Geological Notes.

Timaru Herald, Volume XIIC, Issue 13520, 15 February 1908, Page 2 (Supplement)

Geological Notes.

son ii i-.\\TKi:isi'i:v. ,ISy J. llaldcastle.} The folhiwini; n-tes i.n ihe tboh.gy nf Nrith Canterbury are Hi'.- result mainly „f ]>; .| 1 observations made in odd 'lays nf lei.-urc during a quarter of a century. :.iil.'<l hv mueli nailing of geological writii,.r>-. v ."iv lilt 1..- of which, however, had r. Terence" in -South Canterbury. Ihe subject hab been tleali' with as *imply as pcsMble. The method of treatment is unusual. Geological writeii-.. as a rule. divide the subject according to changes j" the life forms preserved as fossils. In tlr-.-c nnls changes of elimate and "I land and sea. have been adopted a.-, Hilines of demarcation, hence no knowledge of fossils i, required to enable the reader to follow the .-lorv as here worked out. I.VI jIODI'CIORV. 'Hi- geology of Canterbury fn 1 :■-* naturally., at "all events easily, into two oivi.-.ior.s. Ihe Great Stotic Jiook, as the geological ivcord has well been called. i.> presented foi our observation and study in hid di-lincl volumes, an earlier and a later. The earlier volume consists of what Dr. Hell has well named "The Old Land," the various kinds of hard and dense, slate and i-aiulstone rocks composing cur mountain ranges : the Southern Alps and their great tours; the frontal range.;, with their outstanding height*-, Mount Four Peaks, Mount Peel. Mount- Misery and the Mothers; the long ridges of the Hunters Hills; and, the mass of hillv country between ihe Hunters Hilli, and tlie Waitaki. Ihe same kinds of rocks doubtless underlie all our low country at dentin: of a few hundreds or iliou.-ands of feel beneath '-he present surface. One of them was ■struck at'; a depth of about 400ft-. in a bore well at the Atlas Mill in Tiinuru, and put an end to the boring. This older volume has been so much knocked about, its folios disarranged, crumpled, and crushed, ;uid the original character obliterated, to such an extent thai the volume ii very difHcult to read. In the following papers this volume will be passed over, and attention confined to the later one, lbs history of the lowland region, which is comparatively easy to read. THE"MOUNTAIX ROCKS. A fe-.v general remarks about the mountain recks may, however, be useful. The whole of our mountain ranges are formed of material* that were once loose and incoherent- sand and mud, shifted about by riven; and seas —chiefly by rivers and smaller si reams. The rocks were therefore originally laid down Hat, as sea-beds, lake-beds, and river plains, -.uul probably when in -that condition wore at no great elevation above >ea-level. The soft water-laid deposits were afterwards consolidated by loading and by lateral pro sureti. were cemented by infiltrations and chemical processes, and subsequently, by the enormous forces- that are operative u'illiiu the earth's crust, were squeezed and folded, and crushed and broken, and uplifted into ridges that in the Alps rose many thousands of feet above sea-level and above the surrounding land. In many places strata that were laid down Hal have been broken and tilled '.-o I hit llu-y are now standing on edge. The Alps- and other ranges are only remnants of the original folds, after frost and thaw, flowing water and Mowing ice, and other destructive agencies have- acted upon them for an immeasurable, period o! time.. It is quite likely that as much material has been removed—wor.-i away —from our mountains as they now contain, for in many cases the tojis of ridges of the present day were the bottoms of the original folds. It is bewildering to try to grasp the fact, bub a- fact it is. that the whole of the materials' of the earths crust accessible to observation in •South Canterbury have been shifted again since the earth was formed. .Some of the materials may have travelled long distances; s-ome of the rocks have certainly been made and r/.made many lim<» over." And to-day the Alps and lcw:er -iniiieneis are being slowly worn down and drifted away on fresh journeys, to be formed into new rocks once more. Whence came all the sand and mud that went to make up our mountain rocks originally, still remains to be discovered. Sir Julius Von Haast believed that some of it at all events came from a' land now submerged beneath the sea to the eastward, unlets, indeed, the Chatham Islands are a remnant of it. The formation of the mountain rocks and the squeezing of them into mountains, occupied an enormous length of time. Neither the deposition of the materials nor the elevation of the ridges would bo a continuous process. Elevation, especially, would go on by litis and starts, with lons intervale between periods of great activity. Von Haast divided the mountain rocks of Cant-e'ibury into two series. To an earlier series he' attributed some very much altered sedimentary, (i.e., waterlaid) rocks, chiefly found on the western side <-f ihe Alps, but including some portions of the eastern country, viz.. the block of hilly country on the ea.-tern side of the Hak'ataramea Valley, tin; range I mining thence to Rurke's Pay*, some parts of the- Dobson range beyond the Pass. The IJrothcr.s and Mount Misery, and the Kakahu and Waitohi Hills in part. The rest of the- mountains are composed of less—-but still greatly—altered sedimentary rocks. Most of them arc fine-grained sandstones and slates. In North Canterbury, however, Haast describes thick beds of conglomerates, or hard cemented gravels. The oldest rocks appear to have been formed at a time when there was little or no life on the earth that could leave any record of its existence in the sha|se of fossils, whfile some- of the newer rocks contain many relies of highly developed forms of life. There are, however, few fossiliferous- rocks in our South Canterbury ranges, and very little indication that the mountain region was ever submerged beneath the sea. One example of a calcareous rock suggestive of marine origin is- a patch of marble at Kakahu. an altered limestone mixed with what Von Haast took to be volcanic ashes. A slab of t.his blue and white stone was shown in the South Canterbury Bay at ill" C'mi-tchurcli Exhibition. Further north In- found many marine fossils in ill- mountains, as well as vestiges of vegetable life. 1 have met with fossils in " Old Land" rocks in pebbles in the Waihi (Jorge, these being black and glossy prints of vegetable matter in a. line-grained muilstoiie nearly as black as the- prints: and in the bed of a creek flowing into the Waihi I saw very tine prints of fern fronds, in a similar rock that is now standing on edge. These are ihe only traces of life I have met v.iih in mountain rocks. The very latest rocks that were formed before the close of the iiK-uiitain building period in this district had not time, or were not placed under suitable conditions, to bi-'-umc- hard rocks lie-fore, thev were uplilt ■■■!. 'lhese oft rocks hiiv'e been aim ■-.-». entirely destroyed and removed i'l Milis-qtieut ' ages. h might be expected, however, that some fiairuionts of lliem would remain, in situations where they would b.- protected from denuding agents, and this seems lo have been the ca>v. fur in of our riverbeds one may find « • |»obbles of comparativoly M.fr .sandstone, which have come rrom lock smiiewli •>■- In the hills. On lb- we-» coast of this island, and b.-st known in ihe Rulh-r Valley, there is a formation of i-oan-v conglomerate. mm liniii'i .-earns of bituminous coal. The f;i auriferous cements of the Blue Spill- .-Mid r-1.-11-.-d locks 111 Otiljro :il- pi ob

ably ( ,f the same age, and these appear, froin their pm-itious. lo belong lo the liiouulaiu rather than lo ihe lowland seli-.:-. That is to .sav. lliw appear lo have been formed before ill.- close of thegreat mountain uplifts. 'lhe climatic conditions lhal produced material for coarse conglomerates in the Buller Valley and in Olago. must have produced such material in South Canterbury also, and if the conglomerates are really absent here, the fact must be attributed lo the activity of denuding agents in later times, and to the comparative eas_- with which soft young rocks could be destroyed, after being disturbed bv elevation.

It is important to note thai until we reach those conglomerates, among the latest of the mountain rocks, the geological record contains no entry of the action of frost. Conglomerate's of course shingle, and all other extensive depu-its of coarse shingle, do imply the action of fnst, in quarrying and breaking up the rocks for ihe rivers or sea-coast bleakels lo roll into rounded pebbles. Our mountain rocks therefore span the long period of geological time fri.m the earliest lifeless age to one in which life had become w.-ll established, and I hey al.-o span ih. period commencing with Ihe perennially' hot climate of a hot. earth and closing with a climate which, iu winter and on the mountains, at all events, was cold en.nigh to cause frowls that shattered exposed rock surfaces. The more intense processes of mountain elevation appear to have come to an end in South Canterbury with the effort which included the ridging up of the soft sandstones land the conglomerates- just referred lo), though there were in later times- some important uplifts among the mountains of North Canterbury and further north, and also in Olago. There were some minor uplifts and important changes of level in South Canterbury, as we shall see later on, but the formation of high and narrow folds of rock, out of which mountains i-Mild be carved, was not again repeated. There api»eai-.s lo have been little or no volcanic action within South Canterbury during the mountain building period, except on the northern side, between the Orari and the Rangitata. A good many boulders- and pebbles of volcanic rocks may be found in the beds of those rivers. Further north, Mount Somers. the Port Hills and Ranks Peninsula, are volcanic mountains, the former certainly belonging to the mountain-building ages, the latter probably, though it may be younger. It would take 100 much space to discuss theories- of mountain building. It must suffice to mention that no theory yet put forth is accepted by geologists as completely satisfactory. The most popular theory—that the crust is being crushed through the earth as a whole contracting because it is; cooling—is said to be merely " worthy of provisional acceptance as the most plausible explanation as yet available." Theories of mountain building require some sort of assumption to bs made regarding the condition of the earth's interior, and quite recently, the difficulty of framing a satisfactory theory with tin.-, aid of the current assumption of contraction through cooling, ban' led liw-o prominent American geologists to .suggest a new hypothesis as; lo (he condition of the interior of the earth, viz., that it- is an aggregation of solids promiscuously put together, and lhal if has not yet settled into complete compactness and solidity—much as a railway embankment of rough lumps of clay would require sonle -time lo become consolidated. Tht- pr-Mxss' of consolidation of a huge planet constituted in that manner would necessarily go on by fits and starts, and be apt lo produce some striking effects at the surface. So far nothing has been said of the condition of lowland South Canterbury during the long mountain building period. The fine-grained hard rockis doubtless underlie the whole region. Then, during the lateist phrase, or perhaps after the close of the mountain-building age, there is some evidence that the lowlands were submerged beneath the sea. Near , 10, and probably next Lo, the slaty rocks on theh Lower Pareora gorge, in the riverbed below the Tiniaru Waterworks clam, there is a patch of hard, shelly sandstone, evidently a fragment of a shallow- marine formation, probably laid down between tide levels. It is well stratified, and contains layers of broken shells—broken by dashing on the rock of Mount Misery of that- day—and it includes some good sized pebblus of a ceurse sandstone. An ammonite has been obtained at Kakahu, and ammonites are fossils of an earlier age than that of our lowland formations generally. Further north, in the Waipara country, there are other marine fossils of an older type than exist in the marine beds of this district, omitting the ammonite bed of Kakahu and possibly the patch referred to in the Pareora. and these may all belong to an age of submergence of the lowlands after the mountains- were uplifted. Assuming this to be the case, the degree of submergence indicated falls short of that which we shall have lo deal with presently. Convenient hand specimens of some of the mountain rocks can be collected in any riverbed or \>u the sea beach, but not by any means a complete series, as only the hardest pebbles survive the- wear and tear of a journey down a, river, and the drifting movement- along the sea beach is still more destructive.

The majority of the pebbles on the sea beach and riverbeds are bluish-grey in colour, and ?»i the great majority of eases it is: easily i:een that the original constituent's were fine sand or finer mud. The mud stones are now hard and slaty, the sandstones are dense and more or le-'s crystalline. In many casts the lines of original stratification are more or le.-s plainly seen, and some of the pebbles are ihe more interesting in this respect, as containing both coarse and fine layers. Many of the crystalline sandstones contain numerous small chips of a black slate, not at all waterworn, suggesting therefore a source for these quite near to where ihe sandstone was laid down. Portions of the rock in the Waimate gorge are thickly packed with these chips. There are ln-iuy other kinds of pebbles, in small numbers, notably white ones of quartz, and a smaller number of red, yellow, green, and vari-coloured ones. All these, and the quartz pebbles. ;l re probably derived from veins deposited iu the mountain rocks since these- were consolidalcd.

A good many of the grey pebbles contain thin while veins, which often project i-Jighty because they aid harder than the rest of the stone and have resisted wear better. The rocks in the hills contain much larger veins, -.some of them wide enough to be called reefs, and the breaking up of these .supplies quartz pebbles. The white streak on the outside of a pebble, is. of course, the '. dge of a plate of quartz running through the pebble. An interesting point about thesxe white plattis and the lines that represent them on the outside, is that in many pebbles they run in two directions, one crossing the* other. In ~-in-. eases it can be r-:en that one set of lines has been broken through and the broken ends displaced: The occurrence of the white veins implies that the grey rock was shattered, and that the cracks and fissures produced by the shattering were afterwards filled up by a deposit of quart/, that cemented the whole into solidity again. In the cases- where rwo set-' of planes inleii-ect each other, and one of them ha.s been displaced, we see in ihis 'combination lhal the rock was shattered and cemented a, second time, and that not only was it. shattered but that the fragments were moved amongst each other, and thivs were produced ii)iniafur-» 'fault-" Doubtless .similar movement-

look place in the ea,-e of the first shattcriij" uttt in I lie absence of marks such ao°the lir.-t. white vutb .supply tor the second, the movement canii.L hi- detected. Some of these miniature laulimgs took place under such circiif.if.-tuiu.vs thai no open hV.ure was lett lo be hlled up, but a displacement of the tins I '<-'t of veins and ii dark line shows where the second fracture ran. In larger boulders in the riverbeds larger veil/- and larger faults mav be found, these being gradations Lo-w-aids the wider reefs, and the- faults measuring thousands of feet in the mountain masisus. In the mountains themselves portions of the strata may be found that have been crumpled as one might squeeze together a skein of wool. The . hardest . boulders on tho Ninety Mile beach are whitish, cream-coloured, or sometimes blackish stones, composed of quartz sand, occasionally of quartz gravel, presenting a sugary appearance when broken. These do not. belong to the mountain scries proper, but to a later ,a"c. and their origin will be described wdien we come to treat of that age. It is necciisary to be cautious, in collecting specimen pebbles from the liverbeds of to-day, against assuming as a certainty that the pebbles in any river came, from' the mountains now drained by that ■ stream. This coin ion applies particularly lo the Tcmuka. Waihi. and Orari, which flow through ancient gravels laid down by thi- Rangitata, but it may apply also in some other cases under like circumstances. The difference in materials, texture, and hardness between the mountain rocks and the later ones, is iso great as to indicate- a great gap in the record, which may possibly be filled up, to sum;; extent at all events, by formations ,found elsewhere in New Zealand. THK LOWLAND FORMATIONS.

The second volume of the Great Stone Book contains the record of the geological changes which South Canterbury has undergone since the mountains were upheaved, and these • changes have been strange enough to make the perusal of the record extremely interesting.

The most important question that can be asked concerning the physical geography of any part of lire earth's surtace is: Is it land or water? Or still more importantly, with a seemingly .small variation : lis it land or sea' And the question next in importance is: What is the nature of its climate'' On the conditions implied in the answers to these two questions depend the character of the physical changes t lint take place on the surface, and the character of the living forms, animal and vegetable, that occupy it. The same questions are of equal imi>ortanee in geology, and by applying them to the geology of South Canterbury —the application is easy—the record isdivided into clearly defined chapteis. The division must be made, in order to avoid confusion and perplexity. Each division represents a long period of time, and is distinguishable from those preceding and following it by distinct changes in tlw nature of the rocks we have to study, these indicating a change from dry iand to sea or vice versa, or a distinct change of climate. THK COAL AGE. A careful study of the district within, the range of my opportunities, and a careful perusal of all that 1 have met vith in print, on the isubject. leads to the conclusion that, notwithstanding the evidence mentioned, of a submergence following, the mountain building period, we must start the geologic history of the lowlands- with the fact that- these were dry land, of unknown extent eastwards, and bounded and interrupted on the west by mountains almost precisely as at p'csent.' In regard to the eastern extension of the lowland, it may be noted here, thai a comparison of the flora and fauna!' of New Zealand and South America, has led to the conclusion that at the time we are now dealing with, or at some later period, these lands were connected as parts of an Antarctic Continent, and that was 'perhaps more likely to have been the -.case in this earlier time than in any later one.

AVhether the land between, the mountains and the sea, or say, as far east as the present coast-line was a, level area, we cannot tell. We' have, no indication of the nature, situation or direction, of any inequalities that may have roughened its* surface, and we must therefore be content lo think of it loosely. as an expanse of flat country. The first fact that we have to bear in mind is that we have to deal with an area -of dry land; not without fresh waters, of course, iu livens and smaller si reams, and not without hollows occupied by lakes, as we shall see. The next important general condition is climate, and we shall find abundant proofs that notwithstanding the fact- that friTils appear to have been at work liefore or soon after the close of the mountain building period, the climate of this legion at the time we are now to deal with, was" either tropical or sub-tropical. At all events it was absolutely frostles-s.-Climate, of course, is nowhere a merely local .phenomenon, and if South Canterbury possessed at this time a hot climate, this' condition must have been common to the whole of the area now occupied by New Zealand, and there is abundant evidence that- it was so. > The deposits forming the first section of the record are of considerable importance from an economical point of view, but thev .occupy only a small space in our landscapes. They are limited, so far as they are accessible in this district, to a comparatively thin series of beds that, have been for the most part buried under later formations. Based upon the mountain rocks, abutting on the flanks of the mountains, here and there stretching a few miles from them, and often exposed in section where streams on leaving their gorges in the slates have cut down their channels in the softer rock, we have beds of finegrained and usually white or pale-coloured clavs; beds of sand of all degrees of fineness and coarseness, usually white, unlets stained with coaly matter or -oxide of iron ; white grits "and gravels of quartz ;' and in some localities we have seams of. brown coal or lignite, eome of which are economically useful. The clays are in many places* quite white, and for that reason are commonly called pipe-clays. Such are the clays of Kakahu, which have been proved suitable for making rough domestic pottery and a similar clay at Sutherhinds. used at Tiniaru for making glazed sanitarv pipes. These clays and sands are found in larger or .-mallei' quantitiis at many points throughout the district, along the foot of the ranges. South Canterbury—the whole of this Island, in fact—presented at this period an aspect absolutely different from that of ihe present day. "and comparable only with some verdant area within the tropics. Favoured by an abundant rainfall and a high temperature, the whole region was covered with a luxuriant vegetation. Excepting perhaps the tops of the highest of them, even the mountains were probably towering masses of greenery, and the' low country bore broad expanses of swainpv forests and jungly reeds, and drier ground doubtless bore a luxuriant nrowth of grasses. Trees allied tr. the kauri and araiiearia grew here, and ferns are common fossils of the age. There can be no doubt- about the wealth of vegetation, for this was the coal age .of South Canterbury and of New Zealand. There were, it appears, some seams of eoal formed at an earlier age on file WestCoast, but the bulk of the Wast- Coast, r.0.-ds, and all these found on this side of the mountains-, and probably also all those of the North Island, were formed in (lie •-amc geological age as ours. There, is sonip indication in the character of the. ,T.-M'cialed marine fossils, that the coals , ; f Xe«" South Wales are als-p of the sa-uie

a"c. llu: superiority "£ L Vr*'' coal.s to "in- eastern In-own coals and lignites is not due to difference in age, hut to their having been subjected to different treatment by nature smc the materials for tlK'in were put together. (To be Continued.)