Geology of the Provinces of Canterbury and Westland, New Zealand : a report comprising the results of official explorations
The Mount Torlesse Formation.
* Report on the Geology of the north-east portion of the South Island, from Cook's Straits to the Raiaia. By Captain F. W. Hutton, F.G.S., in Report of Geological Explorations during 1872-73. Geological Survey of New Zealand.
Thus to his Matai formation, which he now considers to be triassic, he assigns— although no fossils characteristic of that formation have ever been found in the whole Province of Canterbury or east of the Kaikouras—the western portion of the Malvern Hills, the Oxford Hills, and all the smaller ranges east of the sources of the Ashley river, notwithstanding that many of the rocks in those districts have sometimes a far more altered texture than those which compose the higher ranges lying to the west of the zone in question. And finally, the eastern portion of the Malvern Hills, the small ranges near Heathstock, and the isolated Black Hills, he places in his Pntataka formation, to which he now assigns a lower Jurassic age, relying principally on some impressions of ferns found in the Malvern Hills and in some other localities, which he considers identical with those obtained from some beds of Port Waikato, Auckland, and Waikava, Otago.
Now, considering the age of the Black Hills, where no fossils have ever been found, and judging from the lithological character of the rocks alone, they clearly belong to Captain Hutton's Kaikoura, or my Mount Torlesse formation, as they contain the same chertose altered beds as we find in the very heart of the Southern Alps. In fact, a series of rocks from that locality, and another from the River Cass (Upper Waimakariri) placed in the position of their sequence side by side, cannot be distinguished from each other, except by the labels attached to them. In regard also to the Malvern Hills, his whole arrangement cannot be accepted if we carefully study the sections in the district. These sections clearly show, first, that his so-called Putataka beds underlie his Matai beds, of which, amongst many other localities, a clear section is exhibited on the right bank of the Selwyn. On the northern or left bank of that river, the fern beds (his Putataka formation) are separated by an outlier of cretaceo-tertiary age (Hart's coal measures) from the higher ranges to the west, but crossing the river they can be followed on the southern side without any break till they disappear below that vast assemblage of rocks consisting of cherts, marbles, and diabasic ashes, alternating with large beds of sandstones, slates, and shales, overlying them conformably; consequently the fern beds cannot belong to Captain page 268Hutton's Putataka formation, as they are actually older than his so-called Matai formation, which he places to the west of it. The attached sections—No. 1 and 2 on section plate No. 2—offer all necessary details in illustration of this point.
Now, when we examine the relations of the beds which he assigns to his Maitai formation, with those of his Kaikoura formation, situated to the west of the former, including the whole of Mount Torlesse,. we observe that exactly the same sequence and character are met with in both; that, in fact, they both are portions of a series of folds in which a succession of chocolate-coloured slates and cherts form a good horizon for recognition. Thus, between Russell's Hills, (northern side of the Malvern Hills) and Mount Torlesse, a huge anticlinal occurs, the same rocks appearing on both sides, but dipping in opposite directions.—(See Section-plate No. 2, section No. 3.) Consequently, also, in this case, Captain Hutton's classification, based upon his observations made in a hasty visit to the district, does not hold good, and the whole series has to be included in the same formation, which I named the Mount Torlesse formation, from the large mountain system where I first studied it attentively. In several other localities I have been able to examine the relations of the different beds to each other in detail, always obtaining the same results. Amongst them, the most interesting one is situated in the Clent Hills, where I found, as far back as 1861, a series of beds, containing numerous impressions of ferns, and in the upper course of the Rangitata in Mount Potts, where I made a good collection of fossil shells. These collections were sent by me to Professor M'Coy in Melbourne for description, and I was informed by that gentleman that the former, the ferns, were of Jurassic, and the latter, mostly brachiopods, of upper Devonian or Lower Carboniferous age, both being identical with exuviae found in the New South Wales Coal-fields. Although at the time I believed this Clent Hill series somewhat younger in age than the Spirifera beds, I demurred at this definition, owing to the fact that the position and sequence of the strata and the character of the rocks of which both are composed, are alike. Since then it has been shown, and as I think with conclusive evidence, that both these fossiliferous strata—the Spirifera and Pecopteris beds—occurring together in the New South Wales coalfields, are of the same age and alternate with each other. The occurrence of Tæniopteris, which hitherto had been considered only of secondary age, seems to speak against a palæozoic origin; however, I page 269may point out that the same objection was made to the Glossopteris in Astralia, which has by overwhelming evidence been shown to be of palæozic age. I do not think that the fragment of a leaf, however distinct, can unsettle all that stratigraphical geology has proved to be correct. *
There is some difference in the character of these old sedimentary strata, going from east to west. It appears that whilst in the ranges near the plains we generally observe true littoral beds-the deposits of large rivers entering here the palæozoic sea-further to the west, as for instance, on the banks of the Upper Rangitata, we find their horizontal equivalents as rocks of a different character They consist of shales and shaly sandstones with marine shells, mostly brachiopods showing that they were deposited in deeper water than the Clent Hill beds, and some distance from the palæozoic coast-line.
In confirmation of my statements, I shall now proceed to give the usual sequence of the lowest sedimentary rocks as they appear in the Clent Hills district in an ascending order.—(See Section-plate, No. 2, section No. 4.)
The lowest beds are usually:
- 1. Slates greyish, sometimes very siliceous, alternating with sandstones, the latter gradually becoming of a coarser grain, so as first to assume the character of a grit, and afterwards of a pebble-bed.
Upon them repose:
- 2. Thick bedded conglomerates, in the Clent Hills several hundred feet thick In these conglomerates occur large sometimes fucoid-like carbonaceous markings, as if from drift trees. Smaller beds of sandstone are interstratified, partly ferruginous, partly ful of abscure remains of plants. Well-rolled boulders of greyish or greenish coarse sandstone, from the size of a child's head to that of a bean form the principal portion of the rocks, mixed sometimes with boulders or pebbles of chert and lydian stone Occasionally a few pieces of quartz, porphyry, and gneiss, which I found only after some search, connect the Clent Hill series with the beds of the Puddingstone Valley. In the latter, porphyry and gneiss occur in nearly equal
* The Rev. W.B. Clarke the veteran geologist of New South Wales, has given an excellent and exhaustive resumé on this quection in his various publications on the Sedimentary Formation of New South Wales, to which I wish to refer the reader.
- 3. Shales alternating with gritty sandstone, coal-sandstone and bands of clay-ironstone now follow. Some of the sandstones are full of the impressions of fossil ferns, others full of those of roots or of drift timber. Flattened stems of trees are also enclosed, often of considerable size, the bark altered to a scaly powdery coal (culm)* the interior filled with sandstone, often of a much finer grain than the surrounding rocks. Amongst the fossil flora I observed, Pecopteris (two or three species), Camptopteri?, Tæniopteris, Otopteris, Cyclopteris Sphenopteris, Cycadites? Palæozamia? Taxites.? Equisetites† The Pecopteris beds are usually distinct from the Tæniopteris beds Some of the shales consist almost entirely of the leaves and stems of ferns Amongst them the beds of sandstone are generally the most important some of them having a thickness of over twenty feet, although generally the arenaceous and carbonaceo-argillaceous strata alternate rapidly with each other, and are occasionally only a few inches thick; the whole thus having a ribboned appearance.
This series is together also several hundred feet thick.
- 4. No. 3 is covered by conglomerate beds like No 2 but of smaller dimensions.
* The following analysis of two specimens of this culm was made in the laboratory of the Geological Survey in Wellington:—
- 1, and 2, Bituminous Coals (Culm).
- Colour intensely black, lustrous, very fragile.
- Colour of powder black, that of ash light buff.
- No. 1 cakes freely, the other even more so.
Approximate Analysis. No. 1 No. 2. Water 2.27 2.12 Fixed carbon 55.10 50.04 Hydro-earbon 11.95 11.44 Ash 30.68 34.40 100 100
- Evaporative power of No. 1 =7.1
- Evaporative power of No. 2 = 6.5
† Dr. Hector has compared fossil plants found near Reefton, which also contain [unclear: Tæniopis], with the Rajamahal Flora of India.
- 5 The last series is overlaid by beds of shales and sandstones the latter having sometimes a semi-crystalline structure, and being of considerable thickness.
- 6. Upon them repose very thick beds of a fine-grained sandstone, which has the peculiarity that its matrix or cementing medium generally decomposes to a white powder. Many years ago, comparing this rock with similar rocks in Europe, I applied to it the name of Kaolin Sandstone with which it has a close resemblance, at least in outward appearance. Gradually this rock becomes more argillaceous, and is largely interstratified with shales.
- 7. The next horizon is formed of several beds of chocolate-coloured or brick-red slates. They are of various thicknesses, and alternate with greyish, greenish, or purple slates They are more or less arenaceous, of a very distinct character, and have been traced by me over a great deal of ground in several localities in this province as well as to the more northern portions of this island. From their lithological character and position, I believe them to be the horizontal equivalent of the cherts and diabasic beds which occupy the same horizon in the Malvern hills and elsewhere.
These beds are again overlaid by a series of beds consisting of clay slates often of yellowish or greyish tints, semi-crystalline sandstones, changing into graywacke, shales alternating with bluish gray and greenish sandstones, cherts, and many other varieties of sedimentary rocks too numerous to mention. Comparing these beds with those in Mount Potts—the only locality in this province where, as far as my researches have gone, the fossil brachiopods alluded to occur-we obtain the following results:—The beds 1, 2, 3 and 4 of the Clent Hills series are here represented by a great thickness of dark shales, often becoming so slaty that they may be termed clay slates, alternating with thinner layers of sandstone, sometimes with a ferruginous or calcareous matrix.
Amongst these deposits occur a few beds of conglomerate, which fairly may be termed bone beds, as in addition to boulders and pebbles of light coloured slates, they consist of great quantities of well rounded pieces of bones and broken shells. The bones are often of considerable dimensions. I was able to measure the proximal end of what was probably a humerus which I found to be eight inches across, and some other bones of similar dimensions; however, the bones, as before observed were so much rolled, and the cementing medium of such page 272considerable hardness that I was unable, with the tools at my command, to procure any characteristic specimens, but I have no doubt that they are of saurian origin. No teeth were visible amongst this bone breccia Some of the bones appearing to have been much rolled, resemble the vertebræ of Ganocephalous reptiles of the carboniferous period; as for instance, those of Dentrorpeton, Hylonomus, &c. I fail to see any resemblance between these vertebra and those of Ichtyosaurus, to which Dr. Hector has referred one of the vertebra collected by me, in his paper * "On the Fossil Reptiles of New Zealand," and upon the strength of which he concludes the beds in question are of Triassic age.
The whole of these strata form a large anticlinal in Fossil Gully and they are well and clearly exposed in this deep and rocky gome for several miles. They contain the following genera, and probably species:—Orthis spnigera, Spirifera (lineata, lata, oviformis duodecimocostata), Producta, Athyris, Euomplialus, Murclisonia Orthoceras, Encrinites, of which many resemble, or are closely allied to, Australian forms from the New South Wales coal-field series † They are covered by the same succession of beds as occur in the Clent Hills beginning with No. 5, and I may here observe that I was able to trace some of these upper beds, as, for instance, the chocolate-coloured slates, all the way from near the summit of the Mount Potts range to the foot of Mount Potts, five miles to the south.
* " On the Fossil Reptiles of New Zealand," by James Hector F.R.S. ''Transaction New Zealand Institute,'' Vol. VI, pages 334 and 336.
† I have not the least doubt that in future years, both the shell and plant beds will here be found interstratified with each other, as this has been the case in the coal-fields of New South Wales, and consequently that also in New Zealand, it will be clearly proved that they cannot belong to such distant periods as the carboniferous on the one hand, and the Jurassic on the other. Comparing them with well-defined European formations, they may, like the rhætic formation in the European Alps, be passage-beds, or represent the carbo-permian formation of the western portion of the United States (North America), where it has also been impossible to separate these two formations, which, in Europe, are so clearly and distinctly defined. When speaking further on of the Waipara formation, a similar difficulty will be placed before us, as here also the remains of mezozoic saurians and kainozoic shells are mixed with each other. Consequently, in this case, we have to deal with still another passage formation uniting two well-defined European divisions Thus had the geological nomenclature been based upon the strata of the Southern instead of the Northern Hemisphere, and the whole had been divided into periods, we should doubtless have included sanrians with the lower tertiary division, and the definition of palæozoic forms would have been much different from that Which has been obtained in European nomenclature. Stoliczka has shown also that the carbo-permian cannot be separated from the lower trias in the Himalayas, as these beds-are also closely connected by passage-beds.
As before observed, the more we advance towards the Canterbury plains, the more we are sure to find the conglomerates in exposed positions, having by their hardness, without doubt, resisted most effectually the disintegrating influences here at work for numberless ages. I have mentioned that the chocolate-coloured slates which overlie the fossiliferous beds forming the summit of the Mount Potts range, reach the Rangitata river-bed five miles more to the south. In order to show the huge dimensions of the foldings, I may state that these peculiarly coloured slates, with a series of more silicious beds, are again found on the opposite banks of the Rangitata, and are well developed in Butler's Creek, where it leaves the range's, and, still further to the south, they cross the Forest Creek near its sources. Between these localities and the summit of the Southern Alps, I have been able to trace them five times more (they may occur still oftener), always standing at a high angle, and showing well the clearly defined anticlinal and synclinal arrangement of the strata. Beds of conglomerate and shales are always associated with them forming a lower horizon, and also the texture of the sandstones is always of the same character, having either a white kaolin-like matrix, or being of blueish or greenish colours with a hard semi-crystalline structure. Moreover, these latter are always true graywacke sandstones, whatever their other characteristics may be, small angular pieces of slate being enclosed in them. These pieces are not always of the usual dark bluish tints, but sometimes exhibit reddish and greenish colours, proving that similar slates to those which now alternate with the graywacke sandstones were also existing before this large series of beds was formed.
Texture of Rocks and Position of Strata.
I shall now proceed to give a general outline of the beds of which this formation is composed, and of their general features and sequence.
Speaking more specially of their arrangement, we may describe it as a continuation of anticlinal arches and synclinal troughs; but instead of finding the mountains to be formed by the arches and the valleys by the troughs, careful examination shows convincingly that exactly the reverse has taken place. Thus to give only one instance, whilst the enormous mass of Mount Cook occupies a synclinal trough, the broad valley of the Godley river runs along an anticlinal arch. The occurrence of such enormous changes by which the arches or mountains have been converted into deep valleys, and the troughs into high serrated mountains, will give us a faint idea of the amount of time which has elapsed, and the enormous waste which has taken place, before the Southern Alps assumed their present form. The general strike of these sedimentary beds is south-west to north-east but varying considerably, sometimes even in short distances according to the numerous foldings and bends. The strata dip generally at high angles, and stand sometimes almost vertically, a south-east and northwest dip being the most usual. As the greater portion of the beds consist of sandstones of nearly the same character, we may describe the Southern Alps as sandstone chains. Alternating with the sandstones we find slates, shales, brecciated beds (graywacke), and conglomerates in almost endless succession, forming generally sharply defined strata. Here and there we observe inter-stratified with them diabasic beds, sometimes in the form of ashes. The sedimentary beds by contact with these ashes have undergone considerable changes, so as to assume all the characteristics of chertose rocks. Small beds of limestone, generally in the form of marble of whitish tints, are sometimes intimately associated with these eruptive rocks, whilst under all other conditions the absence of limestone is very striking, even rocks with a calcareous matrix being generally wanting.
Thus it is evident that we see before us the deposits of rivers falling into the palaeozoic sea, and judging from the position and succession of the boulders of which the conglomerate beds are composed, we may conclude that a large continent or island existed to the east or southeast of New Zealand, of which probably the old sedimentary and semi-metamorphic rocks of the Chatham Islands are still a small page 275remnant, whilst the main land has long since disappeared below the sea We perceive, moreover, that according to the state of the rivers or the changes of the currents, the character of the deposits also changed, the pebble and conglomerate beds representing the immediate neighbourhood of the months of the rivers, whilst the fine-grained Sandstones represent the littoral zone, and the clay-slates, and shales those regions of the bottom of the palæozoic sea where only fine particles of ooze could be deposited. The great scarcity of animal and vegetable remains in these rocks is very remarkable, and as we have no reason to believe that the sea was devoid of organic life, we either must assume that in many instances various agencies have been at work to destroy its record, or that from other physical causes animal life was very scarce. In order to explain more fully what I mean I may point out that there are markings or obscure exuviæ of an Annelid in many of the shales, which rocks consequently could have preserved to us those of Mollusks had they been abundant. I have found these identical fossils near the sources of the Rangitata and of the Rakaia, in the very heart of the Southern Alps, near the mouth of the Hurunui, on the East Coast, and in many localities in the Malvern Hills, whilst sandy shales with markings of fucoid plants, identical in character, are met with in many localities such as the Gorge of the Ashley, on the southern base of Mount Cook, and in the Tour Peak range.
If we apply the late deep sea researches and their inductions concerning the Mediterranean, as given by Dr. Carpenter, F.R.S., and Mr J Gwyn Jeffreys, F.R.S., in the Proceedings of the Royal Society, Volume XIX No. 125, to the physical conditions which might have prevailed in our palæozoic seas during the formation of the New Zealand strata under review, our difficulties under that head will be easily removed We know that in our palseozoic strata there are beds of conglomerate of enormous thickness, the boulders of which they are composed showing that they must have been derived from ranges of great lithological variety, and indicating that they were brought down by large rivers, whilst the general character of the whole strata associated with these conglomerates indicates clearly that they could only have been formed from the sediment of such rivers. Thus it is easily conceivable that one of the conditions might have existed which now prevails in the more central portion of the Mediterranean to the prejudice of the existence of animal life, namely, turbidity of the bttom water. Of course this might have been only one of the causes page 276of this remarkable scarcity of animal life, but I need scarcely point out of what value it is to the geologist now to be able to account for facts which, before the deep sea dredgings lately undertaken, could only hypothetically be explained. However, in one locality, there is ample evidence that animal life was not missing, by the occurrence of fossiliferous beds on the western side of Mount Potts, Upper Rangitata, for it contains many brachiopods and a few gasteropods, of which I have already given the principal genera on page 272.
The lowest beds visible consist of shales often very carbonaceous; of micaceous gritty, generally tabular, sandstones, mostly of light colours, some of them being full of fucoidal markings. The shales are often slaty, and have a peculiar serpentinous look; probably they consist of ashes or are altered beds. Associated with them are conglomerates, the matrix of which, mostly a quartzose ferruginous sand, is sometimes so little binding that it is easily decomposed when exposed to atmospheric action, but some of them are so hard that they form buttresses standing prominently out from the mountain sides, and then generally form the summits of the ranges. These conglomerates, like the succeeding beds, are often grouped in several horizons separated from each other by thousands of feet. They are overlaid by a series of compact diabases, diabasic tufas and cherts, with occasionally beds of more or less altered limestones between them. Where these latter occur, they very often constitute the summits of the ranges; thus, to give only one instance, they form in the Malvern Hills, the summits of the Flagpole Hill on the one side, and the Four Peak range on the other; while between them the saddle is an anticlinal, consisting of loosely cemented conglomerates of the lower beds. As before observed, the diabases of the Malvern Hills have a compact structure, and I may here add that the more granular varieties of the same rock occurring in the Nelson province, have without doubt been erupted in the same geological period, and are of a similar origin.
It is very striking that these rocks have such a large extension in our palæozoic beds, both vertical and horizontal, and that in this respect they closely resemble the diabases of the Hartz Mountains in Germany, where they are also interstratified in beds of considerable thickness, ranging from the lower devonian to the upper carboniferous period. Professor E. Kayser, of Berlin, has given an excellent monograph of these Hartz beds, in the Journal of the German Geological page 277Society for 1869, which is so applicable to our own Malvern Hill beds, that in most instances, if we would substitute for the Grerman names such as Alrode, Lupbode, &c., our New Zealand names Selwyn, flagpole Hill, they would describe and figure perfectly well our own sections. This shows once more convincingly, that however far the distance may be which separate two localities on the globe, the same abysso-dynamic causes were at work to build up the solid crust of the earth, tinder the same conditions, everywhere in like manner. Like the conglomerates, these diabasic beds occur in many localities all over this Province, but they are generally not so conspicuous as the chertose rocks, altered by contact with them, which often form turreted crests on the summit of the hills, or run up like walls on the mountain sides.
They are succeeded by sandstones, shales, and slates of various characters, of which a peculiar fine-grained sandstone, with a white decomposing matrix, is sometimes largely developed. In some localities, the latter is interbedded between the conglomerates and the chocolate-coloured slates or their equivalents, the diabasic ashes. The whole series is always of great thickness, folded in a remarkable manner, so that the beds stand at a very high angle, and sometimes even vertical. In some districts, rocks of the same facies forming beds of great thickness prevail. In others, beds of an arenaceous nature preponderate; whilst less frequently, shales or argillaceous beds of a slaty texture take their place. However, in many instances, the beds are very thin, and alternate with each other in a most remarkable manner., the divisions being sharply defined. I shall here give only one illustration to show this. On the left bank of the Grodley river, near the glacier of the same name, where a high cliff rises from the water's edge, the ribboned appearance of the beds was so conspicuous that I measured a small portion of the section consisting of greyish sandstones and dark bluish clay-slates, the latter in a few instances gradually getting thinner in their higher portion, and disappearing altogether, a bed of sandstone taking their place. The whole beds dip at an angle of 46 degrees to the south-south-west, and, follow each other in ascending order:—
- 8 feet 0 inches, greyish fine-grained sandstone
- 8 feet 3 inches dark clay-slate
- 8 feet 4 inches greyish sandstone
- 8 feet 3 inches dark clay-slatepage 278
- 8 feet 2 inches greenish sandstone
- 8 feet 3 inches dark clay-slate, running out 12 feet above river
- 8 feet 4 inches greyish sandstone
- 8 feet 2 inches dark clay-slate
- 8 feet 3 inches greyish sandstone
- 8 feet 4 inches dark clay-slate
- 1 feet 10 inches greenish sandstone
- 1 feet 0 inches dark clay-slate
- 3 feet 0 inches greyish sandstone
- 3 feet 4 inches dark clay-slate running gradually out
- 6 feet 2 inches greyish sandstone
- 6 feet 9 inches dark clay-slate
- 4 feet 3 inches greyish sandstone
- 4 feet 4 inches dark clay-slate
Above the latter bed, repose bluish greywacke sandstones full of small quartz veins, about 470 feet thick, after which another alternation of sandstones and slates, similar to the one given above, follows, succeeded by a series of shales of great thickness, overlaid again by bluish graywacke sandstone.
This formation, as before observed, covers more than half of the Province of Canterbury; near the Hurunui, as well as at the Waimate, some of its outliers reach almost to the sea coast and from the northern boundary, it stretches to several miles west of the junction of the Otira with the Taramakau. From the Hurunui it recedes in a south-west direction inland, and forms all the higher ranges skirting the Canterbury plains and their southern continuation as far as the Waitaki. Rocks belonging to this series form, from the banks of the Taramakau for a considerable distance, the summits, and for several thousand feet the western slopes, of the Southern Alps, till we reach the northern sources of the Rakaia, where they retreat several miles to the east of the main divide. More to the south they again build up several of the highest peaks of the Southern Alps, as, for instance, Mount Haidinger and Mount Cook, of which we obtain clear evidence from the moraines covering the glaciers descending on both sides. From the gigantic ancient moraines along the West Coast, we can collect, in most localities, numbers of blocks derived on this formation, which is an indication of its presence in many in-page 279accessible peaks. South of Mount Cook, the Mount Torlesse rocks strike more towards the interior, the boundary between them and the Waihao formation passing near the sources of the Ahuriri river to the neighbourhood of the Lindis Pass. They are here separated from the large outlier occurring on both banks of the Hunter river by a small zone of the Waihao formation, which crowns the ranges east of the Hunter river. Another outlier is situated not far from the West Coast, south of Jackson's Bay.
Thickness and Age.
Before concluding the somewhat imperfect sketch of this extensive formation, which has at least a thickness of 25,000 feet, and besides the fossils enumerated, contains only two other small and rather indistinct exuviæ, of which one resembles a tentaculite and a few tracks of anellides, I wish to point out that it is far from my thoughts to say that the whole of this formation is of carboniferous age. It is very possible, and even more than probable, that this huge assemblage of beds, by which it is formed may belong to several distinct periods, ranging from palæozoic to lower mezozoic; but owing to the want of fossils, such as have been found at Reefton (of devonian age), at Richmond in the Province of Nelson, and in the Moonlight range and other localities in Otago (of triassic age), or again in the south-eastern district of Otago (Captain Hutton's Putataka formation), it is impossible to divide this formation in Canterbury for the present at at least, into smaller groups, the more so as such attempts have hitherto only brought confusion into our geology. Nothing remains to be done but to make further detail examinations on a systematic plan, and to follow some of the more characteristic beds as far as they can be traced.
I have already alluded to the diabasic beds and their ashes, which are interstratified in many horizons between the strata of purely sedimentary origin; besides them, are a few dykes of hyperite, which might have been injected when the huge foldings were formed. In one instance, in Coal Creek, Rangitata, I found a bed of melaphyre, somewhat amygdaloidal, interbedded between two strata of sandstone, but it had probably been forced between them at a much later date, belonging to the formation next to be considered.
Relations to the Older Formations.
There is no doubt that great unconformity exists between this and the Waihao formation, of which clear proofs are to be found near Burke's Pass and the Waihao country. In the Southern Alps proper, the boundaries between the two formations are not so clearly defined, in most instances no break being visible. In such cases, it is impossible to define the boundary line between them, the facies of the rocks being the only guide. Amongst the localities where this unconformity is to be observed, one occurs near the head of the Stewart, one of the source branches of the Rakaia, another twelve miles up the River Hopkins, and again on the slopes of Mount Brewster, but generally in ascending the rivers, we cross from one formation into the other, without observing any difference in the strike and dip of the strata.