The Oamaru Formation.

In order not to crowd the small Geological Map attached to this Report with too many tints, I have coloured this formation and the next, or Pareora formation, the same; however, I shall not fail to give a concise description of each, and moreover shall add such characteristic sections that the reader can easily follow me. The Oamaru formation, where best developed, is of considerable thickness and variety in the nature of the rocks of which it is composed. It lies either on the slopes of the Waipara formation conformably or unconformably, as the case may be, or directly upon the younger palæozoic rocks.

Extent.

In the northern portion of the Province it covers a great deal of ground, where it forms Mount Brown, the Deans, Mount McDonald, and a number of well defined peaks as far as Mount Vulcan on the southern banks of the Motenau river, near the sea coast. Some of the calcareous greensands, forming small hills in the Hurunui plains, may also belong to this formation. South of Mount Brown, the Oamaru beds partly surround Mount Grey, where the so-called White Rock quarry is situated amongst them. They continue to the northern banks of the Ashley river, where their traces are lost. We meet them again at the so-called Curiosity Shop, a small outlier surrounded by post-pliocene alluvium and morainic deposits, on the left bank of the page 305Rakaia, six miles below the gorge, and well known to the settlers o£ this Province for years past as a favourable locality for collecting fossils. We find also south of the Rakaia, strata belonging to the same system, where the Taylor branch of the Ashburton enters the plains, and meet with them still more largely developed on both banks of the southern Ashburton, as well as near the sources of the northern Hinds. They also fringe the Canterbury plains from the Orari to the Kakahu, after which they cover a considerable extent of country, from the middle course of the Opihi north to the Otaio south. Another large zone extends along the middle course of the Waihao branches, and along both banks of the lower Waitaki. During the deposition of this formation, the land sank so considerably that we find now within the alpine ranges beds belonging to it, as high as 5000 feet above the present sea-level. Moreover, it is evident that at one time, wherever favourable chances prevailed, deposits belonging to that formation must have been formed all along the eastern slopes of our Alps, because in many spots small outliers (which have escaped the general destruction) belonging to this formation, have been preserved. Of these localities, those of the Esk, in the Broken River basin west of Mount Torlesse, on both sides of Lake Heron, in the River Potts (east of Mount Potts), between the upper Opuha and Opihi, and near the sources of the Hakataramea, are the most important ones. The Oamaru formation seems to be entirely absent from Westland.

Sequence and Character of the Rocks; Position of Strata.

The beds belonging to the Oamaru formation resemble often in sequence and character of the rocks those of the preceding Waipara formation. They in most instances begin also with littoral deposits, and end with calcareous strata, the latter formed in deeper water. In the northern and middle portions of Canterbury earthy carbonaceous deposits are sometimes associated with them, the lowest beds generally consisting of quartzose sands more or less glauconitic; in the southern portion the formation begins usually with white under-clays, upon which one or several seams of Brown coal have been deposited, some of which will be of economic importance in the future. Above these Brown Coal Measures the further sequence of the beds is nearly the same everywhere. In order to make this more obvious, I shall here enumerate the sequence of the beds in some of the principal localities as they follow each other. On the banks of the Waipara the following sequence is exposed to our view.

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On the calcareous greensands repose under the Deans and at Mount Brown, partly conformably and partly unconformably, greyish, and greenish calcareous sands, sometimes glauconitic or argillaceous, sometimes containing small beds of clay marls, the stratification of which is only shown by beds of a harder nature, consisting of a coarse sandstone, which is formed of the same material, bat cemented by a calcareous matrix. When they repose conformably upon the calcareous greensands of the Waipara formation, they dip south-east 15 deg., but sometimes they haye been deposited on the denuded edges of these older beds, when a dip of as much as 71 deg. to the south is not uncommon. These beds, sometimes several hundred feet thick, rarely contain any fossils, however I obtained from them Waldheimia lenticularis, Scalaria lyrata, and Turritella (probably ambulacrum, Sow.), and portions of Turritella gigantea, Cucullæ alta, as well as a cupshaped Bryozoon. They are overlaid by dart bluish sands, generally calcareous, in which Waldheimia sinuata (Hutton) and a small black Pecten are frequently met with. In these sands, thin beds of rusty coloured tufaceous, or brecciated limestone occur, becoming as we ascend the series more and more frequent and of broader dimensions, till we reach the uppermost bed, 30 to 40 feet thick, by which the summit of theDeans andMount Brown, andmore to the north Mount McDonald and Mount Vulcan and their eastern slopes, have been formed. Some of the harder beds consist almost entirely of fragments of shells, others of corals, being in fact a true coralrag; others contain innumerable specimens of a remarkable cup-shaped Bryozoon; others are partly formed of a Selenaria. Waldheimia lenticularis, Pecten Hoclistetteri, and Caratomus nuperus (Hutton), are also very numerous. These upper beds, more to the south-west, alter to a calcareous and glauconitic sandstone, resembling in many respects the Weka Pass stone. The White Rock quarries near the Okuku have been opened-in them. In the Malvern Hills the whole series is missing, and we only meet with it again in the small outlier on the northern bank of the Rakaia, remarkable for its richness in fossils, the beds consisting here of arenaceous strata of little cohesion, often altering to green-sands. They are separated in banks by small layers of fine clay, resembling sometimes Fuller's earth. There are also concretions of these clays in many places which have the appearance of haying filled hollows, in which formerly organic matter was enclosed, such as driftwood. Some of the layers are full of shells, echinodermata, and teeth of fishes; the large cup-shaped bryozoon occurs in numerous specimens, and small pieces of bones are also occasionally found. In page 307the list of fossils which, have been described from this formation the principal species indicated have been found in this locality. Owing to the occurrence of Pecten Hochstetteri and some other fossils from the Weka Pass beds, I formerly thought that the Curiosity Shop beds were of the same age as the Weka Pass stone, but further research, aided by the description of the fossils, has shown that they have to be classed with the Oamaru formation.

More to the south the Oamaru formation appears to take entirely the place of the Waipara formation, unless we assume that some of the isolated Brown coal basins, situated on the banks of the Ashburton and Opihi, belong to the latter. I allude here principally to the beds on the banks of the North Ashburton, near the junction of the Stour with the Ashburton, and to another locality near Lake Heron. The Oamaru formation is of some importance to the Ashburton and Rangitata districts, as it contains large beds of limestone, and other deposits of similar economic value. Although still of considerable extent, we observe only remnants of a well-developed formation, once covering uniformly the whole portions of the lower country, but which, owing to extensive denudation, principally by glacier and fluviatile action, has now disappeared in most localities. The most complete section of these beds is to be observed on the northern banks of the Ashburton between Limestone Bluff and the Two Brothers. It shows that we have before us beds of various character, ranging from deep sea deposits, through others of intermediate character, to shallow water and estuary beds. This section also fixes the time when the submarine eruptions took place, the former channels of which, now filled with basalts, we observe in several localities. The following succession of beds was observed by me, near and at the Limestone Bluff (section No. 1 on plate No. 5), and is here given in descending order:—

No. 1—Limestone, white on the summit of the ridge, in flaggy layers, consisting principally of pieces of shells and corals, and offering splendid material for the limekiln. Strike 290 deg., dip towards east-south-east 55 deg.	about 15feet.
No. 2—Changes into arenaceous limestone, forming thick beds without divisions	about 70 feet
No. 3—Dark brown volcanic tufas, with numerous iapilli of basaltic lava enclosed	about 15 feetpage 308
No. 4—Gradually this tufa becomes harder, formed of stratified layers of brown or dirty green colours, alternating frequently with, each other, and becoming glauconitic towards the bottom	about 20 feet.
No. 5—Being underlaid by tufaceous calcareous sandstone Gradually altering to—	about 40 feet
No. 6—Calcareous greensands, becoming towards the centre almost black, from grains of glauconite	about 30 feet
No. 7—The latter are cut off from the lowest beds by several layers of shell limestone, consisting mostly of fragments of shells, and enclosing specimens of Pectunculus, of a small white Ostrea, and casts of a bivalve (Mesodesma?)	about 10 feet
No. 8—The lowest beds of the whole series are formed of quartzose sands of light colours, and of considerable thickness, which will be valuable for glass-making.

No. 8 reposes on the slopes of much decomposed quartziferous porphyry.

More towards the centre of the section, and near the channel through which issued the submarine eruption, the beds 5 to 8 are missing. Here repose directly upon the palaeozoic rocks, occurring as a small outlier, thick beds of a tufaceous or agglomeratic character. In some localities, such as the Two Brothers, they consist entirely of palagonitetufa of an uniform texture, whilst a little nearer to the centre of eruption the compact dark mass contains numerous fragments of the same rock enclosed, but of a somewhat lighter colour. On the opposite side of the riyer, at the base of Mount Somers, portions of the same beds are extensively developed, but only the higher series are exposed to view. Of these, the district around the so-called Mount Somers caves, amongst other localities, is the most conspicuous and well-known example. The caves owe their formation to a small creek having washed out its way at the junction of the beds Nos. 1 and 2. The palagonite tufas are here the lowest beds visible. The calcareous beds contain a number of fossils, connecting them with those of the Curiosity Shop at the Rakaia. Another outlier of the same series, and proving: that these beds extended once over a considerable portion of the page 309country, is situated at the head of the northern Hinds (the so-called Limestone range), where the same succession of beds was also observed by me. On the southern banks of the Rangitata, at Coal Creek, the succession of the strata is the same, with the exception that the lowest beds are formed of lignite overlaid by greensands.

In advancing still more to the south, the Oamaru formation is largely developed, and gives to the country, by the conformation of the calcareous greensands usually constituting the uppermost beds, its peculiar features, namely, soft outlines where this uppermost bed has not been cut into, and rocky precipices and cliffs along the banks of the rivers and their tributaries. It is easily seen that the Oamaru formation usually conforms to the outlines of the underlying; palasozoic rocks.

The following is the sequence of the beds on the southern banks of the Kakahu:— The lowest bed consists of shales about 10 feet thick, often arenaceous with imperfect impressions of dicotyledonous leaves. In some localities it becomes more argillaceous and is formed of valuable fireclays. A seam of Brown coal of inferior quality, 20 inches thick, and full of concretions of iron pyrites, lies above it, and is capped by 18 feet of shales, after which a similar seam of Brown coal, 17 inches thick, follows—dip east-north-east 15°. Upon it very dark greensands repose, divided in several layers by more calcareous beds in variegated colours, partly green and partly brown. Above them follows a bed of about two inches thick, formed entirely of Turbinolia, then more greensands, 30 to 40 feet thick, upon which a sandy limestone follows containing a number of fossils, amongst them Cucullæa alta, (Sowerby), Pectunculus globosus (Hntton), Turritella ambulacrum (Sowerby), and a number of others which seem to be undescribed, as no mention of them is made in Hutton's catalogue of Tertiary Mollusca of New Zealand. These greensands sometimes contain fossil wood quite honeycombed by toredos. They gradually get lighter and more calcareous, till they are succeeded by chalk marls and calcareous green-sands, of which the upper bed is sometimes full of harder glauconitic concretions, or it is divided by layers of similar composition into smaller banks. Only in the Upper Kakahu, and on the banks of the Waihi, concretions (Septaria), similar to those of the Waipara, are found, accompanied by fine specimens of Ostrea Wuellersdorfi, but hitherto no fossils of any importance have been obtained from them. Finally, I wish to give the general characteristic features of another page 310section, close to the southern boundary of the Province, exposed on the eastern slopes of Elephant Hill, not far from the Waitaki, on the upturned edges of the Waihao formation.

White underlays, 30 to 40 feet thick, form here the lowest bed of the Oamaru formation, then follows, in ascending order, a seam of brown coal, 12 feet thick, dipping 12 degrees to the east by north. This brown coal, of fair quality, is mostly formed of peat vegetation in which a great number of flattened stems and branches are enclosed, generally arranged in distinct layers (Glance coal), the other layers being more dull, and sometimes of a brown colour. Above this seam of coal sharp white quartz sands, about 10 feet thick, lie, which, in descending, gradually run out, and fireclays, about six feet thick, take their place, reposing directly upon the coal. Then follows, a characteristic bed of quartz conglomerate or pebble bed with a highly ferruginous matrix, consisting sometimes of more or less angular pieces of slates, sandstones, and rounded pebbles from the Waihao formation.

This bed varies very much in thickness; in some districts it is only a few inches thick, in others 30 feet. The presence of this conglomerate in many spots all over the ranges, and where the rest of the formation has been thoroughly destroyed, shows convincingly that the Oamaru formation was once of far greater extent. In some Isolated spots it has effectually preserved the lower beds, including the brown coal seams; in others the whole, with the exception of a few fragments of the conglomerate, has been washed away. Quartzsose sands follow, gradually altering to green sands, with Cucullæa, Turritella, Pecten Hochstetteri, Scalaria lyrata, and Waldheimia lenticularis. In their upper portion these sands become so filled with grains of glauconite that the rock looks quite black. They are succeeded by claymarls altering to calcareous greensands. These characteristic rocks are sometimes massive, sometimes divided into banks by layers of a more calcareous nature, the latter standing out as protuberances. In some localities they are quite full of grains of glauconite, in others this mineral is less frequent. Fucoid casts are sometimes common; in other places the whole rock appears to consist almost entirely of minute pieces of corals, echinoderms, and shells.

Principal Fossil Contents.

The following fossils have been collected in this formation. Some of the localities are given:—

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• Mammalia.—Portions of cetacean bones.
• Aves.—Palkeudyptes antarcticus (Huxley), Curiosity Shop, Broken River.
• Reptilia.—Teeth of Crocodilus, sp. Waihao.
• Pisces.—Teeth of Garcharias, Notidanus, Myliobatis, Lamna, Oxyrhina, Zygobatis, Carcharodon, Pycnodus, Pristis, Sargus, and some other genera.

Mollusca.—Class Pteropoda.

Fossils.	Authority.	Localities.
Dentalium conicum	Hutton	Broken River.
Dentalium conicum var.	Hutton	Waihao.
Dentalium tenuis	Hutton	Waihao.
Dentalium giganteum	Sowerby	Waitaki, Waipara.

Class Gasteropoda.

Fossils.	Authority.	Localites.
Pleurotoma sulcata	Hutton	Broken River.
Pleurotoma hebes	Hutton	Waitaki.
Pleurotoma latescens	Hutton	Mount Brown.
Pleurotoma Buchanani	Hutton	Waihao.
Pleurotoma Awamoensis variety	Hutton	Waihao.
Triton minimus	Hutton	Broken River.
Ancillaria hebera.	Hutton	Broken River, Waihao.
Ancillaria Australia (?)	Quoy	Waihao.
Voluta pacifica, var. C	Lamark	Waipara.
Voluta pacifica, elongate	Hutton	Broken River, Waihao.
Voluta pacifica, Kirki	Hutton	Broken River
Mitra Enysii	Hutton	Waihao.
Marginella dubia	Hutton	Broken River.
Marginella ventricosa	Hutton	Broken River.
Natica solida	Sowerby	Common.
Natica solida Zealandica (?)	Quoy	Waihao.
Natica ovata	Hntton	Common.
Lunatia sutularis	Hntton	Waihao.
Scalaria Browni	Zittel	Common.
Scalaria lyrata	Zittel	Common.
Struthiolaria senex	Hutton	Common.
Struthiolaria sp.	Hutton	Kakahu.
Turritella gigantea	Hutton	Common.
Turritella ambulacrum	Hutton	Common.
Cladopoda directa	Hutton	Waihao.
Calyptræa maculata	Hutton	Broken River, Waihao.
Crypta striata	Hutton	Broken River, Waihao.
Cylichna Enysi	Hutton	Broken River
Turbo superbus	Zittel	Broken
Gribbula nitida	Adams	Broken River

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Class Lamellibranchiata.

Fossils.	Authority.	Localities.
Panopæa plicata	Hutton	Common.
Panopæa Worthingtoni	Hutton	Common.
Mactra attenuata	Hutton	Broken River.
Cytheria Enysi	Hutton	Broken River, Lake Heron.
Dosinia subrosea	Gray	Broken River, Lake Heron.
Dosinia magna	Hutton	Broken River, Lake Heron.
Tapes curta	Hutton	Broken River, Lake Heron.
Cardium patulum	Hutton	Waipara, Broken River.
Hemicardia sp.	–	Acheron
Protocardium serum	Hutton	Broken River.
Venericardia media	Hutton	Weka Pass, Waitaki, Acheron.
Lucina divaricata	Lamark	Broken River.
Astarte Australia	Hutton	Kakahu.
Crenella elongata	Hutton	Broken River.
Modiola albicostata	Lamark	Broken River.
Pinna distans (?)	Hutton	Waihao.
Cucullæa Worthingtoni	Hutton	Common.
Cucullæa alta	Sowerby	Common.
Cucullæa attenuata	Hutton	Waihao.
Pectunculus globosus	Hutton	Broken River.
Pectunculus laticostatus	Quoy	Broken River
Leda semiteres	Hutton	Broken River
Limopsis insolita	Sowerby	Broken River
Pecten Williamsonii	Zittel	Common.
Pecten Chathamensis	Hutton	Broken River.
Pecten Fischeri	Zittel	Common.
Pecten venosum	Hutton	Waihao.
Pecten Hochstetteri	Zittel	Common.
Pecten Hectori	Hutton	Broken River.
Pecten Hutchinsonii	Hutton	Common.
Pecten Beethami var. B	Hutton	Waihao.
Pecten athleta	Zittel	Common.
Pecten multiradiata	Hutton	Curiosity Shop.
Lima paleata	Hutton	Curiosity Shop.
Lima paleata bullata	Born	Broken River.
Lima paleata lævigata	Hutton	Opuha.
Placunanomia incisura	Hutton	Rangitata, Mount Brown.

Class Brachiopoda

Fossils.	Authority.	Localities.
Waldheimia lenticularis	Desh.	Common.
Waldheimia concentrica	Hutton	Broken River, Rangitata.
Waldheimia triangulare	Hutton	Waitaki.
Waldheimia sinuata	Hutton	Common.
Waldheimia patagonica	Sowerby	Broken River.
Waldheimia gravida	Suess	Common.
Terebratella Gaulteri	Morris	Curiosity Shop.
Terebratella Suessii	Hutton	Common.
Rhynchonella nigricans	Sowerby	Common.
Rhynchonella squamosa	Hutton	Broken River.

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Class Echinodermata.

Fossils.	Authority.	Localities.
Pentacrinus stellatus	Hutton	Curiosity Shop.
Cidaris, several species fragmentary	—	Common
Echinus Enysi	Hutton	Broken River.
Caratomus nuperus	Hutton	The Deans, Waipara.
Hemipatagus formosus	Zittel	Curiosity Shop.
Hemipatagus tuberculatus	Zittel	Curiosity Shop.
Amphidotus sulcatus	Hutton	Waihao.
Brissiopsis alta	Hutton	Waitaki.
Hemiaster posita	Hutton	Curiosity Shop, Mt. Somers.
Meoma Crawfordi	Hutton	Common.
Meoma tuberculata	Hutton	Broken River.
Schizaster rotundatus	Zittel	Waitaki, Curiosity Shop.

Crustacea.

Fossils.	Authority.	Localities.
Harpactocarcinus tumidus	H. Woodward	Double Corner.

Igneous Rocks.

I have already pointed out that during the deposition of the upper calcareous strata, eruptions of basic rocks have taken place. At the Limestone Bluff, amongst other localities, beds of lapilli and ashes have been formed between these eruptions, on the southern side of the Ashburton. In other localities, these volcanic tufas are represented by palagonite tufa, of which a specimen was analysed by the Chevalier Charles de Hauer, the results showing that it corresponds very well with the analysis of specimens obtained in other countries. ^*

I think that the dykes found at the entrance of the north Ashburton, consisting of a basic (doleritic) rock, at the gorge of the Rakaia, and at the Acheron, where the rock has a more granitoid texture, have been erupted about this time. More to the south, the submarine eruptions have taken place on a still larger scale, of which the dolerite plateau page 314upon the lower end of which the town of Timaru is situated, is the largest remnant. The best section to be obtained of the relations between the dolerites and calcareous rocks, also forming here the uppermost beds of the Oamaru formation, is in Mount Horrible, about 12 miles from Timaru, rising 1138 feet above the sea-level. From here to the sea, the coulées of dolerite can be traced almost without intermission, showing first that they gradually get thinner as we advance towards the coast, and also that their fall is very slight, being for the last seven miles only about 90 feet in the mile, or 1 foot in 58, the inclination indeed being almost imperceptible. Thus one of the streams, which on Mount Horrible, where they appear almost horizontal, is about 50 feet thick dwindles down to four feet near Timaru. The streams consist of a basic rock (Anamesite), porous, and resembling the uppermost beds in the Malvern Hills. Upon tbe calcareous greensand, forming the upper bed of the Oamaru formation, and which is often so rich in carbonate of lime that it can be used for the limekiln, a bed of volcanic tufa reposes, sometimes changing into an agglomerate, after which the first lava-stream appears. Then follow a number of tufaceous beds with some smaller lava streams between them, till the uppermost coulée is reached, having like the lowest one also a thickness of about 50 feet. This anamesitic rock is extensively quarried near Timaru, and forms a valuable building stone for that town. A similar coulée occurs at the Waihi Bush, between the River Waihi and Hae-Hae te Moana creek, both affluents of the Opihi. There also it covers strata of a calcareous nature, belonging to the Oamaru formation. More to the south, no volcanic rocks of any kind are to be observed, but in the greensands underlying the calcareous beds, lapilli of basic lava are not unfrequent. They might have some connection with the volcanic eruptions during which the lava-streams near the Otepopo river in Otago were ejected, and which are found in a similar position. There is thus sufficient evidence that submarine volcanic eruptions were of not unfrequent occurrence in our tertiary seas.

Age and Thickess.

From the nature of the lowest beds of this formation, we must conclude that they were only deposited after the strata forming the Waipara or cretaceo-tertiary series had undergone considerable changes, and a large amount of denudation. Moreover, it is clear that these older marine beds, in many instances, were uplifted from the ocean, and that the newer beds were deposited upon them, either as littoral page 315or even as fresh water deposits; however, there is no doubt that afterwards the country sank again considerably below the sea-level, because beds belonging to this formation can be traced in the Southern Alps to an altitude of 5000 feet, unless we assume that some portion of the ranges underwent greater subsidence and elevation than others, for which, at least on so large a scale, no evidence can hitherto be found. Thus after the cretaceo-tertiary beds had been raised in succession to near or above the sea-level, during which they were so much destroyed that only in favourable localities some portions were preserved, new beds, first of littoral origin, and afterwards, as the country gradually sank, of a more pelagic character, were deposited above them. Of course the beds in question are not quite coeval, although occupying the same relative positions, as it is evident that those strata in the higher regions, or where the sinking of the ground was slower than in other portions of the country, must be of somewhat younger origin, a fact which may in a great measure account for some want of uniformity in their fossil contents. I wish also to point out another difficulty, the solution of which is of considerable importance for the classification of the beds in question. In the greensands of the Kakahu and Waihao a number of fossils have been collected by me, which Captain Hutton places with the Pareora formation, as for instance, Turitella ambulacrum and Pleurotoma Buchanani. These greensands are overlaid by calcareous greensands, with all the characteristic fossils of the Oamaru formation, on the edges of which the Pareora formation reposes unconformably, consequently a careful study of the more extended collections from these beds is needed to settle this point to my satisfaction. Concerning the age, I have already pointed out that it is exceedingly difficult to assign to these beds their exact position, when using for them any European nomenclature. However, as Dr. Zittel and Dr. Stache have both come to the conclusion, after studying carefully the fossils collected in this formation by Professor von Hochstetter, that they ought to be classed with the upper Eocene, I do not see any reason to depart from this opinion; although Captain Hutton, in his Report on the Geology of Otago, is inclined to include them with the lower Miocene. The thickness of the whole series of beds belonging to this formation is very considerable, and might in the average be 1500 to 2000 feet. In conclusion, I wish to say that 1 have adopted Captain Hutton's designation of Oamaru formation for this assemblage of beds, as the first fossils collected and described were derived from that locality.