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.