or bluffs point out the former boundaries of the estuary, whose waters, undoubtedly, at a former period, extended to a considerably further distance inland, and that, in fact, the whole of the lower portion of the valley of the Thames has been silted up within a comparatively recent period of time.
Of Metalliferous Deposits, Mineral Veins, &c.
An acquaintance with the general results collected and classified by Geology, must be our first guide in the investigation of metalliferous and mineral deposits. This enables the observer to judge whether any particular district should, from the nature and arrangement of its rocks, be susceptible of including within it any workable metalliferous deposits. It indicates also to a certain extent, what mineral substances may probably be met with, and in what particular locality such substances will probably be found.
Positive indications of the presence of metallic ores, are some of them proximate, and others remote:-- the proximate, are an efflorescence, so to speak, of the subjacent metallic masses, particularly of copper, which is frequently found forming a green metallic coating on the surface of certain rocks. The remote indications consist in the geological age and nature of the rocks, the frequent occurrence of fragments of particular ores, or the neighbourhood of some known locality of an ore; and if in granite, or in argillaceous schistus a vein of white stone or spar is found running in a direction from east to west, there is much probability, that in some part of its depth, it may afford some useful metal. And further, if veins of spar or quartz occur in certain rocks, such veins being partly hollow and partly filled with a yellowish ferruginous substance, which in Cornwall is termed "gossan," there is every probability that such veins will be productive, and the larger the quantity of gossan found in such veins, the better is the indication usually considered.
Negative indications are derived from that peculiar geological constitution, which, from experience, or general principles, excludes certain metallic or mineral substances. Thus, the metals whether native or mineralized in the state of ore, seldom or never occur in rocks of tertiary formation, such as soft white sandstone, or soft argillaceous schist, although they may be looked for in hard schist, and in compact limestone of the secondary epoch. They may also be sought after with greater chance of success in gneiss, mica-slate, clay-slate, &c., than in serpentine, syenite, bituminous slate or basalt, and as a general rule, it may be said that volcanic territories never afford any metallic ores worth the working. It is however very common that granite includes within it workable veins of copper, silver, and lead, and tin is almost exclusively worked in the interior of granitic rocks. Respecting this rock, however, it is not generally considered, by miners, a favourable rock for copper, except it be in connexion with slate; for although in certain Cornish
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mines, copper has been plentifully obtained in granite, it has always been at no considerable distance from its junction with the clay-slate. Rich veins of lead, sometimes argentiferous, have at times been found in rocks of compact limestone, and the Sulphate of Barytes, and Fluor-spar are pretty certain indications of metalliferous deposits.
It is well known that there is often much connexion between given rocks in particular districts, and the productive mines in them; some rocks being considered more "kindly" as the Cornish miners term it, than others. The Consolidated Mines, near to Redruth, in Cornwall, offer an excellent illustration of the geological position of one of the most productive mines in that county, which are situated at or near to the junction of the granite and the clay-slate. At the western extremity of these mines, the mass of granite which forms the prominent hill of Carn Marth, dips below the surface at an angle of about 30 degrees, and is overlaid by the metalliferous clay-slate or "killas," which is itself traversed by the porphyritic rock called "elvan." All these rocks are intersected by mineral veins or lodes, which are highly productive of copper and tin, but chiefly of the former. The lodes have a direction nearly east and west, with a dip or underlie to the north, and are intersected at right angles in several places by barren veins, locally termed "cross-courses," chiefly filled with quartz, and clayey matter. The chief produce is the sulphuret of copper, called yellow copper-ore, from which the great bulk of that metal is in most parts of the world, obtained.
The metalliferous veins of Cornwall generally run in an east and west direction, although this is not invariably the case. Their dip or underlie is usually to the north. Other veins that rarely contain any metallic substances, frequently cross the metalliferous veins at right angles, or very nearly so, and are thence called "cross-courses." Their direction is commonly north and south, or within a few points, and their width varies from 2 feet to 10 feet; but whatever may be their width, they always divide tin or copper veins, and frequently alter their course, or in the language of the miners, "heave them out." These north and south veins are usually filled with quartz, or a whitish clayey substance, or a hard porphyritic rock; in the latter case, it is called an "elvan-course." The length of no one vein in Cornwall has as yet been satisfactorily proved; some of them have been traced for 4, 5, and even 6 and 7 miles, and no instance has occurred in which the bottom of a vein has been seen.
The metalliferous veins of New Ulster appear to follow nearly the same laws which regulate their types in England, and to range generally in an east and west direction, although this direction may not be maintained uniformly throughout, being subject apparently to frequent deviations from this course, which can therefore only be termed their general direction. The rocks in which these veins occur, have frequently much resemblance to the rocks which are the enclosing stratum of copper and other veins in Cornwall and elsewhere. Thus in the vicinity of Cape Colville, we find most, if not all the rocks which are productive of copper and other metals in Cornwall. For instance, we find there the primary clay-slate, or "killas" reposing on a mass of granite at an angle of from 30 to 40 degrees, and we find cross-courses of the porphyritic rock called "elvan" traversing the clay-slate, we also find veins of quartz, and lastly, we find, at several places, "lodes" or veins, which, on being examined, prove to be metalliferous, and inclose the ores of copper, lead and iron.
In 1845, whilst exploring this part of the coast, the writer discovered several well defined lodes in the clay-slate, at no considerable distance from its junction with the granite, these lodes having a general direction of nearly east and west. Positive indications of the existence of copper at this locality, are seen by the metallic efflorescence covering some of the adjacent rocks, and by the presence of the yellow and grey sulphurets of copper lining the sides or walls of the lodes. It seems probable that other metals exist in the neighbourhood, and from the limited and partial examination of the district by the writer, it may be concluded that the range extending from Cape Colville to the mouth of the river Thames, is at many points highly metalliferous, and will no doubt at some future day, prove the great mining district of New Ulster.
The only metalliferous veins which have hitherto been opened and worked in the Province, occur at the Great Barrier Island, and at the Island of Kawau; in the former the veins occur at a point near the northern extremity of the island in a hard granitic or porphyritic rock, and the ore, consisting chiefly of the yellow sulphuret of copper is intermixed with the gangue or matrix in small veins or threads. These veinstones also contain other minerals, and the ore appears to become richer in proportion to the depth at which it is worked. Hitherto, however, the workings have not been extended to a great distance, but there appears every probability that as the mine becomes better opened out, and the sinking of a main shaft, with proper adits, proceeded with, the returns of ore will become of a more remunerative description; some of the prepared samples of this mine having already commanded a high price in the English market. The ore from the Kawau copper mine is of a different description from that
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found at the Great Barrier, the geological formation of this island being of a very different character. At the Kawau, the ore is much impregnated with sulphur, containing probably on an average, not less than 30 per cent of this mineral. This circumstance has rendered expedient the erection of furnaces for the purpose of roasting or calcining the ore, which by this means is deprived of its sulphur, and reduced to a copper regulus of from 20 to 25 per cent. The advantage of this partial smelting on the spot is obvious, as it is evident that there must be in every mine, a large proportion of the poorer description of ore, which will not pay to export to England or elsewhere, but which by a cheap and expeditious process of reducing to a regulus on the spot, can thus be rendered a profitable article of export.
The writer will now conclude these desultory remarks on the Geology of the Province, by expressing a hope that the developement of the mineral resources of the Province, may by inviting the application of capital, create a permanent article of export, now much wanted, and thus contribute to place the Colony on a basis of solid commercial prosperity.
MINERALS AND METALS.
The following list, which no doubt will receive numerous and important additions, at a future and not distant period, comprises most of the useful minerals and metals, occurring in the Province of New Ulster.
Coal. --Found on the banks of the river Waikato, at a place called Kaito-tihe, between the Church Mission Station Tihoro, and the confluence of the rivers Waipa and Waikato.
Found also in the river Mokau, on the banks of the river, about 30 miles from its mouth.
Also near the North Cape, at Parenga-renga.
The specimens from the Waikato do not appear to contain much bitumen, being more difficultly inflammable than the ordinary bituminous coal. This, however, may be partly owing to the specimens being taken near the surface. When once ignited, however, they burn with a strong and durable heat, and leave a solid cinder. This coal will no doubt prove a valuable fuel for limekilns, malt-kilns, iron-founderies, and the like, as it does not appear to contain much sulphur. It would no doubt also prove a good coking-coal, and with the judicious application of a current of air, and in a properly-constructed furnace, would no doubt prove a good steam coal.
Copper. --Found at the Great Barrier Island, at its northern and southern extremities.
Found also on the coast, near to Cape Colville, in the primary range extending thence to the mouth of the river Thames.
Also at the Island of Kawau, on the west side.
Also on the coast near to Mongonui; Doubtless Bay.
The ore mostly found at these different localities, is the yellow copper pyrites, or yellow copper-ore, from which the great bulk of this metal is, in most parts of the world, extracted. Certain varieties exhibit beautiful iridescent colours, being the "peacock" copper ore. At the Kawau the ore is much impregnated with sulphur; it also [contains a large proportion of iron. Some fine samples of the black oxide of copper have been obtained from this mine, and small quantities of native copper.
Iron. --Found abundantly in the form of pyrites, or sulphuret of iron, in many localities, and in rocks of all ages. In the form of iron sand (titanitic iron? fer magnetique sabloneux), it is found at the mouths of most of the rivers on the west coast, particularly at Taranaki. This variety furnishes generally the best of bar-iron and steel. The Swedish iron is mostly extracted from iron-sand.
Lead. --Found on the coast in veins in the mountainous range extending from Cape Colville to the mouth of the Thames, in the form of galena, or sulphuret of lead. It seems highly probable that some specimens from this locality are argentiferous; but whether the silver exists in sufficient quantity to repay the cost of extraction, ia doubtful.
Manganese. --Found abundantly at the Island of Waiheke, in the form of the oxide, or black manganese ore; also a variety (carbonate of manganese) of a red colour; and a silicate of manganese, or manganese-spar. Earthy manganese, or black "wad" considered a hydrate of manganese, is also a common mineral.
Limestone. --Found at Kawhia, on the south side of the harbour, and on the left bank of the Awaroa, where it occurs in cliffs and masses; and in the form of stalactitic carbonate of lime. Found also in the bay of Tauranga, in horizontal strata, on the sides of the hills, in slabs about an inch thick. Found also at Wangarei, in beds of an impure description; also, about two miles from Wangaroa harbour, a carbonate of lime, or marble is found, of a red and variegated colour, in connection with chloritic and argillaceous slate. This marble is stated by Dieffenbach to be of a fine close grain, and to exist in sufficient quantity to become of importance for domestic architecture at some future period.
Slate. --Found in one of the upper tributaries of the Hokianga estuary, the Mangamuka, where there is said to be an exten-
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sive quarry of a lightish blue colour. It projects into the river, presenting a rugged surface, from exposure to the weather. It readily splits up into large thin slates or slabs; the strata dip downwards at an angle perhaps of 65 degrees, to the north, and exhibit every appearance of a fine description of slate.
Clays. -- Of various kinds, suitable for bricks, tiles, and pottery-ware, are found extensively disseminated in the tertiary strata of the Province. Of these some are infusible, and others fusible: the infusible clays being Aluminite, Colyrite, Kaolin, Cimolite, Plastic-clay and Lithomarge; and the fusible being Fuller's-Earth, Figuline, adhesive or slaty clay and some others.
Sulphur. -- This mineral substance is found at White Island, in mass intermixed with sand, &c.; being the produce of the Solfatara. It requires however to be purified, either by melting or by sublimation, before being applicable to commercial or industrial purposes. The means are here afforded for the manufacture in the Province of a cheap sulphuric acid, an article of great use in the arts, and which has hitherto been a very expensive article of import, owing to the danger to be apprehended from it, and consequent dislike of shipowners to allow it to form part of their cargo. The manufacture of coarse sulphuric acid, is very simple and the apparatus inexpensive.
Building Stones. --Granite is found in large masses near Cape Colville, and at the Barrier Island, of different colours and degrees of fineness. Freestone of good quality, fit for constructing bridges, piers, &c, is found at Mercury Bay, adjacent to the anchorage. A calcareo-siliceous sandstone is also found at Matakana; this stone is soft when first quarried, but becomes harder by exposure to the weather.
The following brief summary of recent geological discoveries in Australia, whilst pointing to a wide spread field of mineral wealth, in that extraordinary country, the partial development of which has already elevated it from the rank of a secondary Colony to one of first rank and importance, and which will no doubt in the present generation cause it to take its place among the Nations of the earth, shows also that it is to scientific exploration, rather than to accident, that the discovery of her mineral treasures ought to be ascribed.
The gold discoveries of Australia, so startling to the colonists, were not new to the scientific world. Nearly three years ago, in an "Essay on the Distribution of Gold ore," read before the British Association in 1849, Sir Roderick Murchison reminded his geological auditors "that, in considering the composition of the chief, or eastern ridge of Australia, and its direction from North to South, he had foretold, (as well as Colonel Helmerson, of the Russian Imperial Mines,) that gold would be found in it, and he stated that, in the course of the year 1848, one gentleman resident in Sydney, who had read what he had written and spoken on this point, had sent him specimens of gold ore found in the Blue Mountains; whilst from another source he had learnt that the parallel North and South ridge in the Adelaide region, which had yielded so much copper, had also given undoubted signs of the presence of gold. The operation of English laws, by which noble metals lapse to the Crown, had induced Sir Roderick Murchison to represent to Her Majesty's Secretary of State, that no colonists would bestir themselves in gold-mining, if some clear declaration on the subject were not made, but as no measures on the subject seemed to be in contemplation, he inferred that the Government might be of opinion that the discovery of any notable quantity of gold might derange the stability and regular industry of a great colony."
Such was the language used by Sir Roderick Murchison in 1849, and in 1851, the colony was startled by the fact which brought emphatic confirmation to his prophecy.
So far back as 1841, the Rev. W. B. Clarke knew by personal discovery that gold existed in a particular region of Australia, and, reasoning from analogy, surmised that gold would be found to exist in other similar regions, where the same indications occurred. To use his own words, -- "In all the islands surrounding Australia, we have a phenomenon well known to geologists, viz., the junction of certain sedimentary formations with igneous rocks of a certain class, the planes of contact being marked by the effect of transmuting influences, by disruption, derangement, and the development of metalliferous products. 'Similis simili gaudet.' We may look for gold in all of them."
The Count Streleski, also in a Report on the Economical Mineralogy and Geognosy of a portion of New South Wales, which he explored in 1840, and which Report was published in 1841, by order of the House of Commons, named amongst other ores found by him, "an auriferous sulphuret of iron, yielding a small quantity of gold, found in Siberia locality, Vale of Clywd, South Cox's river."
These facts are mentioned, not to detract from the just claims of the practical discoverer of these golden treasures, (Mr. Hargreaves,) but to draw attention to the former laborious explorations of Australian geologists, particularly Sir Thomas Mitchell, Rev. W. B. Clarke, and Count Streleski, and but for whose labours it is probable that the
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rich regions of Australia might have remained in obscurity.
In an addendum to a report of Sir Thomas Mitchell recently published, on the gold fields of Wellington and Bathurst, in addition to his account of the detailed survey which he had made in those counties, he particularized other localities where auriferous rocks had been seen by himself during his several former surveys and explorations. He commences his addendum by stating that although he has closed his longitudinal section westward from the present diggings to the granite of the Curumbenya range, and eastward to the granite of Bathurst, that dykes of quartz and chlorite schist intercept the waters of the Kalingalungaguy, (a native name signifying "white stones stopping the water"): that hills of mica schist and quartz were mentioned as having been seen by him when in search of Mr. Cunningham."
Sir Thomas further observes, that the geological structure lower down the Lachlan seems to be of the most auriferous character; and, in the 2nd volume of his work, he thus describes the dyke extending from the LachIan to Hurd's Peak of Oxley, "Tolgo" of the natives. "A low ridge of quartz extends from the Goobung to this peak, the base of which consists of chlorite slate, and its summit of squarish pebbles of quartz, with the angles rounded, associated with fragments of chlorite slate. The ridge of Kalingalungaguy consists of quartz, clay-slate, and ferruginous sandstone, but I observed in the bed of the river a trap dyke, extending to the Balloon ridge. Of the few low hills about the Lachlan, it may be observed that they generally range in lines crossing the bed of that river, in a nearly North and South direction." (Page 31.)
The following passage also merits particular attention:-- "The vast field which Australia thus presents of such auriferous rocks, may be better conceived when I mention what I saw of it in passing through Australia Felix in 1836. On the 10th of July, beyond the Avoca, I found the same ferruginous conglomerate so often mentioned, with the strike in the usual direction (north-north-west), and hills beyond it, consisting chiefly of quartz rock. The character of the granite upon the Glenelg seems to me to indicate the near vicinity of metallic rocks, but in the country traversed by my party on its return, I still remember to have seen more of the schistose or metalliferous rocks than I had in all my life before. The trappean conglomerate with imbedded quartz pebbles, on the flanks of the granite range of Mount Cole, ought to guide modern prospecting parties to the localities where gold may be found, and also the description of the country, from thence eastward as passed by my party. The banks of the Colibaw, in particular, seemed the most favourable from what I have lately learnt, for the development of gold:-- strata of clay-slate inclined almost perpendicularly to the horizon, projected at parts of the left bank, and over this clay-slate I found trap-rock." -- Colibaw, we may state, is the Forest-creek of Victoria, and Mount Alexander is no other than the Mount Byng, laid down by Sir Thomas Mitchell in his general map of New South Wales, and described by him, in 1836, as a locale of highly auriferous character. His predictions also with reference to Mount Cole, seem likely to be verified. In the "Geelong Advertiser," of March 15th ult., is the following paragraph:-- "Portland, another new gold field. Mr. Bilston has found one of the most handsome specimens of gold which we have yet seen; the locality in which it was discovered is Mount Cole; from two or three spadesful of earth, he obtained the sample, which he has shewn to many parties in town, and there is but one opinion regarding it, that it is even purer than either Mount Alexander or Ballarat gold. It may be said that this field has been discovered accidentally."
How much accident has had to do with this discovery, we shall not now stop to enquire; the above extracts from works published upwards of twelve years ago, ought to show that for the survey of that rich region, the colonists of Victoria have to be grateful to New South Wales; and that to science rather than accident, ought the discovery of these golden treasures to be ascribed.
In the 'Sydney Morning Herald' of May 1st ult., we are also informed that the Rev. W. B. Clarke has reported to the Government the existence of a tract of country along the Bendoc and Delegate rivers, which he has very carefully and elaborately examined, and over which he has found gold to exist in nearly equable distribution. He has offered no positive opinion as to the value of this tract, which covers more than 400 square miles in extent! But he states that he has found gold not only along the rivers, but on the ranges, and in almost all kinds of localities. A spade can hardly be used in some parts without bringing up the precious metal. In the prospecting-pan it is no unusual occurrence to find from 40 to 250 particles. The country is all slate and quartz, or granite. As the Bendoc and Delegate rivers rise in enormous swamps, it is not unlikely that at the heads (which are, it must be mentioned, very difficult of access) there is abundance of gold. Whether future investigation prove that this field is, or is not valuable in a commercial point of view, still the fact is astonishing, that gold in such a way should be distributed over so large an area. The persons who have been prospecting confirm Mr. Clarke's report; and from them and him, it is found that the
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general proportion of product is in the few places tried, from half a grain to a grain of gold per bucket, which at 240 buckets a day, will realise to the washers half an ounce per diem.
As the rivers are always flowing, and as they run in valleys filled with alluvial soil, if the isthmuses could be drained, and this would be easy, it is believed that a greater yield would be realized. The extent of the gold area is believed even to be greater than that above named. The weight of the largest piece in Mr. Clarke's possession is stated to be 15 or 16 grains. If the field eventually prove of small commercial importance, still it is satisfactory to know that no pains have been spared to ascertain its probable value. The distance from Sydney to the boundary line of the colony, which intersects this field, is, where it crosses the rivers in question, from 330 to 340 miles. Mr. Clarke's report on this district is said to be very minute in description and details.
ADDENDUM TO GEOLOGICAL SKETCHES.
Prospects of Gold-finding, and hints to Gold-seekers in New Zealand.
The conditions or "constants" under which gold is usually discovered in Europe, Africa, America, and Australia, are now so well known, that it is possible to predict, with tolerable certainty, what countries, from their geological formation, and mineral characteristics, are likely to be added to the list of auriferous regions.
A few centuries ago, it was thought that gold was a production only of the hottest countries. Columbus, when sailing along the coast of Cuba, wrote in his journal:-- "To judge from the great heat, this country must be rich in gold." A similar groundless belief, respecting the climate prolific of diamonds, is maintained in some publications even of our own day. Nevertheless, diamonds, and still more abundantly gold, are now found in the Uralian Mountains, under the 65th degree of north latitude, and the Siberian gold-mines, situated on the slopes of the northern branches of the Altai Mountains are daily disclosing new treasures.
In Australia, the gold alluvia appear to spread over a vast extent of territory, and we learn from Sir Thomas Mitchell that the auriferous formations chiefly traversed by him were a trappean conglomerate with embedded quartz pebbles, on the flanks of granitic ranges, and strata of clay-slate inclined almost perpendicularly to the horizon, and over this clay-slate, trap-rock. The presence of a ferruginous sandstone or conglomerate, with hills of quartz rock in the vicinity, appears to be considered by Sir Thomas as a favourable indication of the near vicinity of metallic and auriferous rocks; where, also alluvium and detritus of quartz rocks abound, in the neighbourhood of veins or dykes of quartz, there gold may be expected to be found, but this indication is by no means a positive one, as it is certain that quartz may be found in abundance in various localities, without being accompanied by gold.
Collecting then the data derived from the experience of Australia and other auriferous countries, it appears that the mineral formations in which this metal chiefly occurs, are the crystalline primitive rocks, the compact transition rocks, the trachytic and trappean rocks, and alluvial grounds. In Australia, gold is much more commonly found in the alluvial grounds, than among the primitive and pyrogenous rocks just described; it is there found disseminated in the form of spangles and fine dust, in the silicious, argillaceous and ferruginous sands of certain creeks and rivers, or in the surface soil and gravel adjacent to these streams, and sometimes even in the clay, beneath the gravel, &c. The following extract, from the 'Geelong Advertiser,' proves this singular geological fact:-- "The earth of Ballarat is a teeming store of riches, which the explorers have barely entered; many spots were abandoned as exhausted, when cleared of the black surface soil and gravel, the clay being declared unproductive. But now the whole system of operation is changed:-- the surface soil is thrown aside, the gravel is heaped upon it, the clay is flung aside, (the first seam) the quartz is then penetrated, and from six to seven and even ten feet deep, men are delving to reach the 'Eldorado' of the purple clay, superimposed upon a white clay formation, which rich vein is now proved to extend nearly half a mile, and most probably through the whole of the range. Should this supposition be correct, and it is founded so far on actual observation and experience, there will be room for tens of thousands, and a yield unparalleled."
It appears that in these veins of blue or purple clay, the gold is clearly perceptible, and lying disseminated in it in such profusion and size, as to be easily picked out with the point of a knife. One tin dishful of this rich deposit has been known to yield from six to eight ounces of pure gold!
Gold, if it is to be found at all in New Zealand, must be sought under the one or the other of the three following conditions, that seem to identify it in all other countries. These conditions are,
1st. The diluvial deposits, found in the beds of streams and valleys, and occasionally, where obstructions have occurred, to a limited extent on the higher lands in the neighbourhood of rivers, embedded in gravel, and the debris of rocks, and continuous as regards the quality of the gold, and fre-
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quently as regards the given contents per cubic fathom.
2nd. In veins and beds which are generally found to exist in mountains of secondary height, but parallel to the meridional range of the country. The minerals composing the veins are either quartz, calcareous spar, or sulphate of baryta. The ores that accompany the gold in these veins are chiefly iron pyrites, copper pyrites, galena, blende and mispickel.
3rd. In alluvial grounds, in the beds of rivers, and in the soil of the adjacent plains, the soil of these plains containing, at a certain depth, gold in spangles and grains; separable by washing. In the neighbourhood of auriferous veins, these alluvial deposits are frequently very rich, and in some cases, have led to the discovery of important mines, as the once-famed Gongo Soco gold mine of Brazil.
An important circumstance in connexion with these alluvial deposits, is that the productiveness of the deposits of the valleys gradually diminishes as the acclivity of the hill increases, and thus plainly shows the origin of these deposits. It has generally been found that, at a distance from the mountains in which the auriferous streams rise, there is a point in which the gold is found in nearly an impalpable dust; that going up the stream, it insensibly increases in coarseness, and in laminated particles, until the gold is found with its natural roughness and points, as if fresh broken from its matrix. Larger pieces sometimes occur, even to several pounds in weight, as also pieces are found containing portions of the matrix, thus occasionally enabling the "prospector" to form a shrewd guess of the neighbourhood in which to look for a rich mine, with some hope of success. A great mistake is however frequently made in gold districts upon finding a rich spot:--the whole area of the country is supposed to be equally rich; of course time soon shows the fallacy of this belief.
As we have in New Zealand many of the conditions under which gold is found in other countries, as well as most of the gold-bearing rocks; such as crystalline rocks composed of quartz and felspar, with a grey base, sometimes approaching to the character of porphyry; together with dykes of quartz in talc and mica-slate schist, &c; also sienitic and granitic rocks, frequently schorlaceous, the schorl in the granite being often seen in black strings, in crystals, or in rhomboidal particles; with chlorite slate, hornblende rock, porphyry, protogine, basalt, greenstone, ancient sandstones, shales and conglomerates; all of these rocks being more or less favorable to the development of the metals, it seems by no means improbable that gold may, at some future day, be added to the list of metals already known to exist in the Province of New Ulster.