The Clarentian Rocks.
The Clarentian as defined by me in 1917 comprises all those Notocene rocks in the Middle Clarence Valley lying below the flint-beds at the base of the Amuri limestone. In the neighbourhood of Coverham fossils have
been obtained from almost the bottom to the top of the series, and have been pronounced by Woods (1917) to belong all to one fauna, which he correlates with the Lower Utatur group of India, which is of about the same age as the Upper Gault and Upper Greensand of England—i.e., Albian. Moreover, all other fossils from rocks having the same relative position in both the Middle Clarence and Awatere Valleys are, according to Woods, of similar age, so that the inclusion of all these rocks under one group-name is justified, although the total thickness of the Clarentian at Coverham surpasses the whole of that of the Notocene in places such as the Waipara district, where rocks from Senonian to Pliocene are represented. This is probably due to the fact that the Clarentian deposition followed close on the post-Hokonui orogenic movements, and erosion on a fairly emergent land-mass was still active. Probably also the Coverham area was not far from the mouth of a large river.
The Clarentian rocks, while preserving for the most part the same general character of sandstones and mudstones, vary rapidly from place to place, and there is no single characteristic stratum which can be followed from end to end of the valley. There are, nevertheless, some notable differences in the rocks at the two ends of the valley. The rocks at Cover-ham are dominantly black mudstones with occasional calcareous concretions, divided into three main groups by sandstones, and resting on conglomerates. In the Herring River, and thence nearly to the Bluff River, the sequence commences with terrestrial coal-measures, followed by several lava-flows, and these are succeeded by a marine series of sulphurous mudstones, sandstones with pebble-beds, loose sands, and glauconitic sandstones.
Coverham (Plate XXV, fig. 1).—I have suggested the following division of the sequence at Coverham (Woods, 1917, p. 2), but it must be clearly understood that this classification has a strictly local application:—
|Sawpit Gully mudstones||3,200|
|Nidd sandstones and mudstones||550|
|Cover Creek mudstones||2,000|
|Wharf Gorge sandstones||450|
The conglomerates were examined in a tributary of the Wharf Stream coming from the Sawtooth Range, where they strike at the base N. 40° E., dipping at 45° to the north-west, and near the top strike N. 60° E., with dip 60° to north-west. The underlying pre-Notocene greywackes and argillites strike N. 20° W., with a steep dip to the north-east. The unconformity is well exposed in section (Plate XXV, fig. 2). The conglomerates are, in part, of a peculiar character, not uncommon elsewhere in the Clarentian—viz., that they consist of well-rounded pebbles, a few inches in diameter, of hard rocks such as quartzite, set in a matrix of mudstone. The conglomerate series at this point commences with beds of hard conglomerate alternating with this pebbly mudstone, then some layers of pure mudstone, and then more bands of pebbly mudstone, the whole being about 250 ft. in thickness. The conglomerate consists mainly of well-smoothed ellipsoidal pebbles of hard sandstone and quartzite, up to 8 in. long, but mostly with a major diameter of 3 in. to 4 in., with only a few pebbles of mudstone and soft sandstone near the base. Green and liver-coloured quartzites are relatively rare, but white quartz and bright-red and pink
jasperoid quartz are common. Granites and porphyries are only occasionally seen, while dark crystalline rocks appear to be absent. No schist or limestone pebbles were observed. The conglomerates were not followed along their outcrop. They cross the Ouse Stream about a quarter of a mile below the junction of the Wharf as a narrow band of pebbly mudstone only 5–10 ft. thick. As already mentioned, there are two thick bands of conglomerate farther down the Ouse which may possibly be Clarentian.
The Wharf mudstones form both banks of the Wharf Stream between the gorge and the crossing of the pack-track, above which the strike becomes more easterly, and the beds continue into the upper Wharf. The rocks are mainly dark micaceous mudstones without many concretions, and near the junction of the tributary above mentioned yield finely-preserved specimens of Belemnites superstes Hector. Near the crossing of the pack-track sandy beds are crowded with the shells of a large depressed Inoceramus, and lower down the creek the mudstones contain Aucellina euglypha and Belemnites superstes. No observations of strike and dip were made, except that in one place on the left side there is a reversal of dip. In the upper Wharf, what are presumably the Wharf beds consist predominatingly of mudstones containing large Inocerami, with occasional bands of harder sandstone, forming waterfalls, and thin bands of pebbly mudstone. The beds are thrown into a series of folds, so that a clear section was not observed. The mudstones, however, are very thick. The Wharf beds were again observed in the Ouse, about 200 yards below the junction of the Wharf, in a large cliff on the right-hand side consisting of thin-bedded sandstones and mudstones. The sandstones contain coaly plant-remains, and one block with shell-fragments was obtained, which contained a plicate ostreid shell, part of the dorsal valve of a Terebratellid (the only brachiopod yet obtained from the Clarentian), and a small piece of the test and some minute spines of an echinoid. A concretion picked up at this point contained a gasteropod and a Dentalium, and is in the hands of Professor Wilckens, of Jena, for identification.
Still farther down the Ouse, the lowest Wharf beds consist of hard mudstones crowded with a large flat Inoceramus, and are the cause of small waterfalls on tributaries coming in on each side (cf. Cotton, 1913, fig. 14). No specimens suitable for identification could be extracted, but pieces 9 in. in length were obtained, and the whole shell must be over 1 ft. in length.
McKay's description of the Wharf beds is as follows: “The lowest rocks, as conglomerates, are rather suddenly succeeded by black slaty, marly beds, containing concretions of cone-in-cone limestone, and sandstone bars full of Inoceramus, and here and there a belemnite and other fossils characteristic of the Amuri series.”
The Wharf Gorge sandstones and mudstones occupy a width of about a quarter of a mile in the Wharf Gorge, which crosses them transversely to the strike, and in the lower part of the Cover Stream. The rocks are dominantly sandstones, in beds 6 ft. thick below and 3 ft. above, and are parted by thin beds of mudstone. The sandstones in the upper part are fissile and slightly micaceous, and contain poorly preserved plant-remains, principally fossil wood, and occasionally the cast of a belemnite. The strike in the lower end of the gorge is E. 10° dip 63° to the north. The Wharf Gorge beds extends in an east-north-east direction into the ridge between the Wharf and Cover Streams, but are not there well exposed for study. Where they cross the Ouse the sandstones are not so well
developed. They have here a strike of N. 60° E. and dip 45° to the north-west in the lower part, and a strike of N 70° E., and dip 56° to the north-north-west at the junction of the Ouse and Nidd.
McKay describes the Wharf Gorge beds as follows: “The higher beds [i.e., higher than the Wharf beds] are thick bedded sandstones of a grey colour, light-grey or yellow when weathered, parted by thinner beds of black slaty shale.”
The Cover Creek mudstones are black micaceous mudstones with numerous small irregular calcareous concretions which are more generally fossiliferous than those of other divisions of the Clarentian. Belemnites and occasionally specimens of Inoceramus are also found embedded directly in the mudstones without being surrounded by concretions. There are a few occasional beds of sandstone. The beds below the house at Coverham strike N. 60° E., with dip 55° to the north-west. A little farther up the Cover Creek the strike turns more to the north. The beds cross the lower Nidd and are exposed in the lower Swale, where they have the same characters but are less fossiliferous. The best locality for fossils lies in Cover Creek, about 200 yards above the old sheep-dip. Here were obtained the ammonite Turrilites circumtaeniatus, Belemnites superstes, Inoceramus concentricus, the carapace of a crab, a small compound coral, the skeleton of a fish, numerous fish-scales, and specimens of fossil wood. McKay's description of the Cover Creek and higher beds is as follows: “These beds [the Wharf Gorge sandstones] are followed by softer, more argillaceous or marly strata, until reaching a bed of sandstone, which yields the fossils of the black grit, and thus the sequence of the Amuri series is here somewhat arbitrarily brought to a close…. The black grit … as a calcareous sandstone contains ammonites, Inoceramus, fish-scales, and numerous leaves of a plant common enough in the underlying Buller series…. At Coverham, from the horizon of the black grit to the flint-beds underlying the Amuri limestone, there is an enormous development of black micaceous clay-marls, divided into two parts by a band of grey or brown sandstones containing plant-remains. These beds are crowded with calcareous concretions, and, especially in the higher beds, contain Inoceramus in great numbers.”
Unfortunately the collections preserved by McKay from Coverham were disappointingly small and poor, and the ammonite mentioned above was not amongst them. There is a little uncertainty which is the bed he called the black grit, but it is probably a sandstone in the Cover Creek beds opposite the house, which lies 50–100 ft. below the horizon where Turrilites circumtaeniatus was obtained, and which can be traced into the Nidd.
The Nidd sandstones and mudstones cross the Nidd obliquely above the junction of Sawpit Gully with a strike of N. 60° E. and a dip of 55° to the north-north-west, and they cross Sawpit Gully near the bottom. They consist of sandstones with a greenish tinge, 1 ft. to 2 ft. in thickness, separated by 6 ft. to 20 ft. of mudstones. Both sandstones and mudstones contain in abundance a large Inoceramus. They are followed, up the Nidd, by sandy mudstones which become flinty above, and contract the valley to a gorge. The mudstones contain a considerable amount of pyrites and exhibit a yellow efflorescence. The flint-beds seem to widen in outcrop to the east in the ridge between the Nidd and the upper Cover, where they form a promment strike ridge. A little to the south there is a parallel strike ridge, apparently formed by the lower sandstones. The
flint-beds do not seem to persist to the west into the Swale, but about a mile and a half above the junction with the Ouse there is a series of handed sandstones and mudstones, striking east-north-east, and dipping 40° to the north-north-west, which probably represents the lower sandstones.
The Sawpit Gully mudstones are clearly exposed in the steep bed of Sawpit Gully (Plate XXVI, fig. 1), and consist predominantly of black mudstones, but occasional thin beds of sandstone are found. There is some folding in the section, but, on the whole, the dip is to the north-north-west, like that of the overlying flints and limestones. Calcareous concretions up to 1 ft. in diameter are common in the upper 400ft., but below that they are rarer. In the uppermost 15 ft. pyritous nodules are abundant, but they do not persist far downwards. At the actual junction with the flint-beds there is a strong yellow efflorescence. The junction appears to be quite conformable. Inoceramus concentricus var. porrectus was obtained 20 ft. below the junction and also at about 100 ft. The ammonite Gaudryceras sayci was obtained in a large concretion about 300 ft. below the junction.
The Sawpit Gully beds are exposed in the Nidd above the flint gorge, where the valley again opens out in the softer rocks. Near the base there is a band of sandstones and sandy mudstones containing a large species of Inoceramus. The higher beds are fine-grained black mudstones with small concretions, in which fragments of crustaceans were observed.
In the Swale, owing to slips and talus slopes, there is not a continuous exposure of the Sawpit Gully beds. Not far from the top there is some sharp folding of the beds, causing local reversals in the direction of the dip (Plate XXVI, fig. 2). From the highest exposure concretions containing numerous specimens of Aucellina euglypha and fossil wood and plantimpressions were obtained.
The thicknesses given above for the various divisions of the Clarentian at Coverham were estimated, except in the case of the conglomerates, by measurements from a section drawn to true scale. An average dip of 55° was allowed, but it will be observed that the dip is often steeper and seldom less than that figure. The reversals of dip due to folding are unimportant, but have been allowed for. An almost continuous section of the beds has been observed, and no faults of any consequence were seen. Consequently, unless there is a very strong unconformity between the Clarentian and the Amuri limestone and a repetition of the beds by closely appressed folds, there is no escape from the conclusion that the thickness given is approximately correct. Hector and McKay agree in estimating the total thickness up to the “grey marls” as approximately 12,000 ft. Woods remarks that the thickness, if correctly estimated, is very great in view of the unity of the molluscan fauna.
The beds are marine throughout, and calcareous concretions are abundant, but plant-remains and fossil wood are found in the sandstones and concretions from top to bottom. The black colour also of the mudstones and sandy mudstones is doubtless due to the presence of carbonaceous matter. Glauconite has been observed only in the greenish sandstones of the Nidd beds. The above facts, together with the rapid lateral variation in the sandstones and the presence of the pebbly mudstones in the lower beds, suggest that the whole series was deposited as the topset beds of a continental shelf undergoing rapid depression and near the mouth of a large river, the sands and gravels of which were arrested nearer shore or up the estuary by its drowning.
Hector's subdivision of the beds from Coverham to the Mead Gorge is as follows:—
Contorted sandstones (Belemnites superstes); volcanic dykes.
Concretionary marls; large Inoceramus.
Sandstone with plants.
Septaria clays, with Inoceramus, belemnites, and Conchothya.
Black grit with fish-scales, ammonites, Inoceramus.
Black marls with sandstone bands.
Plant-sandstones with Dentalium majus, Nerita, Natia, Inoceramus (= Amuri sands).
Black marls with cone-in-cone limestone bauds.
Conglomerates and brown sandstones containing plants and coal.
In attempting to establish a similarity with the Piripauan beds at Amuri Bluff, Hector has given in the above succession too much prominence to the sandstone bands and too little to the black mudstones which make up about 90 per cent. of the succession. The green sandstones mentioned were probably observed on the Kekerangu side of the pack-track from that place to Coverham, where such beds occur.
The Clarentian near Coverham is occasionally penetrated by intrusive rocks which consist of very much weathered amygdaloidal basalts. A dyke trending E. 15° S., nearly vertical but with a slight inclination to the north, appears in the north-east bank of the Swale about a mile above its junction with the Nidd. A similar, somewhat thicker dyke, but possibly the same, outcrops a quarter of a mile farther up-stream. McKay describes a dyke in the Wharf as separating the upper and lower beds—i.e., a sill. It is of similar petrological character, and is either a sill or else a dyke truncating the beds very obliquely. These intrusives are similar to one penetrating the Amuri limestone in the Kekerangu River, and are probably to be correlated in age with the volcanic rocks overlying the Amuri limestone in the Ure Valley and in the Herring River.
Isolated Hill Creek, Ure Valley.—From the Chalk Range the Amuri limestone swings round in a great curve to Benmore, and the underlying Clarentian beds follow suit, but owing to the inaccessibility of this heavily forested and deeply gorged country they have been examined only in the Isolated Hill Creek, a tributary of the Ure River which, cuts through the limestones and flints in a gorge between Isolated Hill and the spurs of Benmore. At the top of the gorge the strike of the flint-beds and underlying Clarentian is east-north-east, with dip 36° to the north-north-west. About 1,500 ft. of Clarentian beds are exposed, consisting of dark-grey indurated mudstones or sandy mudstones, rapidly disintegrating into small angular fragments on exposure. Concretions of all sizes up to 7 in. diameter occur sparingly thoughout, but are rarely fossiliferous. One large ammonite was obtained in a concretion from the stream-gravels, but was declared by Mr. H. Woods to be indeterminable. The beds terminate downwards against a fault which has brought down the Whern-side block of Amuri limestone and flint-beds against the Clarentian.
The junction between the Clarentian beds and the overlying flint-beds appears not only to be perfectly conformable, but to exhibit a passage between the two formations. It is described in detail below.
Upper Ure Valley.—The Notocene rocks in the upper Ure and upper Swale Valleys form a great overturned syncline, truncated by the great
Clarence fault and its branches. Where on the upper side of the syncline the sequence is reversed, a small thickness of Clarentian beds lies above the flint-beds, between them and the fault-line. These were observed in the large tributary of the Ure River entering it in a south-east direction from Blue Mountain. About 100 ft. of Clarentian beds are here exposed, consisting of micaceous mudstones weathering purple-grey with a yellow efflorescence on joint-planes. They have the same strike as the underlying flint-beds—viz., north-east—with a dip of about 50° to the north-west—i.e., towards the fault-line. A large concretion lying in the creek at this point was observed to be crowded with fibrous fragments of Inoceramus. There appears to be perfect conformity with the flint-beds. The actual fault-line is obscured by slips.
In a tributary of the above creek, entering if from the north-east along the fault-line, some decomposed amygdaloidal basic volcanic rocks were seen to the north-west of the flint-beds, and are therefore probably in the Clarentian series.
Middle Ure Valley. — Pebbly mudstones were observed in the Blue Mountain Creek at the apparent top of a series of hard sandstones and thin-bedded mudstones apparently overlying the Amuri limestone or Weka Pass stone, which is here not more than 150 ft. thick, and strikes in a north-easterly direction, dipping north-west. Probably the series is overturned and the succession reversed at this point, as it is higher up the Ure Valley. The conglomerates contain fragments of Inoceramus and pebbles of dark limestone (itself containing Inoceramus), besides white quartz and red jasper. A fault crosses the creek about two miles up, and above this, in a branch running to the Blue Mountain, the Clarentian rocks appear to be repeated. There is a succession of hard sandstones with occasional shaly beds, both containing occasional plant fossils, and thin pebbly mudstones containing Inoceramus fibres. There are many repetitions of the pebbly mudstones in the creek. Many small dark finegrained dykes were observed intersecting the sandstones.
Lower Ure Valley.—Clarentian rocks are probably well developed in the hills to the north of the lower Ure, where thin bands of Amuri limestone appear, but exposures are not good and the sequence has not been clearly ascertained. Not far above the crossing of the coach-road a syncline of limestone occurs, underlain by sandstones and mudstones containing Inoceramus. The limestone crosses the hills obliquely and terminates against the Awatere beds, probably in a fault-line, and the beds farther up the hills to the west are therefore probably Clarentian. They consist mainly of sandstones, but the top of Hungry Hill is composed of volcanic breccia, which may be Clarentian. McKay correlates it with the Flaxbourne breccias, which lie at the base of the Clarentian series in the Ward district
Mead River.—McKay describes the Clarentian rocks exposed in the Mead River as follows: “In the Mead, the conglomerates at the base of the Amuri series are finely exposed. The succeeding beds are grey sandstones and darker shales thrown into a great number of undulations, which are flat and shallow, or more frequently sharply caught up at high angles, and are often crushed and contorted in a most extraordinary manner. Here beds of this character continue without means of distinction upwards into the Waipara formation, and, scarcely altered in character, reach to the under-surface of the great flint-beds that underlie the Amuri limestone.”
To this description I have little to add. No recognizable fossils have been obtained from the Clarentian beds in either the Dee or the Mead, and consequently the beds have not been closely studied. The series appears to be considerably thinner than at Coverham, but the thickness is difficult to estimate owing to the contortions near the base. There is also some sharp folding near the top, and the beds run nearly horizontally for some distance. Before reaching the flint-beds, however, they once more assume the dip of these. The actual junction is not exposed.
Limburne Stream.—The series commences with pebbly mudstone, hard sandstone, and a second pebbly mudstone, all striking nearly east and west, and dipping to the north. The succeeding beds are a series of thin-bedded sandstones and mudstones. No fossils were obtained, and the junction with the flint-beds could not be observed.
Dee River.—The Clarentian rocks are not well exposed on the banks of the Dee River, and have yielded no fossils except fragments of Inoceramus. The series commences with a pebbly mudstone followed by a hard sandstone. Higher up the beds appear to be mudstones and thin-bedded sandstones with few or no concretions. The total thickness appears to be much less than that at Coverham.
Branch, Dart, and Muzzle Rivers.—For this part of the district we must rely solely on McKay's observations. He states that the lower part of the Clarentian (so-called Amuri series) is essentially the same as in the Mead and the Dee. The upper part in the Dart River, for some distance below the commencement of the limestone, consist of “grey sandstones and soft, crumbling sandy beds of dark colour, with small calcareous concretions containing Inoceramus, and small spheroidal concretions of ironpyrites…. In the Muzzle the beds are highly-contorted sandstones and sandy or marly shales containing, near the under-surface of the Amuri limestone, saurian concretions of enormous size, one specimen of which, yet in situ on the east bank of the left branch of the river, is about 14 ft. in diameter.” The name of “saurian concretion” was given from a mistaken correlation with the saurian beds of the Piripauan.
Bluff River.—There are two outcrops of Notocene rocks in the Clarence Valley near the Bluff River, separated by an anticlinal core of pre-Notocene rocks. The north-western outcrop is similar in its structural relations to those already described from Coverham to the Muzzle River, and is continuous with them. The south-eastern outcrop will be described later.
In the Bluff River the Clarentian rocks are not well exposed, owing to slips on the banks, and I was unable to observe certain beds evidently exposed when McKay examined the section. The lowest beds I observed were about 600 ft. of thick-bedded mudstones and sandstones, with a dip to the south-east—i.e., away from the limestone. Higher up the river there are sandstones on the west bank with a normal dip—viz., 75° to the north-west—the strike being N. 50° E.
McKay describes the succession as he observed it as follows: “The lower beds of the Amuri series are for a short distance obscured along both banks of the river Rocks belonging to the younger series first show on the south-west bank of the river as banded sandstones with shaly beds between. These are overlain by sandstones and conglomerates, some of the conglomerates containing fragments of a large Inoceramus and great numbers of a large form of Trigonia…. Belemnites, usually as fragments, are also found in these conglomerates. The sandstones are almost destitute of fossils. To the north-west, and higher in the section, these beds are
followed by dark sandy beds with concretions, the outer part of which consists of cone-in-cone limestone; and these are succeeded by the Amuri limestone.”
Gentle Annie Stream.—The Notocene beds continue from the Bluff River into the Gentle Annie Stream, where the Amuri limestone occurs in a syncline. The Clarentian beds below the limestone to the south-east are not well exposed, but the presence of muddy sandstones dipping to the north-west was observed.
Herring (or Seymour) River.—The exposures of Clarentian rocks described from Isolated Hill Creek, Coverham, and the Mead to the Gentle Annie all belong to a continuous strip forming the lower member of the Notocene rocks involved in the great Clarence fault. From Bluff Hill to the Gore River there are other outcrops of Notocene rocks involved along the more north-easterly parallel faults, except for the large outcrop between Bluff Hill and Limestone Hill, which seems to occupy a synclinal depression. Many of these outcrops include only Clarentian rocks, while in others a nearly complete succession of the Notocene is included. The Clarentian rocks in this area commonly commence with terrestrial coal-measures, and volcanic rocks are well developed. The most complete and typical succession is that of the Herring River, which will be considered first, although it disturbs the geographical sequence of the account.
In the lower Herring River the unconformity of the Clarentian and pre-Notocene rocks is well exposed. The latter consist of concretionary (“cannon-ball”) sandstones and thin argillite bands, striking N. 15° W., with a very steep dip to the west. The Clarentian rocks strike, at the base, N. 30° E., and dip 44° to the north-west—i.e., down-stream. The Notocene series is folded into a syncline and anticline before reaching the Quail Flat fault-line near the junction with the Clarence River, and the syncline brings the Amuri limestone down to the river-level, thus separating two exposures of the higher part of the Clarentian beds.
The lowest rocks are coal-measures, 50 ft. thick, forming cliffs of a reddish colour. The series commences with a seam of lignite a few feet thick, followed by carbonaceous shales, grits, sands, and ferruginous sandstones, with thin seams of lignite. Some of the sandstones and shales are crowded with plant fossils. Then follows a series of volcanic rocks about 320–340 ft. in thickness. Four well-marked lava-flows can be recognized, but there may be more. The rocks have not been examined microscopically, but appear to be olivine basalts. The lowest lava is not columnar, and is 60–70 ft. thick, and it is suceeded by more coal-measures, varying from 7 ft. to 15 ft. in thickness. The second flow, which is coarsely porphy-ritic, is columnar for the lower 20 ft., passing into breccia for the upper 20 ft. The third flow of fine-grained basalt is 15 ft. thick, and is columnar throughout. The fourth flow lies 150 ft. farther up, and is about 50 ft. thick. The outcrops of the interbedded rocks at river-level are covered by basalt screes, but may be exposed on the higher slopes of the valley-sides. The fourth lava is immediately followed by mudstones.
Farther down the stream the section of the succeeding Clarentian beds is far from continuous, as the banks on each side are much slipped, probably owing to the predominance of loose sandy beds. Such rocks as are exposed are mudstones, sandstones, sometimes with pebble-beds, and a thick series of mudstones with yellow efflorescence in beds about 1 ft. thick, alternating with soft sandstones in beds of 18 in. to 2 ft. thick. Higher up in the succession the mudstones become more massive and the
sandstone intercalations disappear. Altogether there are probably over 1,000 ft. of strata between the top of the lava and the base of the Amuri limestone. The uppermost 60 ft. consists below of 20 ft. of pale-green sandstone, passing up into bright-green glauconitic sandstone, and finally into hard glauconitic limestone. There is some appearance of unconformity in the overlying Amuri limestone cf. p. 328).
In the north-west wing of the anticline farther down the river the lowest beds seen are about 200 ft. of sulphur mudstones. These are succeeded by about 50 ft. of sulphur sands, of which the upper 15 ft. is glauconitic.
Fig. 5.—Junction of Clarentian and Amuri limestone, north-west wing of anticline, Herring River. a, Amuri limestone; b, glauconitic sandstone; c, mudstone; d, brown glauconitic sandstone; e, green glauconitic sandstones; f, sulphur sands.
The latter bed is apparently truncated at a gentle angle and overlain unconformably by a thin bed of mudstone, which in turn is followed conformably by a glauconitic sandstone, 10 ft. thick, and that by the Amuri limestone. The cliff in which this section is exposed cannot be scaled, and the ground slopes away steeply at the bottom, so that it was difficult to be certain of the unconformity.
McKay recognized only two “great sheets” of volcanic rock, and made a collection of fossils from sandstones and pebble-beds resting on the upper surface of the second sheet. The fossils determined by Woods were Arca (Barbatia) sp., Trigonia glyptica, T. meridana, Modiola kaikourensis, Belemnites superstes. I did not recognize this bed, but a little way down the river from the uppermost lava I picked up in the river-gravel a boulder of conglomerate containing Trigonia glyptica.
The upper beds are described by McKay as “soft grey sandstones, and black, sandy, sulphurous, micaceous beds, with cone-in-cone concretions, overlaid by greensands, which, associated with thin beds of volcanic
rock (on the north-east bank of the river only), underlie the Amuri limestone.” These upper beds of volcanic rock I did not observe.
Quail Flat.—The Quail Flat fault runs from the mouth of the Herring River for some distance along the bed of the Clarence River, then enters the southern bank to pass though Quail Flat, crosses the river again at the southern end, passes through two southerly projections of the north bank, and finally again enters the north bank to run behind Red Hill, where its presence was inferred by McKay. The base of the Notocene rocks must be considerably folded longitudinally along this line, since at Quail Flat and farther north-east only lower Clarentian rocks are involved at approximately the same height as that at which the Weka Pass stone occurs only two miles to the south-west.
The Clarentian rocks are exposed on the southern bank of the Clarence River near the upper and lower ends of Quail Flat, the intervening spaces on the bank being occupied by pre-Notocene rocks. At the upper end of the terrace the pre-Notocene rocks for some hundreds of yards are greywackes and thin-bedded argillites striking N. 30° W. and dipping nearly vertically. Farther up the river conglomerates appear, the line of junction striking N. 65° E., and dipping apparently vertically. The conglomerates consist mainly of rather decomposed. well-rounded basalt pebbles, with a greasy matrix recalling the fossiliferous tuff of Limestone Creek, Awatere Valley. They contain pieces of carbonized fossil wood. Up the river these are succeeded by coal-measures striking north-east, dipping 58° to the north-west, and consisting of thin-bedded mudstones, carbonaceous shales, and sandstones, with elliptical masses of ferruginous sandstone. These rocks strike south-west into a projection of the terracebank, and the continuation of the succession is then obscured for about 100 yards. At the end of the projection a volcanic rock appears, and this is followed by a succession of greasy conglomerates and coal-measures similar to the last. It seems probable that the junction between the first-described conglomerate and the pre-Notocene rocks is a fault.
McKay's description of this outcrop is more detailed, and he mentions no break in the succession. The first-mentioned exposure of coal-measures he describes as followed by thick beds of volcanic rock, divided by tufas, conglomerates, and shales, the highest stream of volcanic rock being followed by conglomerates, grits, sandstones, &c. From the beds between the first and second volcanic rocks he obtained leaf-fossils and fresh-water shells, and underneath the higher stream some very fine specimens of dicotyledonous leaves.
At the lower (down-stream) end of Quail Flat the pre-Notocene rocks are concretionary (“cannon-ball”) sandstones with thin argillite bands, striking N. 20° E., and dipping 40° to the east-south-east at the lower junction with the Clarentian rocks. The latter series commences with mudstones and lignite seams, striking N. 20° E., and dipping 60° to the west-north-west. The higher beds, exposed up-stream, are sandstones, followed by more lignites. Higher up the succession is obscured by slips, but pre-Notocene rocks appear in cliffs 200 yards farther up the river, so that presumably the fault-line closing the sequence here enters the river-terrace.
This exposure was evidently much clearer at the time of McKay's visit, for he describes a number of beds I did not observe. “At the eastern end of the section the lowest bed is a soft greensandstone, which is followed by grey sandstones, with irregular beds of coaly shale. These latter beds
contain elliptic masses and irregular bands of ironstone, which are full of plant-remains. A very large dicotyledonous leaf, with Dammara leaves, Taeniopteris, &c., occur in the ironstones and in the sandstones and sandy shales which overlie the lower beds. Casts of trees 18 in. to 2 ft. in diameter lie at the foot of the cliff along the river-bank, and these can be seen in situ surrounded by a thin layer of bright coal. Hard calcareous sandstones overlie these beds, with which are layers of ironstone, and in these beds dicotyledonous leaves and large specimens of Taeniopteris are abundant. About 100 ft. from the lowest beds of the series fine splintery black shales are crowded with long slender leaves having parallel venation; and in these beds and a greensandstone band parting them into an upper and lower division fresh-water shells, as casts of Cyclas and one or two species of univalves, are found in great abundance. Fine-grained grey and gritty sandstone follows, with soft sandy beds between, and in these, besides the plants already named, Polypodium (?) occurs in fronds of large size and well preserved in the sandstone beds. For the next 150 ft. the beds overlying are soft and hard sandstones alternating, sands and sandy shales, and small nests of coal; and, beyond these, 50 ft. or 60 ft. of dark-green volcanic rock separate this lower part of the section from the higher beds, which are much the same in character” (1886, p. 102).
North Bank, Clarence River, opposite Tytler Stream.—Owing to a bend in the Clarence River the fault strikes across the river below Quail Flat and passes through a projection of the northern bank, on the end of which a small patch of Clarentian coal-measures is preserved. I did not cross the river to observe these, but McKay has given a section of them under the heading of “Clarence Crossing, Quail Flat” (McKay, 1886, p. 101).
McKay describes in general terms a similar outcrop three miles below Quail Flat, presumably also on the north bank of the river.
Red Hill.—According to McKay's description, the Quail Flat fault runs on the north-west side of Red Hill, which is composed of lower Clarentian rocks, while a narrow strip of pre-Notocene rocks occurs to their southeast side, along the banks of the Clarence River The lowest Clarentian rocks he describes as gritty sandstones and pebble-beds without distinct fossils. Next follow sandstones and grey, brown, or dark-coloured shales with plant-remains, not very well preserved, and thin coal-seams, 1 ft. to 18 in. in thickness. From a sandstone under the lowest coal-seam two fresh-water shells were collected. The succeeding beds are grey and soft yellow sandstones, with dark shales and plant-remains, including dicotyledonous leaves, a narrow leaf with parallel venation, and four or five species of fern. These are in turn followed by basaltic rock-tufas and sandstone conglomerates, alternating in an irregular manner, and finally by sandstones and pebble-beds, which in the north-eastern end of Red Hill are calcareous and contain concretions 1 ft. to 15 in. in diameter.
Clarence River below Bluff River.—There is a very considerable development of Notocene rocks from Bluff Hill across the Clarence River to Limestone Hill, which has not been satisfactorily explored either by McKay or myself. As seen from the north-east end of the valley Bluff Hill seems to form a syncline, and this impression is confirmed by the outcrop of lower Clarentian rocks on the north-west side of the Notocene outlier at the mouth of the Bluff River and north-west of Limestone Hill, where in a small creek I observed coal-measures—similar to those of the Herring River, overlaid by volcanic rocks. McKay (1886, p. 68) also states that the Buller series—i.e., the coal-measures—underlies the first great sheet
of volcanic rocks in Limestone Hill. Unfortunately, neither here nor in the Clarence River was the base of the series observed. If this great outcrop of Notocene rocks terminated to the north-west along a fault-line one would not expect Clarentian rocks except along its south-eastern boundary.
There must be a nearly complete section through this Notocene outcrop where it is crossed by the Clarence River, but as the river here flows in a gorge it cannot be closely followed. McKay describes the section as follows: “The lowest beds are sandstones and conglomerates, containing marine fossils…. These fossiliferous sandstones are overlaid by a considerable thickness of volcanic rocks, varying from 50 ft. to 200 ft., and these in turn by sandstones, conglomerates, and shales, followed by a second series of volcanic rocks overlaid by the limestones and grey marls closing the sequence.”
The fossils collected by McKay were determined by Woods as follows: Trigonia glyptica, “Modiola” kaikourensis, Thracia sp., and Belemnites superstes.
The base of the Clarentian is not here exposed, and it is quite possible that coal-measures are present. The lowest rocks I observed were grey sandstones about 26–30 ft. thick, with occasional pebble-beds, striking north, and dipping 25° to the east. These are followed by about 40 ft. of thin-bedded sandstones alternating with mudstones, and then about 300 ft. of massive sandstones with pebble - beds which are sometimes fossiliferous. The pebbles consist of quartzite, greywacke, grey gritty sandstones, jasperoid quartz, and occasionally quartz porphyry. The fossils collected included a belemnite, Trigonia glyptica, “Modiola” kaikourensis, Thracia sp., Aporrhais sp. and other gasteropods, and Dentalium sp. Evidently these are the beds from which McKay collected.
These beds are succeeded by a fine-grained basalt, here 50–60 ft. thick, with large amygdaloidal masses of calcite containing quartz crystals in druse cavities. This is separated from an upper lava or series of lavas by 30–40 ft. of sandstones. The upper lava is scoriaceous at the base, and porphyritic. Its thickness could not be exactly estimated, owing to faults and slips, but appeared to be upwards of 200 ft. It is followed by a bed of mudstone, about 20 ft. in thickness, full of volcanic material, and this again is followed by a third lava, fine-grained and more decomposed and at least 20 ft. thick. The dip of the beds at this point has flattened or appears to have flattened owing to the river flowing along the strike. The next-higher beds appear to be soft sandstones with ironstone concretions, dipping steeply. There appears to be a great thickness of these beds and further lavas before the limestone is reached, but the section was not followed.
On the opposite side of the Clarence River, in the Red Bluff, the section is similar except that the third band of lava was not observed. The top of the second lava is followed by upwards of 40 ft. of mudstones and thin-bedded sandstones.