Main Divisions.--The first evidence of life appears in rocks of Lower Ordovician age, forming a folded belt in the south at Preservation inlet and in the extreme north-west at Collingwood. They comprise graptolitic slates, quartzites and marbles, and are characterized by an Arenig fauna including Tetragraptus, Bryo graptus, Dichograptus and Didymograptus. According to the Geological Survey the metamorphic rocks already referred to form a Pre-Ordovician series below these fossiliferous sediments, but it is to be noted that no clear line of separation between the two series has yet been discovered. An alternative view regards the Ordovician rocks as passing gradually into mica schists, which are invaded, as in Fiordland, by gneissic diorites. The strike of these ancient rocks ranges from west-north-west to north-north east, but is not very different from the associated Ordovician sediments.
Between the Ordovician sediments and the succeeding Silurian series a strong unconformity is probable. The latter are known only in the north-west of the South island, on the Baton river and at Reef ton. The rocks include argillaceous limestones and shales on the Baton river, and a littoral facies of quartzite, greywacke and limestone at Reef ton, both with a Wenlock fauna.
Nothing is known of the geological history of New Zealand between the Upper Silurian and the close of the Palaeozoic period, from which time the stratigraphic record in the islands is particularly complete. Much of the highlands are built up of folded greywackes, slates and some limestone, with a volcanic horizon recognized near the base of this folded series. The whole is divided into a Permian (Maitai) series and a Mesozoic (Ho konui) series. The nature of the junction between the two is still little understood, various authorities claiming a complete con formity, much regression, or marked diastrophism with plutonic (dioritic) intrusions.
In the type locality (Nelson district) the Maitai series (lime stones, shales and slates) contain Platyschisma, Strophalosia, Mar tiniopsis and Spirifer bisulcata, a fauna characteristic of the Per mian beds of eastern Australia. An extensive series of basic breccias (Te Anau series) forms the base of the Maitai series and upon which the fossiliferous sediments rest. The top of the series is formed of greywackes, in places containing annelid tubes (Terebellina). These are referred to a Lower Triassic age. This Permian series has a wide distribution in the South island. The
succeeding events are not clear. Probably there followed a re gression of the sea, succeeded in turn by a transgression when the Hokonui beds were laid down. The base of this series is of Middle Triassic age, these beds being followed by Upper Trias. They include the Carnic, Noric and Rhaetic stages, the sediments being greywackes, limestones, an horizon of basic tuffs (Noric) and Rhaetic plant beds. The sequence or portions of it are recog nized from both the South and North islands.
The Noric beds, characterized by an abundance of Pseudo montis, have a very wide distribution, extending throughout the Southern Alps in Canterbury, along the Hokonui hills, in the Nelson district, and in the Mokau district of North Taranaki. The series extending from the Middle Trias to the Rhaetic is of great thickness, of the order of i o,000 feet. These beds are followed conformably by Jurassic felspathic sandstones, con glomerates, plant beds and some thin coal seams. Liassic, Bajocian and also Upper Jurassic marine faunas have been described. A widespread series of sediments containing Inoceramus occurs in the east of the North island, probably, in part, of Upper Jurassic age, but extending into the Lower Cretaceous. The problemati cal schists of the South island, well developed in the Otago re gion, and referred to as the Otago schists, are perhaps of Meso zoic age, though they have been referred to horizons from the Archaean to the Jurassic. They appear to pass outwards into sediments indistinguishable from Ordovician or Mesozoic strata.
At the close of this sedimentation, in Lower Cretaceous times, a strong orogenic movement supervened, in which the Hokonui system was folded along meridional lines, the earth movements being accompanied by widespread plutonic intrusions throughout the length of New Zealand. The dunite sills of the Dun mountain and the gabbros and norites of North Cape belong to this epoch, as perhaps do also some of the diorites of the south western district of the South island. The intensest folding in the North island is developed in the east ; in the west the flexures become more open and undulating strata predominate. In the Otago region, the Otago schists have recently been interpreted as a flat lying series forming a packet of recumbent folds, the par ticipating rocks being referred to members of the Maitar and Hokonui series.