The Geology of the Region about Preservation and Chalky Inlets, South-west Fiordland, New Zealand.
Historical Introduction, Summary of General Geology and Detailed Account of The Unfossiliferous Sediments, Igneous Rocks and Tectonics.
[Read before the Otago Institute, 12th July, 1932; received by Editor, 8th October, 1932; issued separately, October, 1933.]
Fossiliferous Ordovician Rocks.
Intrusive Plutonic Rocks.
Metamorphism of the Lower Ordovician Rocks.
Long Sound Series (? Upper Ordovician) and its Tectonics.
Quartz-Veins, Minor Basic Intrusions, etc.
Preliminary Account of Lower Ordovician Stratigraphy and Faunal Succession.
Unfossiliferous and Metamorphic Ordovician Rocks.
The Long Sound Series.
The Intrusive Rocks.
Bald Peaks-Treble Mt. Massif.
Great Island-Kakapo Range Massif.
Long Sound Massif.
The Norite of Long Sound and Other Basic Intrusions.
Intensity and direction of folding.
Easterly-directed Fault Thrusts.
Fault and Fracture-Systems.
Faults, fractures, and joint-planes trending nearly east and west.
Faults, fractures, and joint-planes trending approximately north-east.
Faults, fractures, and joint-planes trending west of north.
East-south-east and other fractures.
The Tertiary Rocks.
Structure and Dislocation of the Tertiary Beds.
List of Illustrations.
The region to be described lies in the extreme south-west of New Zealand. It first came under the notice of Europeans on March 25, 1773, when Captain Cook, approaching New Zealand on his second great voyage, sighted the white cliffs of Chalky Island, but, as the coastline was “wholly obscured by a thick haze,” stood out to sea again, and reached his objective, Dusky Sound, on the following day. Thirty years later sealing vessels began to frequent the coast, and its main features became known especially to a band of American sealers landed by the “General Gates,” who, after seventeen months of misadventure near Preservation Inlet, were rescued in November, 1822, by a Sydney exploring schooner in charge of Edwardson, by whom a general examination was made of the recesses of Chalky Inlet. His results were communicated to M. de Blosseville, midshipman on a French exploring vessel, who published in 1826 a comprehensive account of the region, together with a map on which appear some of the present names for the salient features.*
The detailed survey of the coastline was made in 1849–51 under Captain Stokes of the H.M.S. Acheron, the surgeon of which vessel made the first geological examination of the region (C. Forbes, 1855). The occurrence of pink granites forming the ranges, flanked by meta-morphic and steeply dipping “dark blue trap with a slaty fracture” forming the islands in Preservation Inlet, and underlying the coal-bearing sandstones and grits on Coal Island, was noted by this observer, and details were given concerning the occurrence and character of the coal. The origin of the “rift-like harbours” or sounds northwards from here is referred to the cracking of the crust consequent on the elevation of a ridge along an axis running some distance inland from the west coast, while to the presence of a parallel ridge adjacent to the coast is ascribed the origin of the thresholds at the mouths of these deep sounds.
Further studies were made in June and July of 1863 by Hector, who noted the main geological formations, indicating their general distribution on his manuscript map of Otago (1864) which is preserved in the Geological Museum of Otago University, and in which (a) contorted and foliated schists, (b) granite, and (c) brown coal formations are the three categories concerned. He paid special attention to the coal seams at Coal Island and Gulches Head, but was unable to land on Cavern Head, where later in the same year the first gold-bearing reef was discovered (fide McKay, 1896). Hector's account is, however, noteworthy as being the first statement of the production of hanging valleys as the result of glaciation, the
[Footnote] * Most of these were doubtless supplied by his informants, but three of purely French origin were probably proposed by himself. Two, Presqu'île le Chevalier (now C. Providence) and Presqu'île Bréauté (the Treble Mountain Peninsula) have not survived, but the name Point Puysegur may perhaps have been used in honour of the French navigator A.-H.-A. de Puységur (1752–1809), though no explanation was given by de Blosseville. Edwardson was keenly interested in the birds of the district, and de Blosseville's name Bras Canaris may recall the abundance of such songsters. The name Cunaris used on the Admiralty chart for the same feature would thus appear to have been derived by an error in transcription.
effects of which were recognised around the region herein discussed. Observations tending to indicate coastal depression and others indicating coastal elevation were also recorded.
Hutton visited the region ten years later, and gave (Hutton, 1875) a rather more precise account of its features. He recognised the occurrence in a neighbouring region of gneisses and mica schist which he classed as the Manapouri Series of presumably Archaean age. The argillites and clay slates noted by him were referred to an early Palaeozoic Kaikoura Series, and it was remarked that the granite sharply invaded these, producing but small contact meta-morphism, whence it was inferred that the intrusion of the granite was definitely later than the formation of the Kaikoura sediments, and was much later than, and in no way connected with, the dynamic metamorphism of the rocks of the Manapouri Series. Contact-specimens of slate and granite collected by him were described and analysed by Liversidge (1877–1884). Hutton gave additional details concerning the coal measures, inferring their Tertiary age in the absence of fossils from the resinous character of the coal. Confirmation was adduced for the former glaciation of the region by noting the abundance of granite erratics in areas of Palaeozoic and Tertiary rock. Hector's deductions as to the subsidence of the region were held to be unconvincing, but additional evidence was found for regional uplift in the extensive series of terraces extending for many miles eastward from Puysegur Point. In 1889 Hutton described (as syenites) two granite erratics from Kisbee Beach, and his petro-graphical notes upon the rocks of the area have been briefly amended and extended by Hutton (1899), Marshall (1907), and Speight (1910).
In 1887 Reischek explored the north-western portion of this region, i.e., that lying between Northport and Dusky Sound, discovered several lakes and described other topographic features. An attempt made late in the “eighties” to settle a Scottish fishing community at Cromarty in Preservation Inlet proved unsuccessful, but in 1889 alluvial gold was found for the first time in exploitable amount on Coal Island, the region was surveyed trigonometrically (Johnstone, 1889), and a small “rush” set in, the working of the alluvium leading to the discovery of small reefs on Crayfish Island and larger ore bodies at the “Morning Star” Claim, near Long Beach or “Te Oneroa,” at the “Golden Site” on Wilson River, and at Sealers' Creek, while a complex gold-, silver-, lead-, and copper-bearing reef occurring in granite was developed on Isthmus Sound. It is stated that in 1890 five hundred miners were on the field, and two hundred were there at the time of the visit of the Government Mining Inspector (Gordon, 1893). For a short time, it is said, about two thousand ounces of gold were obtained per month. This activity was, however, of short duration, and gloomy reports were soon current. A more optimistic view was, however, held by Carrick, who spent sixteen weeks exploring the region, reports of gold occurring in the neighbourhood of Cunaris Sound and of the head of Edwardson Sound being made by him. An abstract of his reports and a
copy of his sketch map of the region were published by the Department of Mines (Gordon, 1895). By 1896, however, scarcely forty miners remained in the district. The “Golden Site” had lost its lode, and the “Morning Star” was in difficulties (McKay, 1896). A small amount of mining continued spasmodically for nearly twenty years more (see Inspecting Engineer's Reports, 1893–1913). In 1930 only one prospector remained, with the exception of the staff of the Puysegur Point lighthouse, the sole inhabitant of the region. The old workings are in ruins and all tracks are overgrown.
A detailed investigation of the geology and topography of the region was made by McKay in January-April, 1896, who gave most attention to the area eastward from Preservation Inlet to Big River, and examined the shores of Preservation and Chalky Inlets more cursorily. With the latter, therefore, the present investigations are particularly concerned. McKay followed Hutton in assuming the Archaean age of the metamorphic rocks north-east of the granite belt. On the west side of this he found “Lower Silurian” graptolites in two places among the graphitic argillites and sandstones in which the auriferous reefs were situated, but apparently brought back no specimens of these fossils. He also noted that the upper members of the Tertiary coal-bearing series were marly shales which, a short distance south-east from Puysegur Point, contained fossiliferous concretions with large specimens of Ostrea. He found also that locally auriferous glacial deposits extend over the plateau areas which slope regularly from a height of about 1000 feet down to the coastal cliffs on the mainland and on Coal Island, and held that they had been resorted by wave action and that the coastline had been elevated to the present height, this post-glacial movement having been followed by the deep dissection of the moraine-covered platform. Small locally-developed auriferous beaches raised to a height of 50 feet indicate the last phase of this elevatory movement. A systematic account of the topography and the former extent of the glaciers was also given.
In 1903 Andrews studied the physiography of the West Coast Sounds, and his observations on the region about Preservation Inlet are scattered through a group of papers (Andrews, 1905, 1906, 1907, 1911). He held that the sounds were pre-glacial valleys cut by river action in an elevated plateau, which rises north-eastwards from its lowest elevation near Preservation Inlet. These valleys were greatly enlarged and deepened by glacial erosion, the deepening being most marked at points of constriction and convergence, while erosion was greatly diminished and the sounds consequently are shallow where they broaden and diverge, Preservation Inlet being taken as typical of this feature. Tectonic movements and subsidence, he thought, played no part in their formation. Later (with Speight, 1910) he became doubtful of the correctness of assigning to glaciation alone the responsibility for the vast enlargement of the pre-glacial valleys, and considered that these depressions in part might be tectonic. The region now under consideration was thus described by him:—
“Preservation Inlet, New Zealand. Here a long and fairly shallow inlet, dotted over with islands, runs up along its lower portion
into a plateau about 1000 feet in height, while its upper portion runs among much higher plateau remnants. The various topographies are separated by rough youthful forms. Heavy glaciers have passed down the inlet or sound, bearing moraines and other signs of ice action in various places. The most feasible explanation is that earth forces have raised a peneplain here in recent times to form two high plateaus, and dropped a centre block to form the inlet, which has since been modified by ice-erosion…. The long and profound cañons discharging into the fiords may easily be explained by erosive processes alone” (Andrews, 1911, p. 134).
A collection of graptolites made by J. S. Nicol (probably from the spoil-heap of the “Morning Star” mine) was described by Dr. T. S. Hall (1915), who recognised therein the basal Ordovician forms Clonograptus tenellus, C. tenellus var. callavei, Tetragraptus de-cipiens and Bryograptus sp., characteristic of the Lancefield series in Victoria.
In 1921 Professor Park grouped the various sedimentary formations in Fiordland into three main divisions, holding that they are disposed in parallel zones dipping south-westwards, and accordingly are of decreasing age when traced westward. These are the Dusky Sound Series of presumably pre-Cambrian intensely metamorphosed schists, to the west of which lies the less altered possibly Cambrian Maniototo Series, invaded by batholiths which separate it from the westernmost and youngest series, the Preservation Inlet Series, of Lower Ordovician argillites and greywackes. The Dusky Sound Series if a definitely pre-Ordovician Series is apparently unrepresented in the area herein discussed, but by inference it may be assumed that Professor Park would have placed the schists north-east of the granites in Long Sound at least in part in his Maniototo Series, and in part, perhaps, in his Dusky Sound Series also.
In 1922 Park announced the discovery at Cape Providence of graptolite clay-slates co-eval with those of Golden Ridge in northwest Nelson, and higher in the Lower Ordovician than those of the “Morning Star” mine. He concluded that the Ordovician rocks in this region were arranged in a series of close-packed asymmetric folds with a general westerly dip. In 1927 Keble determined eighteen species in the material collected by Professor Park, and confirmed generally his determination of their age, pointing out its equivalence to that of the C4 zone in the lower portion of the Castlemaine Series of Victoria as then understood. No indication was, however, seen of the presence of forms characteristic of the Bendigo Zone, which intervenes between the Lancefield and Castlemaine Zones of Victoria. The search for such beds was the principal object of the recent expedition.
All earlier reports thus clearly indicated Preservation Inlet as a region favourable for the search for additional graptolite-bearing strata, and for a study of the tectonics of the Ordovician rocks and their relationship to the metamorphic formations and of the geomorphology of fiords. Accordingly, with the assistance of a Government Research Grant of £150 obtained through the New Zealand Institute, an expedition was organised by the present writer wherein
geological teachers from three of the New Zealand University Colleges might co-operate with a geologist experienced in the study of Australian Ordovician rocks. Through the courtesy of the Chief Secretary of Victoria, permission to join the party was obtained for Mr. R. A. Keble, F.G.S., Palaeontologist to National Museum, Melbourne. Professor Bartrum, of Auckland University College, and Mr. L. C. King, M.Sc., F.G.S., of Victoria University College, Wellington, with the writer completed the scientific party. Special acknowledgment must be made of the unstinted helpfulness of Mr. Charles Yunge, the captain-owner of the schooner that conveyed the expedition, to whose enthusiastic interest in the work, local knowledge, and seamanship is due much of the success of the venture. The party sailed from the Bluff on January 11, but was weatherbound for some days at Stewart Island. Preservation Inlet was entered on January 20, and the party returned to the Bluff four weeks later. During that interval about a hundred miles of coastline were studied, but time did not permit the investigation of the thickly forested region away from the coast, of which McKay's account with slight emendation is herein accepted. The authorship of the statement of the results has been shared. This introduction and the general account of the geology and tectonics has been written by Benson on behalf of all members and with their criticism. Part II, dealing with the geomorphology, is the joint work of Benson, Bartrum, and King; Part III (petrology) that of Benson and Bartrum; and Part IV (detailed Ordovician stratigraphy and description of the graptolites) that of Benson and Keble. Except as regards the descriptive palaeontology, the manuscripts have been prepared by Benson, and after mutual discussion edited by Bartrum. The scenic plates are from Bartrum's photographs, the illustrations of the graptolites were prepared by Keble, and the remainder of the drawings and maps by Benson.
Grateful acknowledgment must here be made of the help given by Dr. Marshall, and Professors Park and Speight in lending for comparative study microscope-slides of rocks from Preservation Inlet, the Green Islets, and Dusky Sound. Dr. F. J. Turner also lent the whole of the material studied by him in connection with his petrological investigations in the Haast and Cascade Valleys, and helpfully discussed various points that arose. Through the courtesy of the Surveyor-General permission was granted for the use of Mr. T. W. Preston's recently completed but unpublished map of Dusky Sound.
The region investigated comprises three topographic elements (see Plate 41). There is a much-dissected highland rising to accordant summit levels, which decline from 4300 feet in the north-eastern corner to 3300 feet a few miles from the coast. Hereinafter the highland surface, of which the peaks represent the last remnants, will be termed the maturely dissected Fiordland Peneplain. Near
the sea the land drops rather rapidly to 1500 feet, whence there extends a youthfully dissected coastal plateau sloping often convexly towards the coast-line five or ten miles distant, where it ends in a sea-cliff 100 feet to 400 feet high. Crossing the coastal plateau are two major inlets, Chalky and Preservation Inlets, representing the third topographic element, each partly closed by a large island, Chalky and Coal Islands respectively, covered wholly or in large part by thick Tertiary sediments. The surface of both of these islands is a continuation of that of the coastal plateau, though smaller islands which do not rise to the height of that surface lie further within each inlet. Dividing the two inlets one from the other is Gulches Head, a tied island, almost severed from the mainland by the embayment of Southport. From either inlet a long, deep, and narrow fiord with characteristic threshold extends into the region of the Fiordland Peneplain, broadly rectilinear in both cases, and, in the case of Chalky Inlet, dividing into two branches, Edwardson and Cunaris Sounds respectively.
Apart from a partial cover of glacial and other post-Tertiary débris, the region studied is composed essentially of a very thick series of fine-grained, closely-folded Lower Ordovician sediments, invaded medially by great batholiths of granitic rocks elongated in a direction approximately N.W.-S.E., and injected with the accompaniment of thrust from the west, with resulting regional and contact-metamorphism of the sediments which became folded in the same orogeny. Above them, on their south-west side, there is a relatively narrow N.W.-S.E. coastal belt of Tertiary sediments, which locally also cover protruding granite. Just north-east of the line of trend of the inner margin of this belt, Lower Ordovician graphitic slates contain a fine sequence of graptolite faunules, which disappear north-eastwards with the increase of metamorphism on closer approach to the batholithic granite.
In the north-east corner of the region, at the head of Long Sound, there is a series of calc-silicate and other metamorphic rocks in which calcareous layers have been prominent in the original sediments, and which display intensely complex small-scale folds. The age of this Long Sound Series is indefinite, but evidence will later be presented in favour of its being Upper Ordovician and metamorphosed prior to the date of the batholithic injection. As a late effect of this injection, various quartz veins were formed by escaping solutions, and were involved in a general westerly-directed movement of thrust of a date subsequent to the earlier eastward thrust.
As will be shown in the appended summary of the stratigraphic and tectonic characters of the various formations, Tertiary sedimentation was preceded by a vast unrepresented interval, and has been followed by certain interesting tectonic movements.
Fossiliferous Ordovician Rocks.
The Ordovician rocks occur in their least altered form near Cape Providence, in the northern part of Gulches Peninsula, and about Preservation Inlet. They may be traced thence passing with increasing metamorphism northward along the shores of Chalky Inlet and Edwardson Sound, and thence eastwards by way of Cunaris Sound to the middle portion of Long Sound, where they are highly metamorphosed schists. They lie in simple, open folds on the western shores of Cape Providence (see Plate 42A), but in more tightly compressed folds about Preservation Inlet, and still more so in Chalky Inlet and its branches and in Long Sound. These folds, though not overturned, are often asymmetrical with their axial planes dipping steeply towards the west. The stratigraphical succession has been determined palaeontologically by the discovery of over thirty fossiliferous localities, sixteen on Cape Providence, thirteen on the southern shores of Preservation Inlet, two on the north-western shores of this inlet, and one on the northern part of Gulches Peninsula. From these, over eighty species of graptolites were obtained, most of which are identical with Victorian forms, though sixteen are new. Their relative position in the sequence is in general clear on stratigraphic grounds, and the successive faunal assemblages agree with those of Victoria. There are also several sponges provisionally referred to Protospongia and Stephanella (?), undetermined phyllo-carids, and an obscure obolid (?) brachiopod. In a previous paper (Keble and Benson, 1928) the Lower Ordovician rocks of New Zealand were grouped tentatively into two major series, which we shall now term “Divisions.” Of these, the lower was left unnamed, and comprised the “Preservation Zone,” now recognised as the equivalent of the Lancefieldian Series of Victoria, and also the then undiscovered equivalent of the Bendigonian Series of Victoria. The higher or Aorere Division contained the Golden Ridge and Douglas Series, the equivalents respectively of the Castlemanian and Darriwillian Series of Victoria. As a result of the present investigations, the equivalent of the Bendigonian Series has been found, and the name Fiordland Division is suggested for the lower major Division, thus containing the New Zealand representatives of the Lancefleldian and Bendigonian Series. Moreover, it is now possible to recognise two zones in the Lancefieldian and three, or perhaps four, in the Bendigonian. Two zones may be distinguished in the Castlemainian beds, and the presence of a third is indicated by material obtained from pebbles. In order to avoid unnecessary duplication of stratigraphical names, the Victorian series-names will be employed to denote their precise equivalents in New Zealand.
The Lower Ordovician sediments comprise quartzite, greywacke, and grey or black carbonaceous graptolitic argillite. Even the least altered rocks show the first traces of metamorphism by the development of spots in the responsive pelitic layers. Occasionally a little calcite or siderite occurs in the argillite.
Intrusive Plutonic Rocks.
The Ordovician rocks described above have been invaded by a series of batholiths, about which is both regional and contact meta-morphism. The batholiths lie for the most part in the outer portions of the region showing contact-metamorphism, so that their contact along their south-western borders is with slightly altered sediments, while that on their north-eastern margins is with strongly schistose metamorphosed sedimentary rocks. From the petrological viewpoint, the former constitute the upper and the latter the lower metamorphic zone, a contrast which, it will appear, has considerable tectonic significance. The batholiths consist chiefly of granodiorite and granite, but there is also a small sill-like mass of norite.
Metamorphism of the Lower Ordovician Rocks.
Metamorphic changes of regional character are displayed by the development of spotted phyllites, fine and more coarsely granular mica-schists, and porphyroblastic mica-schists and paragneisses. The more pelitic formations yielded readily to lateral compression, and highly schistose rocks resulted, whilst the greywackes tended rather to recrystallize statically with preservation of their original sedimentary structures, including lamination and current bedding, but with entire change of their original microscopic features. These changes are traceable with increasing intensity northwards and eastwards to the heads of Edwardson and Cunaris Sounds and into the middle part of Long Sound. Here, interbedded with schists and paragneisses, are relatively thin bands of calc-silicate hornfels-schists. Here, too, are the lower contact-metamorphosed schists.
Long Sound Series (? Upper Ordovician) and its Tectonics.
The north-east extremity of Long Sound shows sediments, apparently of a different type from elsewhere, in intensely crumpled beds, which appear to be overthrust to the north-east and enter into lit-par-lit contact with invading granodiorite. Petrologically they are feldspathic quartzites, calc-silicate hornfels-schists, and rarely mica-schists which were originally greywacke, marl, and mudstone, and there are unmistakable points of analogy with the rocks at Last Cove, further west in the same sound. For reasons to be advanced, these rocks are provisionally held to be Upper Ordovician sediments crumpled and overthrust before batholithic granitic intrusions that came up from the south-west during a phase of easterly-directed thrust, invading the almost meridionally folded sediments. The last expression of this compressional movement after the consolidation of the batholiths was overthrust faulting in the same direction represented by the Last Cove Fault.
Tectonic movements subsequent to the above suggest the action of the reverse member of the thrusting couple, namely, an over-thrusting westward among the formations in the higher metamorphic zones, with the production of low-angle thrust-planes, as well as several series of nearly vertical fracture or shatter lines, along which differential movements took place, which caused movement relatively to the east on the north side of each fracture.
Quartz Veins, Minor Basic Intrusions.
The development of more or less mineralised quartz veins occurred just before and during the last movements. Apart from the apophyses obviously related to the batholithic intrusions, and the norite, the age and affinities of which are as yet indeterminate, there have been observed a sill of dolerite and a dyke of lamprophyre.
Tertiary Sediments and Their Structure:
After a prolonged unrecorded interval came the deposition of Tertiary sediments, beginning with arkosic basal conglomerates, sands, and mudstones accumulated in confluent fans and deltas, and incorporating swamp deposits containing small coal seams. These were covered by more sands and mudstones, followed, as the submergence became deeper, by thick marly sediments containing fora-minifera.
Warping followed along N.W.-S.E. axes crossed by that along N.E.-S.W. axes. This was succeeded by the complicated sequences of geographic changes, culminating in the Pleistocene glaciation, that have determined the modern topography. These are discussed in detail in Part II.
Preliminary Account of the Lower Ordovician Stratigraphy and Faunal Succession.
Detailed account of the stratigraphy of the Lower Ordovician rocks must await the final results of the examination (now almost completed) of the large collections of fossils obtained from these beds. Provisional study of these, however, has yielded results so consistent, both with the apparent stratigraphical succession in this region and with the known faunal succession in Victoria (Harris and Keble, 1931), that a preliminary statement of them is authorised by Mr. Keble, who has the palaeontological investigations in hand, and has prepared the following explanatory paragraph.
“It is proposed to form two divisions in the Lower Ordovician rocks of New Zealand. The older, the unnamed ‘series’ in an earlier paper (Keble and Benson, 1929), will be termed the Fiord-land Division, the younger or Aorere ‘series’ will become the Aorere Division.* The Fiordland Division presents that phase of graptolite development in which dichotomy is the dominant character and thecal specialisation is less evident, while of the Aorere Division the reverse is true. The Fiordland Division has been subdivided into
[Footnote] * In the paper of 1929 the Preservation and Lancefield beds were referred to “zones,” but Harris and Keble (1931) have reverted to Hall's use of the term “series” for the latter, and a consequent change has here been made in the naming of the New Zealand beds. It appears desirable to postpone the systematic application of the ordinal terms “series,” “stage,” and “zone” to various portions of the Ordovician system in New Zealand until more detailed palaeontological data are available. Meanwhile the terms “series” and “zone” are used herein in the same sense as they are now applied to the Victorian beds (Harris and Keble, 1931), in which no divisions corresponding in ordinal rank to the Fiordland and Aorere Divisions have yet been instituted.
two series, equivalent respectively to the Lancefieldian and Bendi-gonian Series of Victoria, for which, if New Zealand names are required, the terms Preservation and Dark Cloud Series† might be suggested. The Lancefieldian (or Preservation) Series is the lower, and common to it are forms in which dichotomy occurs at irregular intervals; in Bryograptus, Clonograptus, and even in some forms of Tetragraptus the dichotomising character is often recessive, stolonal thecae only appearing at intervals during which one or more brachial, thecae are developed. Under such conditions the resulting polypary is unsymmetrical. On the other hand, in the Bendigonian (or Dark Cloud) Series, dichotomy is consecutive, and the branches, arising from the stolonal thecae, usually grouped nearest to the sicula, form a polypary both symmetrical and balanced; characteristic of this series are Tetragraptus (sensu stricto), Dichograptus, Goniograptus, etc. The lower, Castlemainian (or Golden Ridge) Series of the Aorere Division is marked by the development of Didymograptus caduceus in its multiplicity of mutations resulting from thecal specialisation and phylogenetic development, and towards its close by the appearance of such biserial forms as Diplograptus, Trigonograptus, etc. In the upper Dariwillian (or Douglas) Series of the Aorere Division the biserial forms are doubtless much more evident, and herald the approach of that character as the dominant feature of the Upper Ordovician rocks, the Mt. Arthur Division.”‡
The type section of the region is that running along the coast north-west of Cape Providence. It is confirmed and supplemented in some respects by the more strongly folded beds traced along the southern shore of Preservation Inlet from Kisbee Beach to Coal Island. The lowest beds are exposed a mile and a-half north-west of Cape Providence, where they are but gently flexed (see Plate III, Fig. A), perhaps also on the northern end of Gulches Peninsula, and again between Kisbee and Te Oneroa Beaches, at the north-east corner of Coal Island, and in Te Whara, in Preservation Inlet. In all but the first locality the beds dip steeply. These beds belong to the Lancefieldian Series, of which a thickness of nearly 3000 feet is exposed above concealed underlying formations. The lower portion may be correlated with the L3 zone of the Victorian Lower Ordovician beds. It is characterised by the presence of Tetragraptus decipiens T. S. Hall, with a very subordinate development of Dictyonema macgillivrayi T. S. Hall, Clonograptus cf. magnificus Pritchard, Bryograptus clarkei T. S. Hall, Bryograptus victoriae T. S. Hall, and seven other forms. The higher portion, best displayed between Kisbee and Powell's Beaches, is characterised by the association of T. decipiens T. S. Hall, with an abundance of Bryograptus pauxillus sp. nov. and Clonograptus kingi sp. nov., and sixteen other forms.
[Footnote] † Commemorating Captain Cook's alternative name for Chalky Inlet.
[Footnote] ‡ This remains true, though recent Victorian investigations indicate that it is desirable to transfer to the base of the Upper Ordovician the richly fossiliferous Cobb beds of the Mt. Arthur region, which were formerly considered the highest member of the Darriwillian (Douglas) Series. See Thomas and Keble, 1933, pp. 42 and 54.
This portion of the succession seems comparable with the L2 zone in Victoria. No faunal assemblage such as that in the L1 zone of Victoria has yet been found in New Zealand.
Two hundred feet above the highest fossiliferous horizon in the series last described, there occurs a bed containing Tetragraptus fruticosus (J. Hall), the index species of the Bendigonian Series of Victoria. It here displays the early four branched form, and is accompanied by Tetragraptus approximatus Nich., and Tetragraptus acclinans Keble, the association characteristic of the lowest or B5 zone of the Bendigonian Series, together with eighteen other species. This assemblage is partially displayed a mile north of Cape Providence, and more fully between Kisbee and Powell's Beaches in the south-eastern corner of Preservation Inlet.
The equivalent of the B4 zone on the Victorian sequence has not been seen in situ, but a boulder obtained nearly a mile north-west of Cape Providence showed the four-branched form of T. fruticosus (J. Hall) unaccompanied by T. acclinans Keble, T. approximatus Nich., or T. decipiens T. S. Hall, but with Goniograptus macer T. S. Hall, an association which would characterise the B4 zone in Victoria. This zone must, however, be very thin here, for three hundred feet above the B5 fauna there is a bed containing the three-branched form of T. fruticosus (J. Hall), a great abundance of Phyllograptus typus J. Hall, and thirteen other species, forming an assemblage which would be found in the B2 zone in Victoria.
One to two hundred feet higher still the three-branched form of T. fruticosus (J. Hall) is associated with Didymograptus bifidus (sensu lato), together with twenty-six other species, constituting an assemblage which is characteristic of the B1 or highest zone of the Bendigonian Series of Victoria. Thus the presence of four out of the five zones in the Bendigonian Series hitherto unknown in New Zealand would seem to have been demonstrated. It is to be noted that they are comprised within a thickness of 600 feet of strata, while in Victoria the equivalent strata are generally more than 2000 feet thick. The Bendigonian beds on Cape Providence consist of argillites and greywackes, and are bent into a broad synclinal fold, the characteristic B2 fauna appearing on either side of the axis, while the central portion of the syncline is occupied by Castlemainian beds.
The equivalents of the Castlemainian Series of Victoria have long been known in New Zealand, and from their presence in the northern portion in the South Island they were termed the Golden Ridge Series. They were first found in the south-west of the island, at Cape Providence, by Professor Park (1922). His collection, according to verbal accounts kindly given to the writer, was obtained from a spot about half a mile north-west of the cape. Nineteen species were recognised therein by Keble (1927), who referred the collection to the C4 zone of the Castlemainian Series as then understood. Additional material has now been obtained. In the axial portion of the abovementioned syncline, about one hundred feet above the highest bed yielding Bendigonian fossils and a thousand yards north-west of the cape, there are beds which are free from T. fruticosus
(J. Hall), but contain an abundance of D. bifidus (sensu lato) associated with a small form of Isograptus caduceus (Salter) = I. gibberulus (Nich.), Dichograptus octobrachiatus (J. Hall), Tetra-graptus serra (Brongn.), T. similis (J. Hall), and sixteen other species, an assemblage which would characterise the basal Castle-mainian zone C5, to the upper portion of which Professor Park's collection should now be referred. A similar association of fifteen species occurs in a richly fossiliferous bed on the northern shore of Coal Island, lying in regular sequence above fossiliferous Bendigonian and Lancefieldian beds.
The central portion of the syncline on the western side of Cape Providence is occupied by sparsely fossiliferous beds in which the dominant form is Isograptus caduceus (Salter), mostly small, but tending to become larger. “D. bifidus” no longer occurs, but D. dependulus H. and K. is present together with Tetragraptus woodi Rued, and a Diplograptid, an association of forms which may be correlated with that in the C4 zone in Victoria, as now defined by Harris and Keble (1931).
Among the pebbles gathered from the Cape Providence beach are graptolites from almost all of the above zones, but the presence of Loganograptus logani (J. Hall) in one pebble and of a large form of Isograptus caduceus (Salter) in others, both obtained from the eastern or Landing Bay side of the point, indicate that Upper Castlemainian beds belonging to the C2 or C1 zones must occur in the vicinity.
The total thickness of proved Castlemainian beds is about two hundred feet, but the presence of the two species last mentioned indicates that the actual thickness in this region may be considerably greater. There is no sign of the presence of any Darriwillian forms, or other forms derived from any higher series.
It thus appears that collections obtained from both sides of the syncline on Cape Providence, and in regular stratigraphic sequence along the southern shores of Preservation Inlet, have been shown to contain the same faunal zones as have been determined in Australian rocks, the very clearly displayed structural relationships of the several beds affording a most satisfactory check on the correctness of the faunal succession.
Unfossiliferous and Metamorphic Ordovician Rocks.
Leaving for fuller description in Part IV the typical sections of fossiliferous Ordovician strata, attention may be turned to the unfossiliferous and metamorphic formations associated with them. The petrographical nature of their rocks is discussed in Part III, but their field occurrence will be noted here. The four principal types of sediment are quartzite, greywacke, grey argillite, and carbonaceous black argillite. Commencing in the least altered regions, Crayfish Island exhibits these four types of rock, the greywackes on its west coast displaying both current-bedding and ripple-marking. The strike is generally N.N.W. with a steep westerly dip, but at the northern end of the island …“the rocks have been greatly disturbed, and are seen striking directly across the general trend of the
(Ordovician) belt of country” (McKay, 1896), whilst shatter zones running slightly north of due east traverse them. In Long Island jointed quartzites and greywackes alternate with graphitic slates showing strain-slip cleavage. Round Island consists of shattered quartz-veined siliceous greywackes, and the Cording Islets of quartzites, grey and spotted argillites. The last show considerable disturbance of the line of strike, and are broken across by several sets of shatter-zones. North of Kisbee Bay a sequence of contact-meta-morphosed rocks was obtained by Keble, including quartzose biotite hornfelses derived from greywackes, and cordierite hornfelses derived from argillite. The latter, when in the immediate vicinity of the intrusive granite, show extremely well-developed and abundant cordierite, and similar rocks were collected by Marshall in 1930 from glacial erratics at Te Oneroa Beach. On the eastern side of the entrance to Isthmus Sound, Hutton (1875, p. 40) observed masses of slate included in the granite with slight alteration at the immediate contact. The line of contact passes through the north-easternmost part of the Cording Islets on the western side of the entrance, and appears to be displaced laterally by a fault. In Brokenshore Bay greywackes are in contact with a coarse granite, rich in pink orthoclase, along a very sharply defined and irregular boundary. On the northern shore of the bay the greywacke becomes lighter in colour adjacent to the granite and more coarsely crystallized, and near the junction is almost indistinguishable from granodiorite, which, in fact, intervenes in small amount between the granite and the greywacke, making an undetected contact with the latter. Traced westward, the metamorphism rapidly diminishes, but the more responsive argillites are here scantily developed. At Rounding Head, between Brokenshore Bay and Cuttle Cove, a band of argillite appears to have been changed with the development of cordierite, now entirely replaced by quartz. Nearer the cove a narrow diorite dyke is fringed with a well-crystallized biotite hornfels. The rarity of argillite bands and of preservation of bedding planes renders impossible a detailed study of the folding suffered by the beds here, but a sharp anticline is exposed south-west of Cuttle Cove, where spotted argillites occur. At Cavern Head the massive quartzites are broken by a series of quartz-filled tear-veins running in a east-north-east direction, and adjacent thereto there is local deflection of the general meridional strike into a north-east direction, probably as a result of drag along this line of tearing. The rocks showing this disturbed strike are intermediate in character between argillites and quartzites, and nearby is a zone of graphitic micaceous argillite containing a formerly exploited quartz reef. Near the beach north-west of Cavern Head, Hector (1863) noted a dyke of porphyritic granite invading the argillite. A series of finely-bedded, locally puckered argillite or fissile shale, shattered greywacke, and quartzite extends between Cuttle Cove and Seek Cove, and forms also the Spit Islands, Te Whara, near which graptolites of the Lance-field series occur. These rocks are thrown into sharp folds and broken by shatter or shear-zones parallel or oblique to the strike, whilst the increasing development of sericite gives a phyllitic appearance to the argillite. The change is more marked at the eastern side of the entrance to Southport, where the rocks are clearly subschistose and
contain spotted bands. This schistosity results from the development of sericite with flakes of biotite more or less changed into chlorite, and is particularly well displayed in Garden Island and the eastern portion of the islets to the north of it, where the rock is a pale greenish or brownish, silky sericite-schist, slightly sheared or puckered, and resembles the schist of Central Otago more nearly than any other formation in the Preservation Inlet district. On the eastern half of the northern islet it is interstratified with a thin layer of amphibolite, and dips westward at at angle of about 35°, but the western half of the islet consists of a mass of intensely sheared or mylonitised schist dipping steeply westward at 62° and containing abundant long slickensided lenticles of quartz. This mass strikes in a meridional direction, and marks an important fault-zone with down-throw to the west, which is here called the Southport Fault, and extends through the strait west of Garden Island, and probably along the eastern shore of Gulches Peninsula. The northern portion of this peninsula, meanwhile, consists of perfectly normal quartzite, greywacke, and argillite containing obscure graptolites, sponges, and phyllocarids. Its horizon is uncertain.
Continuing northwards along the coast of Chalky Inlet, the schistose character of the argillite and the spotting become more evident, though the associated greywacke shows clearly current-bedding and ripple-marking, and at a point near Surf Head irregular crumpling of lamination resulting from slumping of the sediments during their accumulation is clearly displayed. Hector (1863) very appropriately described these rocks as “… an interesting group of siliceous felstones, greenstones, glossy claystones, and mica-schists.” The structural features observed during this northward traverse are a swinging of the regional strike from a meridional into a north-east direction, the presence of a syncline and the occurrence of several vertical, approximately east-west shatter zones.
New features appear at the entrance to Cunaris Sound. Crystals of biotite about half a millimetre in diameter have developed in the recrystallisation of the finer greywackes, while the base has become either granulitic or schistose and sericitic, and, traced northwards into Edwardson Sound or eastward along Cunaris Sound, these petro-logical features become so strongly evident that the rocks appear like fine-grained gneisses, and were so termed by Hector, though mistaken for granite by Linck. They may be termed porphyroblastic paragneisses. Their metamorphism has been very largely the result of recrystallization under static conditions, for on some weathered surfaces they still display original current-bedding, unobliterated by development of schistosity, just as clearly as do the unaltered rocks on Cape Providence, with which they seem to have been identical. In other cases it is evident that the rocks had been shattered and sheared before subsequent recrystallization completely changed their microscopical structure, for thin sections and recently fractured
surfaces give no hint of such major structures, though they are often clearly etched out by weathering. Interstratified with these rocks are typical biotite-sericite-schists, with well-developed schistosity usually parallel to the bedding plane. The spotted structures have considerable persistence, but become gradually obliterated in the formation of biotite-schist and paragneiss. Though there is an average increase in grain-size towards the east and north, there is great variation in this respect, and more or less finely laminar and fine and coarsely granular paragneisses are interbedded. In addition there are included quartzites, which are greenish, and tend to become vitreous by recrystallization. A peculiar layer consisting of sericitic quartz-amphibolite, probably derived from a band of dolomitic marl a few feet thick, has been noted at the head of Edwardson Sound and near the entrance of Cunaris Sound, and again near its head. At two or three points dykes of diorite or aplite radiating from the Treble Mountain massif reach the southern shore of Cunaris Sound, while the margin of the massif itself touches the shore of Islet Cove. Structurally it is to be noted that the strike of the sediments has returned to the meridional trend, and that a series of anticlinal and synclinal axes cross Cunaris Sound perpendicularly, whilst fault planes dipping east at low angles and overthrust to the west are visible at a number of places.
No geologist has traversed the valley of the Carrick River entering Cunaris Sound, but as Linck (1896) noted that the pebbles in its delta consist “…mainly of mica-schist, quartzose schists, and quartzites, with only a small percentage of granite,” it appears probable that there is little plutonic rock in its watershed, and the Long Sound Series is well represented.
Save for the absence of plutonic apophyses, the rocks of the northern shore of Cunaris Sound are precisely the same as those on the south, though no correlation of individual bands has yet been possible. The same types of rock continue up the eastern shore of Edwardson Sound, where they show an alternation of rather glassy quartzites with a predominance of medium or fine-grained biotite-sericite-quartz-schists, and of porphyroblastic biotite-paragneisses of varying grain-size and degree of schistosity. Some bands are almost massive. In one instance it appeared possible that the schistosity was not parallel to the bedding planes of the original sediments. According to Linck, schistose rocks form the mountains on either side of Lake Cadman, an inference supported by their topography, whilst similar rocks also surround the head of Edwardson Sound. The strike of these schists swings almost into parallelism with Edwardson Sound, near Divide Head, but bends to the north and north-north-west nearer to the head of the sound.
The western coast of Edwardson Sound is almost rectilinear, and runs approximately parallel to the margin of the plutonic rocks of the adjacent batholith, whilst evidences of shearing can be noted both in the field and under the microscope in the rocks along this boundary. The most massive block of schist marginal to the granite is a narrow coastal strip, about a mile in length, situated about three miles south-west from the head of the sound. Its rocks are schists of medium to coarse grain-size associated with the usual paragneisses, but the appearance in them of large flakes of white mica is, however, a new feature resulting from contact-action. This latter is very marked along the shore further south-west, where, for two miles from the southern end of the main strip of schists, the contact between the igneous and metamorphic rocks is beautifully displayed on the glaciated surfaces of the low promontories as a zone of brecciation and interpenetration of schist by granite and ramifying veins of quartzose pegmatite, along which large fragments and strips of schist appear included in the granite. This has led to the development of very coarsely crystalline almost gneissic schists with large flakes of white mica as well as of biotite, whilst in certain layers at the contact there are grains of a bright yellow epidote (or clinozoisite), and locally some felspathisation has taken place. The rarity or indeed absence of garnetiferous schists is noteworthy. This mass of rocks will be referred to in Part III as the Edwardson intrusion complex.
Similar contact-schists occur on the southern portion of Little Island and the north-eastern part of Great Island, but it is uncertain whether or not they occur in the south-eastern part of Passage Island. Masses of schist also form large inclusions ramified by veins of diorite, granite, aplite, or pegmatite in the vicinity of Northport. They have been found in the valley of the stream draining Lake Cæsar, at the head of the cove by Mosquito Point, and in the promontory south of the western entrance to Northport (Blind Entrance). As frequent reference must be made to this locality, it will hereafter be termed Blind Point. At this locality the complex of schists and invading aplite and pegmatite is very involved. The strike of the schists has been deflected to the north-east, and their facies include felspathic quartz-chlorite schists and sillimanite-biotite schist, the latter with coarse epidote (or clinozoisite). Biotite schists also occur in large included masses at Lake Cæsar Creek, and are probably fragments of a large roof pendant or an infaulted strip of schist along the line of Northport fracture. They do not extend any distance to the north of this line, as the pebbles in Shallow River are all igneous. On the authority of two miners, Linck (1896) doubtfully indicated the presence of slate between Breaker Point and Landing Bay, but observations made during two traverses overland and from the sea make it probable that this area consists of granitic rocks.
The series of schists occurring in Cunaris Sound extends across the narrow isthmus into Last Cove in Long Sound, and continues eastward with increasing grain-size and schistosity. The most coarsely crystalline of the moderately and markedly poikiloblastic paragneisses, of the quartz schists, and of the mica schists occur along the north coast of the sound, extending three miles east of Last Cove. Here, as elsewhere, there is a close association of fine and coarsely granular schists, and the occasional retention of the original bedding planes made evident on the weathered surfaces of massive rocks. Schists may contain lenticular segregations or irregular bunches of quartz or thin laminae developed in the planes of schistosity, but the quartzites are either hard grey-blue almost glassy rocks, or micaceous and almost saccharoidal, both types being fractured and seamed by quartz-veins. Similar rocks form the promontory immediately south of Last Cove, but are interlaminated with calc-silicate hornfels-schist, which on weathered surface has a very characteristic fluted appearance. It forms here a narrow band in the normal biotite-schists, and the same is true of a layer occurring a mile east of Last Cove and of another five miles to the east-north-east on the islet between Only Island and the southern shore. These rocks must have been derived from layers of dolomitic marl within original sediments composed of laminae of varying composition. Their present nature is clearly the result of heating by adjacent intrusive masses, as well as of regional compression. A band of coarsely flaky biotite-sillimanite-schist with small “augen” of orthoclase, occurring adjacent to a slabby, finely granular mica schist a mile east of Last Cove, is also a product of deep-seated contact-metamorphism, as are also the coarse quartzose mica-schist, the knotted andalusite schsts, and pinite (?) schists on the southern shore of the sound adjacent to the granodiorites.
Injection-schists showing a very high degree of intensity of metamorphism occur about half a mile south of Only Island, in the headward portion of Long Sound, whilst the whole development of schists in the middle portion of this sound lies within the influence of plutonic intrusions, which occur in force on the southern shores, but are represented for about three miles of the northern shore only by an occasional dyke of aplite, granodiorite, or norite. Larger masses occur on either side of this length of shore and enter into lit-par-lit injection into the schists immediately west of Last Cove.
Structurally, all these schists dip very steeply either east or west of a strike line trending a little west of true north. They are cut off to the west by the Last Cove fault, which dips to the south-west at 50°, and by which the Treble Mountain granite massif has been thrust to the east. The clearly displayed passage of Ordovician sediments comprising fossiliferous beds into thermally and dynamically metamorphosed rocks finds close analogies among the formations of south-eastern New South Wales (Browne, 1914) and north-eastern Victoria (Tattam, 1929).
The Long Sound Series.
The rocks classed in this group extend for nearly two miles southward from the head of Long Sound, and have been examined most closely along the northern shore. They are probably a portion of the schists grouped by Hector as “mica-schists, feldspathic gneiss, and quartzites.” In general of fine to medium grain-size, they are well laminated, alternate layers being largely quartzite, with scattered mica and thin streaks of felspars and calc-silicates, or grey speckled calc-silicate laminae consisting largely of minerals such as quartz, bytownite, diopside, ilmenite, and calcite, or grey-brown with abundant biotite. They weather into an ochreous or rusty mass. Their peculiar composition indicates their derivation from a series of sediments composed of alternating layers of feldspathic sandstone, dolomitic marls, and claystone. They now occur in close-packed folds broken by small faults and thrusts as illustrated in Plate 43B, a photograph taken a mile from the head of the sound. The folds are often overturned and almost recumbent, so that a cliff face about 1200 yards from the head of the sound exposing a number of such folds superposed one on another resembles a pile of folded blankets, each fold being from three to ten feet thick. On the east side of the head of the sound the cliff face of Houseroof Hill reveals on a larger scale the same intricate folding. Though it is unsafe to generalise from a small number of observations of dip in so highly disturbed a formation, the strike appears to be nearly meridional or to the east of north, the dip generally to the west at low angles, and the folds almost invariably overturned to the east. Striations on the exposed surface of the folds indicate some slipping in the direction of dip, whilst an appearance of striation perpendicular thereto arises from minor strain-slip movements parallel to the strike.
On their western limits the rocks of the Long Sound Series are cut off by granodiorite, which invades them in characteristic lit-par-lit injections, particularly well displayed in an isolated mass of these rocks in the cove immediately north of Only Island (see Text Fig. 1). Nowhere along the northern shore of Long Sound do these rocks come in contact with those described in the last section (p. 409). On its southern shore the evidence is even less clear. The crumpled schists of the Long Sound Series have been traced south along this shore to a promontory nearly two miles south of the head of the sound, and are then replaced for about a mile by plutonic rocks; these are followed in turn by a further mile of schists which continue to Only Island, where they show lit-par-lit invasion by granodiorite. The schists of this last portion of the coast showed no obvious litho-logical or structural difference from those further west, but adverse weather conditions did not permit of as close an examination of them as desirable, so that possibly here the relation between the Lower Ordovician sediments described in the last section and certain interesting calc-silicate rocks at Last Cove may be ascertained in the future.
Text Fig. 1.—Lit-par-lit injection of granodiorite into the calc-silicate schists of the Long Sound Series. Observed on the north shore of Long Sound, opposite Only Island. Direction, left to right, is S.W. to N.E.
There is, however, sufficient petrological evidence to suggest very strongly what that relation may be. As will be shown in Part III, the remarkable mineral composition of the siliceous Long Sound rocks, with their quartz, microcline, and diopside, is repeated by one of the bands of the calc-silicate hornfels-schist at Last Cove. The composition of the finely granulitic grey layers in the Long Sound rocks, with its quartz, basic plagioclase, diopside, ilmenite, and red-brown sphene, is repeated by a thin layer in the islet adjacent to Only Island, which has further petrological links with the Last Cove rocks. The micaceous layers among the Long Sound rocks and the quartzitic layers in the mass north of Only Island have also analogies among the schists near Last Cove. Obviously it is out of the question to correlate thin layers of calc-silicate rocks with the great thickness (a thousand feet or more) of the Long Sound Series. What is suggested, however, is that the calc-silicate rocks in the Ordovician schists of the middle part of Long Sound indicate the entry into the Ordovician sedimentation of a marly or calcareous phase that found fuller expression in marly quartzites, marls, and mudstones, which now have been converted into rocks of the Long Sound Series. In this connection reference may be made to Park's (1888) account of Cooper Island and the parts of Dusky Sound fifteen miles north, or along the line of strike from the head of Long Sound. The rocks are described as “granite gneiss which passes into felsitic schists, and contains beds of mica schist and crystalline limestone,” or again as “coarse arenaceous mica schist passing into felsitic schist, which forms frequent transitions into or alternates with mica schist, quartzites, hornblende schists, chlorite schists, talc schists, and contains several bands of crystalline limestone.” A “gneissic schist with orthoclase,” recalling the augen schist of the area now described, is
also recorded, but the absence of any marked crumpling of the beds is noted. Their westerly dip is, however, at lower angles than that of the schist near the sea. As noted above, the watershed of Carrick River intervening between Dusky and Long Sounds appears to be occupied chiefly by schists, though their nature has not been ascertained, so that the continuity of the two more or less calcareous series of schists may be suggested. Moreover, occurrences of crystalline limestone are known in certain other of the northern sounds, viz., Doubtful, Thompson, Caswell, and Milford Sounds,* so that the former existence of an extensive calcareous formation among the schists of Fiordland is apparent. That it may continue further south is indicated by McKay's (1889) note of presence of marble in the north-western extremity of Stewart Island, and the occurrence of schistose calc-silicate hornfels forming a roof pendant in granite at the summit of Blaikie's Hill in southern Stewart Island. According to private communications from Dr. G. J. Williams, who discovered this hornfels, its strike is parallel to that of the adjacent mica schists which also forms large roof-pendant masses. Petrologically, the calc-silicate hornfels shows the closest similarity to rocks of the Long Sound Series, an important fact the citation of which is permitted here through the courtesy of Dr. G. J. Williams. A massive calcareous series also (the Mt. Arthur Series) has long been known in association with the Ordovician sediments and schists in the northern extremity of the South Island of New Zealand, and correlation there-with of the southern calcareous rocks may be a reasonable working hypothesis. The relation of the Mt. Arthur rocks to the Lower Ordovician graptolitic sediments has long been in dispute, but the most recent work of the Geological Survey leads to the conclusion that the Mt. Arthur beds belong to the Upper Ordovician, and follow conformably the Lower Ordovician formations.†
Provisionally, therefore, it would appear to be possible that the intensely folded rocks of the Long Sound Series may result from the local crumpling of a series of Upper Ordovician sediments which have been involved in the region of most intense metamorphism. If so, it may be that the rocks of the supposedly pre-Cambrian Dusky Sound Series of Park (1921), to which these would be assigned on the basis of degree of metamorphism, comprise formations actually younger than the far less altered rocks of his Lower Ordovician Preservation Series (the Lancefieldian, Bendigonian, and Castlemainian Series of the present paper), but it is by no means proved yet that this is the case. The cause of the very marked easterly-directed crumpling of the Long Sound Series is considered in a later section.
The Intrusive Rocks.
The major occurrences of plutonic rocks fall into two larger and two smaller masses. The two larger may be termed respectively the Bald Peaks-Treble Mountain massif, which is divided by Long
[Footnote] * See Morgan, P. G., 1927, p. 66, for references.
[Footnote] † See Keble and Benson, 1928, for statements based on Grange's field work.
Sound, and the Great Island-Kakapo Range massif, which is divided by Northport. So similar is the range of rocks in these two masses that they are probably united beneath Chalky Inlet. The granitic boss on Gulches Head is the third of these occurrences, and may be a cupola arising from the same great batholith as gave rise to the massifs mentioned above, the extension of which beneath the surface to the south and west is suggested by “spotting” and development of tourmaline in the Ordovician sediments there. The fourth mass, the Long Sound massif, crossing the middle portion of that sound, probably does not extend far to the north, as it is certainly not widespread in the watershed of Carrick River. On this view of the batholithic continuity of several of these plutonic masses, there are but two main intrusions—the huge, only partially deroofed Bald Peaks-Kakapo Range batholith and the far smaller Long Sound massif, which differs petrographically and structurally from the major one. The former lies in the main between the slightly altered and the strongly altered Ordovician sediments, and is elongated (as far as the area of the present map is concerned) in a north-west-south-east direction. The latter lies within the strongly altered rocks, and its orientation is unknown. The observations of the present expedition have been made only along the shore lines, and are, therefore, far from complete, but agree with the general features of differentiated batholiths, and are interpreted in accordance therewith.
Bald Peaks-Treble Mt. Massif.
The major portion of the Bald Peaks-Treble Mountain massif would appear to be a coarse-grained granite, with large pink ortho-clase crystals—a handsome rock, which, as Marshall (1929) indicates, would form an excellent building stone, and could be quarried near deep sheltered bays. It forms the majority of the plutonic erratics between Kisbee Bay and Puysegur Point, and occurs in situ along the shores of Revolver and Useless Bays, Narrow Bend, and the southern part of Long Sound and most of Isthmus Sound. In the last region there are occasional inclusions of slate and of granodiorite and quartz-diorite. These last less acid rocks occur along its margin in the areas examined, but need not completely encircle it; they are strongly invaded by the granite, which may locally break through them and come into direct contact with the sediments. At the entrance to Isthmus Sound the rock in contact with the slate is granodiorite, according to an old chemical analysis (Liversidge, 1877), and at Brokenshore Bay, a little to the north-west from there, a very narrow mantle of granodiorite, strongly invaded by the granite, intervenes between the latter and the greywackes. Beyond this to the west, north-west, and north-east apophyses are known, dykes of diorite at Cuttle Cove and near Cunaris Islands, and of aplite near the entrance to Cliff Cove at the head of Cunaris Sound. Here, also, a steep bluff of diorite with diorite-pegmatite rises from near the water's edge, and in Cliff Cove itself a few yards of quartz-diorite-selvedge are exposed on the shore, the boundary of the granite extending thence to Long Sound. It is exceedingly significant that this steeply plunging margin of the batholith is cut off by a fault, which dips
at 50° under the batholith, and that the movement of that fault, as shown by the drag of the schists on the footwall, should have been an easterly-directed overthrusting (Text Fig. 3).
The Gulches boss has been little studied, though a rather fine-grained quartz-diorite rich in chlorite was noted alongside the fault between the inner and outer headlands of Gulches Head, and probably represents a marginal facies. According to Hector (1863), Red Head consists of coarsely crystalline granite with large flesh-red crystals of orthoclase, which doubtless represents the central acidic facies.
Great Island-Kakapo Range Massif.
The Great Island-Kakapo Range massif is separated from the boss at Gulches Head by Chalky Inlet. The nature of the granite rocks in Passage Island and in most of Great Island has not yet been ascertained, though the south-western promontory of the latter consists of a rather gneissic, porphyritic granite, with large red orthoclase crystals, which is veined by syenite-aplite. Near the beach at Landing Bay a quartz-syenite with large crystals of orthoclase invades in lit-par-lit fashion gneissic quartz-diorites and diorites, and is itself invaded by coarse pegmatite and siliceous biotite granite with slabby, modified basic inclusions. A few hundred yards north of the shore of this bay the valley of Lake Thomas Creek is cut in gneissic orthoclase-bearing granite, with foliation very well developed near its margin and directed N.37° W.
Suggestion that a roof-pendant or down-faulted portion of the roof of the batholith extend through the Northport area is afforded by the marginal character of the rocks therein. Gneissic diorites occur in force along the northern shore west of Mosquito Point, and the normal sequence of invasion is well displayed. Strongly gneissic amphibolite and diorite are invaded by granodiorite or aplite; grano-diorite by granite, aplite, or pegmatite; granite by aplite and pegmatite. All these rocks have also been found invading schists. The pebbles in Shallow River, which are mostly of granite, show the same order of succession, and invasions of gneissic microdiorite by granodiorite and of both by aplite can be seen in a single pebble. The watershed of this stream appears to be wholly in igneous rocks, and two overland traverses between Lake Hector and Landing Bay showed only granite or granodiorite.
The eastern boundary of the Great Island-Kakapo Range massif is probably in part a fault, for north-east of Anchorage Cove gneissic granodiorite near the contact shows marked shearing. Elsewhere its border is a complex injection-breccia, wherein the marginal granite and granodiorite invade the schists irregularly or in lit-par-lit fashion, whilst masses of schist are included in the granite, the whole complex being seamed with ramifying veins of aplite and very quartzose pegmatite. The structure is well displayed on glaciated salients by the shore from one to two miles south of the small cove on the mid-western shore of Edwardson Sound, and attracted the attention of both Hector (1863) and Linck (1896). South of this, the massive cliffs facing the entrance to Cunaris Sound seem to consist of pink
granite, and the same rock probably also forms the bare pinnacles of the Kakapo Range. Thus in this massif also, granodiorite and more basic rock-types seem to be confined to a narrow, marginal zone about an essentially granitic batholith.
The tectonic structure of the intrusive mass is not yet known, and, in particular, the direction of schistosity of the rocks near Edwardson Sound was not recorded, though it probably was north-east-south-west. That of the rocks near Northport was more nearly parallel to the length of that channel. If, then, the massif had in the main rectilinear boundaries along north-west-south-east and north-east-south-west directions, it would seem that, at the time of its intrusion, the folded Ordovician rocks had already been subdivided into blocks by two of the major fracture systems that are known throughout the region, trending diagonally to the general strike. Movements along these may have occurred at later periods and be illustrated possibly by trough-faulting along Chalky-Edwardson Sound itself.
Long Sound Massif.
The Long Sound massif is not well known, and its structure is possibly complex, though the total mass of plutonic rocks exposed may not be great. The section shown below the map (Plate 43) and Text Fig. 1 illustrate the conception formed of the occurrence, namely, that it is a small, broken, and irregular intrusion extending in a series of apophyses and lit-par-lit injections, which have been thrust mainly eastwards into the schists. Its western limit on the north shore of Long Sound appears to be along a fault about three miles east of Last Cove, though veins of granite and of aplite occur west of this fault. Lit-par-lit injections, both into the Lower Ordovician schists and into the rocks of the Long Sound Series, are well displayed on both sides of the sound near Only Island, whilst the igneous rock in turn contains many large inclusions of coarsely granular quartzose schist. The rocks of the massif are granodiorite or quartz-mica diorite, and rarely diorite, the invasion of the less siliceous by the more siliceous types being apparent in a number of cases. A dyke of coarse diorite-pegmatite invades the hornfelsic schists along the shore about a mile to the north-east of Only Island; gneissic structure is developed in it to some extent, but information as to its strike is very incomplete. In the lit-par-lit apophyses south of Only Island, however, the foliation dips at 80° E., with a strike N.33° E.
The Norite of Long Sound and Other Basic Intrusions.
The field-occurrence of the hornblende-norite early mentioned as outcropping in Long Sound is little known, as its plutonic nature was not recognised when the specimens were collected. It forms a small promontory by a waterfall on the north shore between two and a-half and three miles east of Last Cove, and thus midway between the latter and Only Island. As no indication of its making transgressive contacts was seen, it probably forms a sill-like intrusion. Petrological investigation shows that, though the rock is well jointed,
it exhibits no evidence of gneissic structure or even of the strain-phenomena that are commonly present in the other plutonic rocks of the region. While, therefore, it may be related to the main series of batholithic rocks, it is possible that it belongs to a newer series of intrusions. Turner's (1930) work in the Cascade Valley immediately north of Fiordland has led him to the view that the gabbros and ultrabasic rocks of the Red Hills belong to a later period (early Cretaceous?) than the granite-diorite group of intrusions in Fiord-land, which Hutton and Park (1921) have held to be Palaeozoic, though Speight (1910), followed by the writer, have referred them also tentatively to the early Cretaceous period of orogeny. The norite shows some vague analogies with the rather diverse plutonic rocks of the Bluff and Orepuki, and those closely associated with the granites-granodiorites and diorites in several places in Fiordland. Until more is known of the field-relations of these norites, the age of the Long Sound norite must also remain uncertain.
At the point immediately east of Te Oneroa, on the north-east shore of Otago's Retreat, a sill of ophitic dolerite, thirty feet thick and entirely without sign of strain-effect, invades quartzites against which it shows a fine-grained chilled margin.
The only other intrusive body to be noted here outcrops near the northernmost point of Coal Island as a band of ochreous, porcellanous rock, a few feet in thickness, which has proved to be a much altered lamprophyre, possibly analogous with the Early Tertiary (?) dykes of similar character occurring here and there throughout the Southern Alps.
The Quartz Veins.
The quartz veins fall into several classes:
Veins forming an irregular stockwork following more or less along the strike of the enclosing formation are found either in the quartzites and siliceous greywackes on the one hand, or in the carbonaceous slates on the other. Such veins are specially abundant in the siliceous rocks near fold axes, the country rocks being here often intensely brecciated and riddled with small quartz veins, which are sometimes mineralised. McKay traced one such vein-aggregate through the Golden Site claim on Wilson's River, and another from the western end of Te Oneroa Beach, Otago's Retreat, through the north-eastern portion of Coal Island, where it forms “a network of small veins and leaders of quartz, which abound in pyrites and from which silver-bearing galena has been obtained.” The “carbon slates” of the “Morning Star” Mine and other localities, such as Crayfish Island, contain similar veins.
Quartz veins are less abundant in the crystalline schists and more apt to segregate into irregular masses or “blows.” Such occur locally on the eastern shore of Edwardson Sound near Southport, and in Long Sound. On the southern shore of Cunaris Sound, two narrow veins
were noted running north-west oblique to the general strike and containing, with chlorite and graphite, pyrite and chalcopyrite. Evidences of replacement of the country rock by quartz can be observed.
Veins associated with dislocations of strata may roughly be divided into (c) those associated with flaw-faults and (d) those associated with low-angle thrust-faults. The former occur especially with those fracture-zones that dip at high angles and strike in general east-north-east-west-south-west direction, transecting the more nearly meridional veins. They occur especially near the shores of Preservation Inlet, and are well illustrated by the series of small tear-veins in Cavern Head. In 1863 it was reported that a reef in this region yielded on assay 37 ounces of gold per ton, but it was never rediscovered, and the report, if true, probably referred only to a small ore-shoot. Other vein-filled shatter-zones following the same direction occur in Crayfish Island and near Te Oneroa in Otago's Retreat; the most remarkable of them shows a mass of coarsely crystallised pale buff dolomite containing angular fragments of quartzite. Veins associated with low-angle thrusting are frequent along the shores of Cunaris Sound. The thrust-planes dip gently to the east or west, but the movement in every case is a westward displacement of the hanging wall by a few inches or feet. The planes are often, but not always, marked by quartz in films or layers an inch or more in thickness, sometimes bordered by green mica. Commonly they cut across steeply-dipping veins following the plane of schistosity of the country rock, which they may partly replace.
The occurrence of saddle-reefs is suggested by a “back”* occurring to the east of Powell's Beach, which is in the small bay half a mile east of Te Oneroa, Otago's Retreat.
The tectonic features of the region present many contradictory features, and the problems connected therewith are as yet far from solved. In this section only those tectonic features of the Ordovician sediments, schists, and plutonic rocks are considered, the dislocation of Tertiary rocks being discussed in a later section.
Intensity and Direction of Folding:
There is considerable diversity in the character of the folding, for the intensity of disturbance increases towards the east. On the western coast of Cape Providence the Ordovician rocks form broad,
[Footnote] * “A ‘back’ used here as in Bendigo mining is a bedding plane along which there has been a slipping movement of the beds and a circulation of mineral solutions. It is marked by the presence of flucan or laminated quartz. The cap and legs of the saddle reefs usually form on the backs over the anticlines” (Stillwell, 1917).
open anticlines and synclines with a gentle pitch towards the north-north-east. The promontory itself is apparently divided by a fault, and the rocks on the eastern side dip steeply to the west with a north-north-westerly strike. In Gulches Peninsula and from the southern parts of Preservation Inlet across Cunaris Sound to the head of Edwardson Sound, the rocks lie steeply dipping, arranged in a succession of closely folded anticlines and synclines, and are often so nearly vertical that the fold-axes cannot be distinguished. It is noticeable, however, that the westerly dips are often less steep than those directed to the east, indicating that the folding tends to be asymmetric with axial planes overturned eastwards (see Plate 43). The strike-direction is rather sinuous; in the main, slightly west of true north, it is occasionally a little east of that direction, and, south of the entrance to Cunaris Sound, swings into a north-east direction for a couple of miles, returning to its more nearly meridional trend north of that sound. Possibly the strike of the schists near Blind Entrance, Northport, and the direction of the pitching fold-axes on Cape Providence may reflect this broad inflection of the general line of strike. In the middle parts of Long Sound the same features are continued across from Cunaris Sound. Schists dipping almost vertically are widely extended, with a rather sinuous strike running slightly west of true north. Though this curvature of the strike characterises rocks wedged in between two great batholithic masses, it may not be wholly dependent on their intrusion, and was probably in existence before the rise of the magma into the upper levels of the crust, though perhaps this latter was a late effect of the same orogenic movement as caused the folding.
At the head of Long Sound there are the intensely folded rocks of the Long Sound Series overthrust eastwards and with a strike that runs, on the average, rather east of north. Yet, if the correlation of these rocks with the calcareous formations in Dusky Sound holds good, this crumpling must be a local feature only, for it is not observable in the rocks of Dusky Sound according to Professor Park's explicit statement (1888; 1921). The same conclusion follows from the petrographically-supported comparison of the Long Sound Series with the calc-silicate hornfels-schist further west in the same sound at Last Cove and Only Island, and from the lack of any obvious break between rocks of the Last Cove facies and those of the Long Sound Series on the south-eastern shore of the sound, though it must be admitted that the sequence is here interrupted by many igneous intrusions. The evidence, though weak and inconclusive, is cumulative. The local nature of the intense crumpling is therefore accepted as a provisional hypothesis.
(a) Easterly-directed Fault-thrusts:
One of the most striking features in regard to faulting evidenced in the region studied is the Last Cove Fault. This strikes north-west-south-east, and dips beneath the Treble Mountain batholith, showing by the drag of the schists along the footwall that it has
been overthrust to the east (see Text Fig. 3). It has been shown in an earlier section that there is evidence that this batholith dips away to the south-west, underlying the normal Ordovician sediments there, that its contacts along its western side have the features of shallow-depth thermal metamorphism, and that those on its eastern side, by
Last Cove and opposite thereto, have all the characteristics of contact activities at depth in their degree of dynamo-thermal metamorphism. The deduction seems reasonable that the Treble Mountain-Bald Peaks granitic mass is essentially laccolitic in nature, and rose into the crust as a result and accompaniment of easterly-directed thrust in the higher portions of the crust. The intrusion probably occurred during the later stages of the orogeny by which the invaded sediments were folded and regionally metamorphosed, though its actual date is uncertain. Under the compulsion of thrust from the west the deeper sediments appear to have been compacted in tightly pressed folds, whilst those at higher levels at first under a lesser load were thrust into a synclinal forefold, and there crumpled into a mass of small overfolds, such as characterise the Long Sound Series. Thus might arise a differential movement which would be likely to introduce a zone of shearing between the lower and upper series of beds, which would prepare an entry for uprising magma. The granodiorites and their associates of the Long Sound massif would appear to have been injected as a fringe in front of the Treble Mountain-Bald Peaks massif, and to have entered in lit-par-lit injections into the crumpling rocks of the Long Sound Series. Any major batholiths lying still further to the east beyond the head of Long Sound may perhaps be deemed to have risen as a consequence of the same general upward movement of magma within the crust, initiated by thrust towards the east, by which the plutonic complex of Fiordland was built up. When the plutonic activity died down it was followed
by the emission of siliceous solutions depositing in fractures the more or less mineralised quartz veins of the area. This closed the epoch of easterly-directed pressure and magmatic invasion, and prepared the scene for the next or westerly-directed movements.
(b) Westerly-directed Movements:
When these movements began, the region had probably passed from a geosynclinal stage, and with accompanying batholithic invasion had been elevated into a mountain range. Whether as a consequence of down-folding or foundering of blocks to the west or merely of up-arching of the range, necessitating that the earlier pressure from the west be transmitted through deeper layers, a thrust in the reverse or westerly direction now manifested itself at upper levels of the crust as an expansive movement compensatory to the strong compression at lower levels. Its magnitude may not have been great, but of its existence there is abundant evidence. In a large number of localities there appear planes of shearing or thrusting, dipping gently to the east and showing westerly displacement of the hanging walls to the extent of a few feet. Often this is most vividly clear, as when a nearly vertical quartz vein is cut across by such a thrust, and may be illustrated by mention of actual examples.
The easternmost of these is an almost horizontal thrust plane cutting off a wriggling quartz vein in the quartz-schist of the Long Sound Series north of Only Island in Long Sound. In Cliff Cove, at the head of Cunaris Sound, there are a number of low-angle thrust-planes, cutting across the ridge of a sharp anticline, the cap of which is overthrust to the west, as shown by the drag of the beds and the displacement of quartz veins. On the promontory facing the little islet at the entrance to Cliff Cove, a very marked thrust-plane appears dipping gently westward, but showing the westerly movement of the hanging wall very clearly, for the schists on either wall have been dragged, and there is a long, lenticular “horse” of crushed and slickensided rock enclosed between them.
A like feature was noted again nearly four miles further west along the southern shore of Cunaris Sound near a small islet, and there are a number of further examples displayed on the shores of Cunaris Islets. Again, on the shore of Chalky Inlet near Surf Point, the same feature occurs; the dip of the thrust-plane in this case is N.47°E. at a small angle, with westerly overthrust, though near at hand the dip of other westerly overthrust-faults may be as much as 45°. The rocks are, however, here strongly jointed, and the movements have been complicated by small relative displacements along several series of joints.
Fault and Fracture-Systems.
Systems of intersecting faults, shatter-belts, fractures,* and joints have long been regarded as of considerable significance in guiding the development of fiord topography. Attention was, therefore,
[Footnote] * The term “fracture” is here restricted to mean a plane of disruption along which there has been differential movement, but of unimportant amount.
directed to the evidence for the existence of such fracture-systems in the region described herein. It must be recognised, however, that records of the direction of the prominent fractures observed along the shores of any region cannot give a complete knowledge of the fracturing of the whole area. In some formations, often near the margin of granite-masses, there appears to be little definite arrangement of joints or fractures, probably as the result of the complex stresses set up by the processes of intrusion under pressure and of the diverse reaction to continued strain of the solidified igneous rocks and the invaded formations. The effect also of strains acting obliquely on such different rocks as quartzite and mica-schist may also result in complex and irregular fracturing. Further, it is obvious that, if sufficient angular variation be permitted, an infinite range of directions may be grouped into a few main trends. Nevertheless, there does seem to be sufficient evidence to suggest, if not entirely to justify, the grouping of the fractures in the Preservation Inlet region into four or five major systems. The evidence detailed below is entirely structural, but its possible connection with the principal topographic features will be considered in Part II.
(1) Faults, fractures, and joint-planes trending nearly east and west (generally north of east):
This is the most clearly marked series of fractures, and seems in the main to consist of a group of small flaw-faults running perpendicularly to the regional strike and more or less independent of its local sinuosities. The following are noteworthy examples. The quartzite bluffs immediately south-west of Te Oneroa, Otago's Retreat, are cut transversely by several fault-planes dipping steeply to the south-south-east, the northern block being moved eastwards relative to the southern in each determinable case. Fracture-zones trending north of east traverse the Ordovician rocks in Coal and Crayfish Islands. According to McKay, the strike of these rocks in the northern end of the latter island has been bent almost perpendicularly to its normal direction, as if dragged against a strong, eastward-moving flaw-fault. Similar conditions obtain in the western portion of the Cording Islets, and a fracture belonging to this series runs along the northern shore of the largest islet of this group, whilst the displacement of the boundary of the granite north of these islets suggests a fault in this east-west direction. Local deflection of the strike lines can be seen immediately east of Cavern Head, and this promontory itself has been cut by a series of tear-veins following a trend north of east. The strongly-marked jointing in the centre of the granite mass in the southern portion of Long Sound is again in the same direction, as is that of the granite near Only Island in the northern portion of that sound. The strong joints, which traverse Cape Providence and cut off the quartzite stack known as the Sugarloaf, trend almost due east, whilst the jointing of the igneous rocks not far distant on the eastern shores of Landing Bay also run nearly east, as does that of the granite near Mosquito Point in Northport.
(2) Faults, fractures, and joint-planes trending approximately north-east:
These are strongly suggested by many topographic features, but the structural evidence for them is as yet scanty. There is a strong fracture-zone having this trend traversing the granite on the northern side of Long Sound opposite Only Island. In Preservation Inlet the jointing of the rocks on the eastern part of Brokenshore Bay, a fracture-zone traversing the easternmost of the Cording Islets, the fractures and joints that have guided the formation of the great chasm in Cavern Head, and a fracture observed a short distance east of Seek Cove belong to this group. The sluiced surface in Berg's claim at Te Oneroa shows fractures trending north-east, which cut across a strong fracture-zone running south of east and bring about a total displacement of the northern block of fifteen feet to the north-eastwards. The deflection of the plane of schistosity into this direction at the western entrance to Northport may be noted, and parallel thereto is the eastern margin of the Kakapo Range massif furnished by the west coast of Edwardson-Chalky Inlet, along which there is abundant petrological evidence of fracturing and granulation. A series of joints cutting through the Cunaris Islands follow approximately this direction. Finally, the fractures or joint-planes that may have been instrumental in guiding the formation of Otago's Retreat belong to this group.
(3) Faults, fractures, and joint-planes trending west of north:
This series of disjunctive planes is almost perpendicular to that first described and about parallel to the regional strike. It is represented by a set of joints in the granites of the northern part of Long Sound, by a very prominent group of fractures running through the Cording Islets, by the chief quartz-reefs on either side of Otago's Retreat, by a shatter-zone extending through Te Whara to the mainland, and by the Southport and Gulches Faults. The structural evidence for the Southport Fault is seen in the northernmost of the Garden Islets, of which the eastern portion consists of gently-dipping sericitic schists and amphibolite, while the western portion is composed of almost vertical, highly sheared quartz-sericite-chlorite schist with long lenticles of sheared quartz and mylonite. Further south this zone of shearing extends into the jagged reefs in the narrow strait between the gently-dipping sericitic schists of Garden Island to the east and the normal greywacke and argillites of Gulches Peninsula to the west, rocks of such utterly distinct facies as to indicate their separation at an early date by a most powerful fault, with a heavy westerly downthrow. The physiographic suggestion that the sea-cliffs along the west shore of Southport and their scarp-like southeast continuation represent a fault or fault-line scarp, may indicate movement at a much later date in a reverse direction along the same fault. The evidence for the existence of Gulches Fault is detailed below. Its latest movement was certainly subsequent to the formation of the Tertiary rocks, but probably previous to the latest movement of the Southport Fault. Finally, an approximately meridional trend is followed by a very well-marked series of joints in the folded Ordovician sediments north-west of Cape Providence.
(4) North-west-south-east faulting:
The only strongly-marked fault that trends north-west-south-east is the Last Cove Fault, which dips steeply to the south-west at 50° and shows eastward overthrust. It cuts through the selvedge of Treble Mountain granite massif. Well-developed jointing parallel to this trend is displayed by the schists about Lake Cove, at the head of Edwardson Sound.
(5) East-south-east and other fractures:
A small number of fractures run in an east-south-east direction. They include a shatter-zone passing through Berg's claim at Te Oneroa and displacing the northern block to the eastwards, another cutting through the Cording Islets and dipping at 80° northwards, and a third a little south of Stripe Head, north of the entrance to Southport. Joint-planes in the southern side of Passage Island seen from a distance apparently also follow this direction.
A shear-zone exposed on the southern shore of Cunaris Sound opposite the Cunaris Islands runs in a direction east of north. It dips steeply eastward, and is overthrust to the west. This would run perpendicularly to the last group of fractures, but is the only instance observed of a fracture following such a direction.
The Tertiary Rocks.
Fairly detailed accounts of these sediments have been given by previous writers, and the present expedition, therefore, devoted little attention to them. The basal members of the series vary considerably in thickness, and have been described by McKay as conglomerate-breccias associated with arkosic sandstones, with streaks of carbonaceous felspathic sandstone and mudstone. Near Puysegur Point the sandstone is interstratified with quartz conglomerate with subangular pebbles up to an inch in diameter. Hutton (1875) noted the presence of two seams of resinous brown coal up to three feet in thickness between the lighthouse on the extremity of the point and the boat-landing near it, just inside Otago's Retreat. On Coal Island, granite boulders up to thirty inches in diameter occur in the basal conglomerate, whilst the succeeding strata of arkosic sandstones and grit have interstratified carbonaceous layers with pyritic concretions and beds of grey mudstone containing obscure foraminifera. Between Gulches Head and Price's Beach the sediments are conglomeratic with angular or subangular boulders of granite, porphyry, hornfels, or rarely schist up to a foot in diameter, scattered through an arkosic groundmass or aggregated into impersistent layers. Similar rocks also form the northern portion of Chalky Island. These basal beds range from a hundred to six hundred feet in thickness, and are followed by flaggy sandstones with plant remains, which, on Coal Island, are about two hundred and fifty feet thick, and are succeeded by coarse grits and laminated sandstones on which coal seams rest. The seam observed by Hector on Coal Island was barely a foot thick,
while that occurring at the same horizon on Gulches Head was from two to four feet thick, and may be represented also by a seam exposed near the shore west of Seek Cove. The composition of the coal according to analyses by W. Skey (Hutton, 1875; McKay, 1896) is illustrated below.
|(a) and (b)||
Coal Island (av. of three samples).
Puysegur Pt. (av. of three samples).
In general it may be said that the coal is lenticular, and that the probability of any seam continuing for a long distance is small. The coal measures on Coal Island are overlain by clay-shales and sandstones, the total thickness of beds being estimated by Hector as about 1500 feet. Locally, as at the small pocket-beach on the western side of Otago's Retreat, the clay-shales contain a few obscure foraminifera. In Chalky Island the arkosic sandstone is about 3500 feet thick, and is followed by a hard grey marl which merges locally into impure limestone. The calcareous rocks are altogether 1200–1500 feet thick. Intercalated in them are many bands of arkose from a fraction of an inch to several feet in thickness, and layers of more sandy marls with worm-burrows, fucoid markings, and indefinite plant-remains. Several layers of foraminiferal material were observed in the marl, and specimens of this and of the arkose were forwarded to Mr W. J. Parr, of the Department of Mines, Melbourne, who has prepared a detailed account thereof, which will appear later. The writer is indebted to him for various letters from which the following facts are abstracted:—“The marly rock is not very richly foramini-feral, but a number of foraminifera have been found in the arkosic bands also, together with sponge spicules and fragments of polyzoa.
The following foraminifera have been recognised:
Marsipella elongata Norman, rare.
Ammodiscus sp. aff. incertus (d'Orbigny), rare.
Spiroplectammina parallela Cushman, 1.
Textularia sp., 1.
Vulvulina sp. aff. pennatula (Batsch), 1.
Verneuilina sp. aff. bradyi Cushman, 1.
Nodosaria sp. aff. parexilis Cushman and K. C. Stewart, 1.
Nodosaria antipodum Stache, rare.
Melonis pompiloides (Fitchel and Moll.), 1.
Elphidium sp. aff. macellum (Fichtel and Moll.), rare.
Gumbelina sp. cf. globulosa (Ehrenberg), rare.
Bulimina sp. cf. pyrula d'Orbigny, 1.
B. sp., 1.
Bolivina sp. A., rare.
B. sp. B., 1.
Uvigerina sp. aff. interrupta Brady, 1.
Rotalia sp. aff.calcar (d'Orbigny), 1.
Amphistegina sp. aff. lessonii d'Orbigny, common.
Pullenia sphaeroides (d'Orbigny), 1.
Globigerina sp. A., common.
G. sp. B., frequent.
Cibicides refulgens Montfort, common.
C. sp., rare.
Planorbulina sp., rare.
Halkyardia bartrumi sp. nov., common.
Gypsina sp. cf. howchini Chapman, 1.
Carpentaria proteiformis Goes, 1.
In addition to the foraminifera there are siliceous sponge spicules of the genera Spirastrella?, Geodites, Corallistes, Pachastrella, and a Dictyonine hexactinellid. All of these forms have been recorded by Hinde and Holmes (1892) in the paper on the sponges from the Tertiary of Oamaru and also occur living.
The finding of Halkyardia can justly be described as of extraordinary interest, as this genus has hitherto been known only from beds of Eocene age in Dalmatia and at Biarritz. It is there similarly associated with Amphistegina and Carpentaria. Two species have been described, H. ovata (Halkyard) and H. minima (Lebius), the second of which is the nearer to H. bartrumi sp. nov. Judging from the occurrences in Chapman's (1926) monograph on New Zealand foraminifera, and from my own observations, the deposit is probably of Oligocene or Miocene age. In Australia, particularly in the Lower Beds at Muddy Creek, and in the Miocene at Table Cape, Tasmania, we have a similar occurrence of genera and species which are either identical with or closely related to forms which in Europe are confined to the Eocene.”
No trace of mollusca could be found in the rocks forming the eastern cliffs of Chalky Island.
At Gates Harbour, four miles south-east of Puysegur Point, McKay found that chalky limestones rest on concretionary marly shale and soft sandstone overlying the basal coal-bearing conglomerate-breccia. The concretions are often fossiliferous, and in particular contain shells of a large Ostrea. Formations closely comparable to this series occur at Jackson's Bay, as noted by Hector (1863), Cox (1874), and Park (1887). Cox noted the presence of foraminifera in the sandy beds and the limestones, and emphasised the similarity between the gritty beds and those associated with the coal seams at Preservation Inlet. According to the observations of Cox (1878) and the writer, closely analogous basal conglomerates overlain by thick arkosic sandstones occur in the Te Anau depression, and are exposed also in the Eglinton Valley. They are followed by
grey mudstones. Such formations may thus be taken as characteristic of the Tertiary sediments which accumulated around the granite-schist-greywacke complex which is the core of Fiordland. The conditions under which such sediments were laid down would seem to have required the rapid erosion of a region originally of considerable relief, at first without the opportunity for much chemical decomposition. Eastward of Gates Harbour, McKay (1896) recognised the base of the Tertiary beds breeciated granitic material and coarse granitic boulders which had “gravitated down a steep slope.” Else-where the basal beds seem to have been built out as confluent delta-fans with beds of peat forming in interspersed, often brackish lagoons, the angularity and large size of the boulders indicating that the parent streams were short and swift, draining from highlands near at hand, so that accumulation was probably effected rapidly in temporary flushes. When consideration is given to the fact that the area of the adjacent subsiding land mass was being reduced whilst its relief faded, there is reason to believe that the considerable thickness of the finer beds of the Tertiary sequence indicates reduction in rate of subsidence, which might permit longer retention of detritus in the shore zone, and thus facilitate its more complete trituration. This factor would combine with decrease in relief and in stream gradient to allow the accumulation of thick deposits of mudstone and marl following on the bottomset beds of the early stages of deltaic growth.
The high relief of the Fiordland area in early Tertiary times deducible from the nature of the basal members of the Tertiary beds around it, affords an exception to the general low relief inferred by Cotton (1916) for whatever lands were in existence in the New Zealand region at that period.
The Structure and Dislocation of the Tertiary Beds.
Throughout the region described these beds have been thrown into series of undulations apparently referable to two main groups; first, folding along axes running approximately north-west-south-east, and, secondly, on axes almost perpendicular thereto. McKay's (1896) section from Bald Peaks to the mouth of Wilson's River illustrates the fullest development of the first, showing a syncline followed to the south by an anticline near the present coast. The chief synclinal axis seems, however, to run from near Puysegur Point through Chalky Island. These flexures are probably but major corrugations on a general south-westward or seaward slope. Crossing these are the corrugations of the second group, which broadly may be considered as a vast transverse undulation of the abovementioned seaward slope. Its major synclines run through Chalky Island, which has thus a basin structure, and through Coal Island, the south-western coast of which has been cut back so far that its structure is rather that of a gently-warped pitching syncline than of a basin.
Between these lies the Gulches Head Peninsula, the structure of which is complex and not yet fully known. There is apparently a general south-westerly dip in the northern part of the peninsula,
the southerly inclination of which was observed from Chalky Inlet. Residual patches of arkosic sediment rest on the surface of the granite to the east of Gulches Head itself and dip south-east, whilst a group of stacks lying off the south-eastern portion of this head are made up of similar sediments dipping southwards. Taken all together, these beds appear to be on the eastern limb of a southward plunging anticline, of which Gulches Head is the granitic core. This eastern limb is, however, cut by a distributed fault, with the result that the patch of arkose resting on the granite is thrown down eastward by a few closely-spaced faults with a displacement of ten or twenty feet, beyond which the major displacement brings down to sea-level adjacent to the granite a series of carbonaceous mudstones, which lie probably several hundred feet above the base of the Tertiary rocks. The continuation of Gulches Fault northward has not been mapped, but it probably passes through the small bay east of Red Head. The features do not accord with the conception of Gulches Head as merely a pre-Tertiary prominence overlapped by Tertiary sediments.
The eastern headland of Gulches Peninsula has obviously the structure of a southward-pitching anticline, and consists entirely of arkosic grits and conglomerates. Price's Beach lies in a gentle syncline, and is separated by an anticline and another syncline from the assumed prolongation of Southport Fault by the western shore of Seek Bay, all the folds apparently pitching southwards. Apart from such minor undulations, the broad structural plan shows a major corrugation in a north-east-south-west direction, making a broad syncline between Cape Providence and Gulches Head, and another between Gulches Head and Puysegur Point, the head itself being a faulted anticline. These synclines thus occupy the two major indentations of the coast. The development of a series of joints trending to the north-east parallel to one of the dominant series of joints in the basement rocks seems also to have occurred.
The strong warping of the Tertiary sediments here observed is exhibited also by the otherwise analogous sediments of Jackson's Bay (Cox, 1874).
The relation between the coastal dislocation, the jointing, and the evolution of the modern topography calls for detailed discussion, which is reserved for the next part of this report.
Andrews, E. C., 1905. Some interesting facts concerning the Glaciation of South-western New Zealand. Rept. Aust. Assoc. Adv. Science, Vol. X, pp. 189–205.
— 1906. The Ice Flood Hypothesis of the New Zealand Sound Basins. Journ. of Geology, Vol. XIV, pp. 25–54.
— 1907. The Geographic Significance of Floods, with special reference to Ice Action. Proc. Linn. Soc. N.S.W., Vol. XXXIII, pp. 795–834, esp. pi. xlv.
— 1911. Erosion and its Significance. Journ. and Proc. Roy. Soc. N.S.W., Vol. XLV, pp. 116–136.
Blosseville, J. De, 1826. Nouvelles Annales des Voyages, Vol. XXIX, pp. 145–161. Translation with map in R. McNab's “Murihiku” (Whit-combe and Tombs, Dunedin). Third Edn. 1909, pp. 327–340.
Browne, W. R., 1914. The Geology of the Cooma District, N.S.W., Part 1. Journ. and Proc. Roy. Soc. N.S.W., Vol. XLVIII, pp. 172–222.
Cotton, C. A., 1916. The Structure and Later Geological History of New Zealand. Geol. Mag., Dec. VI, Vol. III, pp. 246–7, 314–20.
Chapman, F., 1926. The Cretaceous and Tertiary Foraminifera of New Zealand. Bulletin No. 11 Geol. Survey of New Zealand.
COX, S. H., 1874. Report on the Coal Measures at Jackson's Bay. Rept. Geol. Explorations, 1874–6, pp. 94–95.
— 1878. Report on the Geology of the Te Anau District. Rept. Geol. Expl., 1877–8, p. 110.
Forbes, C., 1855. On the Geology of New Zealand, with Notes on its Carboniferous Formations. Quart. Journ. Geol. Soc., Vol. XI, pp. 521–530.
Gordon, H. A., 1893. Report of an Inspection of the Preservation Inlet, Wilson River Goldfleld. Annual Statement of the Dept. of Mines, pp. 87–90, 127–128.
— 1895. Digest of Newspaper Articles, especially those by Mr Carrick descriptive of the observations of a Prospecting Party in Chalky Inlet, with map. Annual Statement of the Dept. of Mines, pp. 146–150.
Harris, W. J., and Keble, R. A., 1931. Victorian Graptolite Zones with Correlations and Description of Species. Proc. Roy. Soc. Vict., Vol. XLIV n.s, pp. 25–48.
Hail, T. S., 1915. The Occurrence of Lower Ordovician Graptolites in Western Otago. Trans. N.Z. Inst., Vol. XLVII, pp. 410–411.
Hinde, G. J., and Holmes, W. M., 1892. On the Sponge Remains in the Lower Tertiary Strata near Oamaru, Otago, New Zealand. Linn. Soc. Journ. Zoology, Vol. XXIV, pp. 178–262.
Hector, J., 1863. Geological Expedition to the West Coast of Otago. Otago Provincial Gazette No. 274, Nov., 1863. Mostly incorporated in the following:—
— 1864. Expedition to the West Coast of Otago, New Zealand. Journ. Roy. Geog. Soc., Vol. XXXIX, pp. 96–111.
Hutton, F. W., 1875. Report on the Geology and Goldfields of Otago (Mills, Dick and Co., Dunedin), pp. 40–41, 50, 68, 74, 79, 109–110.
— 1889. The Eruptive Rocks of New Zealand. Journ. and Proc. Roy. Soc. N.S.W., Vol. XXIII, pp. 102–156 (p. 123).
— 1899. Corrections in the names of some New Zealand Rocks. Trans. N.Z. Inst., Vol. XXXI, pp. 483–4.
Inspecting Engineer. Annual Statements of the Department of Mines. References to Preservation Inlet as under:—
1893, pp. 87–90, 127–8.
1894, pp. 84–5
1895, pp. 146–150 (map).
1896, pp. 108–111.
1897, pp. 123–4, with map of the claims.
1898, pp. 105–106.
1899, pp. 100–101.
1900, pp. 29–30.
1903, pp. 112–114.
1904, p. 82.
1905, p. 60.
1908, p. 35.
1909, p. 37.
1911, p. 50.
1912, p. 55.
1913, p. 46.
Johnstone, A., 1889. Surveyor's Report on Preservation Inlet. Otago Provincial Gazette, June 9, pp. 117–120.
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Keble, R. A., and Benson, W. N., 1928. Ordovician Graptolites from Northwest Nelson. Trans. N.Z. Inst., Vol. LIX, pp. 840–863.
Linck, F. W., 1896. In McKay, 1896.
Liversidge, A., 1877. Analyses of a Rock Specimen from New Zealand showing Junction between Granite and Slate. Trans. N.Z. Inst., Vol. X, pp. 505–6.
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McKay, A., 1889. On the Geology of Stewart Island and the Tin Deposits of Port Pegasus District. Rept. Geol. Explorations, 1888–9, pp. 74–83.
— 1896. Geology, General Reports, and Special Examinations made during the year 1895–6. Annual Statement of the Department of Mines, C-5, pp. 108–111; C-11, pp. 3–4. Wilson River and Preservation Inlet Goldfield. Ibid., C-11, pp. 31–45, with map. McKenna Brothers' Claim, Gulches Head, Preservation Inlet. Ibid., pp. 45–7.
Marshall, P., 1907. Geological Notes in South-western Otago. Trans. N.Z. Inst., Vol. XLIX, p. 498.
— 1929. Building Stones of New Zealand. N.Z Dept. Scientific and Industrial Research Bull. No. 11, p. 15.
Morgan, P. G., 1927. Minerals and Minerals Substances of New Zealand. Geol. Surv. Bull. No. 32, p. 66.
Park, J., 1887. On the District between the Dart River and Big Bay. Rept. Geol. Exploration, 1887, pp. 121–141 (p. 131).
— 1888. On Mineral Deposits Dusky Sound. Rept. Geol. Explorations, 1888, pp. 9–15.
— 1921. The Geology and Mineral Resources of Western Southland. Bull. No. 23, N.Z. Geol. Survey, pp. 13–25, 33–38.
— 1922. On the Discovery of Graptolites at Cape Providence, Southland. N.Z. Journ. Science and Technology, Vol. V, p. 264.
Preston, T. W., 1929. Plan of Topographic Survey Dusky and Breaksea Sounds. Surveyed January-March, 1929, and dated 6/7/29. Lodged in Lands and Survey Office, Invercargill. Utilised herein by permission of the Surveyor-General.
Reischek, A., 1887. Recent Exploration North of Chalky Sound, West Coast of Otago. Trans. N.Z. Inst., Vol. XX, p. 441, and plate.
— 1930. Yesterdays in Maoriland. Jonathan Cape, London, pp. 248–253.
Speight, R., 1910. The Geology of the West Coast Sounds. Trans. N.Z. Inst., Vol. XLII, pp. 255–26.
Stillwell, F. L., 1917. The Factors Influencing Gold Deposition in the Bendigo Goldfield. Commonwealth of Australia, Advisory Council of Science and Industry Bull. No. 4, p. 11.
Tattam, C. M., 1929. The Metamorphic Rocks of North-east Victoria, Geol. Survey of Victoria Bull. No. 52.
Thomas, D. E., and Keble, R. A., 1933. The Ordovician and Silurian Rocks of the Bulla-Sunbury Area and Discussion of the Sequence of the Melbourne Area. Proc. Roy. Soc. Viet., Vol. XLV, Pt. II, pp. 33–84.
Turner, F. J., 1930. The Metamorphic and Ultrabasic Rocks of the Lower Cascade Valley, South Westland. Trans. N.Z. Inst., Vol. LXI, pp. 170–201.
List Of Illustrations—Part I.
Plate 41.—Block Diagram illustrating the topography of the region about Preservation and Chalky Inlet, drawn approximately to natural scale. Based on official maps supplemented by many photographs and sketches.
Plate 42A.—Lower Ordovician (Lancefieldian) sediments a mile and a-half north-west of Cape Providence, showing their gentle inclination. Topographic evidence of recent slight uplift and raised beach. Bartrum photo.
B.—Crumpled calc-silicate schist of the Long Sound Series on the north shore a mile from the head of Long Sound. Bartrum photo.
Plate 43.—Geological Map of the region about Preservation and Chalky Inlets, together with section drawn to natural scale.
Note.—No definite soundings have yet been made near the axis of Long Sound. The recorded figures indicate that the depths are greater than 55 fathoms. In Cunaris Sound for Roche moutonée read Roche moutonnée.
Text Figure 1.—Lit-par-lit injection of granodiorite into the calc-silicate schists of the Long Sound Series. Observed on the north shore of Long Sound opposite Only Island. Left side S.W., right side N.E.
Text Figure 2.—General map of the south-western portion of Fiordland, illustrating the dominating directions expressed therein, the probable extent of the Coastal Plateau, and the position of the profiles traced in a plate accompanying Part II of this work.
Text Figure 3.—Section across the Last Cove Fault exposed on the north shore of Long Sound.