Art. XLIX.—On the Disposition of Alluvial Deposits on the Otago Gold Fields.
[Read before the Otago Institute, April 12, 1870.]
The remarks 1 am about to make I crave indulgence for, as I can lay no claim to scientific attainments, and my experience of the appearance and physical construction of the country has only been gathered during some four hurried business journeys of about ten days each, being in fact little more than could be gathered by an ordinary coach traveller from Dunedin to Queenstown and Skippers, a distance of about 200 miles.
The question I am about to discuss, embraces the terrace formation of our inland plains or basins, such as are observable in those of the Maniototo, Dunstan, Cromwell, and Queenstown; also, the question of deposits of gold in old river beds, which we commonly term deep leads. The first of these basins—the Maniototo—is reached by proceeding up the Shag Valley, over a saddle in the spurs of the Kakaunui mountains, via, Pigroot. I do not allude to the terrace formations in the Shag Valley, except to state my belief that they have the same nature as the rest. The line of elevation also at which the coaches travel up this valley is not favourable for noting these features. In descending the saddle from Pigroot into the Maniototo Plains, our view embraces the Rock and Pillar Range, lying slightly to the left; the Kakaunuis, over which we pass, extend to the right, till they reach the Mount Ida Range, succeeded by the Little Ida, Hawkdun, St. Bathans, and Dunstan Ranges, which are at about right angles, and extend along our route up country, and form an arch or bow-like right hand boundary as far as the Dunstan township. From the Rock and Pillar, on the left, at some distance a-head, the Rough Ridge shoots out across our path, and may be said to join the right hand ranges at the Little Ida, and thus form the Maniototo Plains. Passing over the Rough Ridge, at a low elevation, our road crosses the Ida Valley, the extreme left of which is under the Pinelheugh Range, Raggedy and Blackstone Hill Ranges, crossing our road from the left in the same manner as the Rough Ridge, and joining the right hand range at about the junction of the Hawk-dun and St. Bathans Ranges.
Passing out through Blackstone Hill we enter the Manuherikia Valley, the left hand boundary being the Blackstone Hill and Raggedy Ranges as far as the township of Manuherikia. At this point we meet the Molyneux River, which here flows across the valley for about seven miles from the Dunstan township, where it enters through a gorge, about thirteen miles long, which it traverses from the Cromwell Basin. The Manuherikia Valley (across the river) is bounded by the Carrick and Old Man Ranges, and a few spurs of no considerable elevation, in which are Conroy's and Butcher's Gullies.
The drainage of the Maniototo Plains is effected by the Taieri River, which takes its rise in the Lammerlaw Range, entering the plains between the Rough Ridge and the Rock and Pillar, which it skirts, and finds an outlet under the same range, at another point between that and the spurs of the Kakaunuis, to the left of the saddle over which we are presumed to have journeyed. This river is fed by the Swine and other burns flowing from the ranges on the right hand, and by the Kyeburn—which takes its rise at the mount of that name, in the neighbourhood of the Maruwhenua Pass, flowing along the foot of the Kakaunui—and joining the Taieri River in the neighbourhood of the Taieri Lake. The land under Mount Ida, and at the township of that name, would thus appear the highest in that district, and higher than the Ida and Manuherikia Valleys. The Ida Valley is drained by the Ida Burn, which takes its rise on the right hand, and the Pool Burn on the left; these two join together at a gorge in the Raggedy Range, and flow through it in one stream into the Manuherikia Valley and river of that name, which at the township of the same name, joins the Molyneux River, and then passes through a gorge down through the Teviot Basin. The Ida Valley is also drained on the extreme left hand by the Manor Burn, which takes its rise between Pinelheugh Range and Rough Ridge, and also joins the River Manu- herikia. The Ida Valley is thus higher than the Manuherikia Valley. The Manuherikia Valley is drained by the river of that name, and by the Lauder, Chatto, and Dunstan Creek tributaries.
In the Maniototo Basin, on the Rock and Pillar Range, there are alluvial diggings at Hyde, extending to no very great height above the water level, and at Hamilton, at an elevation of about 800 feet or higher, and Mount Ida, under the highest peak of the range of that name. Latterly, also, at the Kyeburn River, at about the junction of Mount Kakaunui and Mount Ida Ranges, in the vicinity of Mount Burster, not far from the Maruwhenua Gorge.
In the Ida Valley, the diggings are at the Welshman's and German Hill, one of these being in either face of Blackstone Hill and the Rough Ridge, at about the centre of the valley, and both at some elevation, say, at about 100 feet above the water level. I am informed there have also been some deep alluvial workings, to about 150 feet, under the Raggedy Ranges, at Black's No. 3, the lead running parallel with the ranges, and under a terrace formation. In the Manuherikia Valley, the diggings are at St. Bathans, Drybread, Black's No. 1, Manuherikia, Conroy's, Butcher's, the Fraser River, and Mutton Town Creek; the banks of the Manuherikia and Molyneux. The beaches or exposed portions of the bed of the latter river, during hard frosty weather, have been also extensively worked, with extremely rich results, especially where perseverance has been shown by the miners working below the water level, as at French- man's Point, at the junction of the Manuherikia and Molyneux Rivers. Extremely rich returns have been secured by the dredgers on the Molyneux
River, from the Hospital and Hartley and Riley's bars or beaches; these two places, in fact, may be likened to two ripples placed by nature in her sluice box, the Molyneux River, and there are, without doubt, many equally rich places. At the Dunstan township, the road enters the gorge, and continues by the river side to Cromwell; at the former place the banks are about 35 feet high, and at the latter 75 feet. The gorge is filled with immense water and ice-worn rocks and boulders, and at places on either bank a terrace formation is observable.
Our road to the Wakatipu, or Queenstown Basin, lies up the Kawarau River, which, at Cromwell, joins the River Molyneux in its course from the Wanaka Lake. After crossing the plain, and temporarily losing sight of the river, we again fall in with it on entering the Kawarau Gorge, through which we pass in company with it till we reach the Arrow District, at the lower end of the Queenstown Basin. The Arrow River, which takes its rise under Mount Hyde, flows into the Queenstown Basin, and merges into the Kawarau not far from the Arrow Bluff, and has here cut through the slate rock perpendicularly to a depth of about 200 feet. The Kawarau River is also fed in the Wakatipu Basin by the Shotover River, which takes its rise between Centaur Creek and Treble Cone. The Kawarau Gorge is filled with the same evidence of water and ice action as the Dunstan Gorge. It will be remembered, that till we reach the level of the Wakatipu Lake we have been steadily ascending, and in both the Cromwell and this basin, as we progress, we advance against walls of terraces that continually rise on the horizon to our view, and these on our return journey entirely disappear, or rather no such appearance is observable, from which circumstance I presume, that the weight of water pressing downwards has swept all before it, and prevented the formation of any such accumulations to form this terrace appearance, these terraces being composed entirely of drift.
In the Dunstan Basin the same thing is observable. Starting from the Manuherikia township towards the upper watershed of the valley at Dunstan Creek, terraces are seen under the Dunstan Ranges, but I believe no corresponding formation on the other or lower side, bounded by Blackstone Hill and the Raggedy Ranges.
I am informed that the features of the Arrow and Shotover Rivers are precisely similar. From Queenstown the road to Skipper's Creek does not continue directly up the gorge through which the Shotover River passes, but traverses a high saddle, and joins that river near its junction with the Moke Creek. On either side of this river are what are styled upper terraces, flat areas of land, having a scarcely perceptible inclination towards the river, so that where the gorge or valley widens, some considerable breadth of such land occurs, so much as nearly a quarter of a mile in depth at places. I have been as far up this river as Skipper's Creek, which, but for the small quantity of
water, might also have been styled a river, in so far as the characteristics of its watershed or valley are concerned; these upper terraces are conspicuous here, and I believe many other creeks exist having the same distinct features. The heights of the different ranges of the hills (and mountains as we style their highest peaks) forming these watersheds, of course vary, and their sides are also irregular, presenting many precipices almost perpendicular, and slopes of not very acute angles, showing, in fact, so much unevenness and so many fissures, that I will rather leave you to imagine than attempt to describe them, bearing in mind that in places such as at the Remarkables and Mount Aurum, the schist rock has been pushed up to elevations of some 6000 feet. The appearance to me was as though, when being thus forced up from below to its highest peaks, the strata, from insufficient strength, became broken, and the sides of what would have been an even plane from base to summit were shattered, presenting an appearance very like waves of the sea when driven before a gale, or the teeth of a common hand-saw; the sides of the sections nearest the points of upheaval being precipitous in the extreme, and the others presenting a more gradual slope. It will readily be conceived that many thousands of streams exist in a chain of such mountains, the accumulated power of which must be very great. It may also be conceded that these converge towards a few points as they discharge themselves into the sea in the shape of rivers. The ages of these rivers have, by clever and experienced men, been read, or it has been attempted at least, and definite periods assigned to their existence. Assuming that a a river, in cutting the rock, leaves its distinctive mark, what age shall we give to the Shotover, when we find that it has cut through the hard slate rock to the extent of about 200 feet? This same feature is also very plainly shown where the Arrow joins the Kawarau, and where both these rivers appear to have cut, perpendicularly, fully the same depth through a hard metamorphosed slate rock. The level of the Wakatipu Lake is 1000 feet above the sea; Cromwell, about 800 feet; Dunstan, about 600 feet; Teviot, about 400 feet; the Beaumont, about 150 feet.
Having now travelled to nearly the highest ground in the province, I have to make a hurried sketch of the country over which we have passed, skimming as it were in my return journey, over the tops of the hills and ranges, along the bases of which we have so far progressed; their heights vary from 7000 feet at Mount Aurum, to about 700 feet at the Coast Ranges. Mount Aurum, the ranges on either side of Skipper's Gully, and down the Shotover, till arriving at the Wakatipu Lake, present well-defined peaks, and the view from Queens- town embraces many such features; the Remarkable Peak affording a notable specimen. Another feature, however, is also here abundant. Hills and ranges of considerable elevation, say 1500 or 2000 feet, no longer retain those peaked or sharp featured characteristics, but are rounded off, and the sides ground down, smoothed and striated. This new feature I attribute to the
action of ice during what is called the glacial period. Proceeding down the Kawarau Gorge, through the lower end of the Cromwell Basin, to Dunstan and Manuherikia, almost all traces of the sharp peaked features are lost, rounded slopes being the most observable, with river cuttings and deep furrows scored in the sides of the Dunstan and Carrick Ranges. In continuation with a third feature, so distinctly marked as to have produced in the minds of the first explorers evidently a very strong effect, we find the various ranges at the lower side of the Dunstan, Ida Valley, and Maniototo Plains or Basins, called respectively the Raggedy Ranges, Blackstone Hill, Rough Ridge, and Rock and Pillar, the journey of about one and a-half days by the short road from the Manuherikia, nearly to the West Taieri, is, in fact, over almost a continual Raggedy or Rock and Pillar road, varied by creeks, gullies, and deep ravines, having anything but euphonious names conferred on them by the diggers,— the almost rounded hills being surmounted by rock, sometimes worn into the most fantastic shapes and life-like figures, till the Taieri is approached. The extraordinary features of this district may be judged of by the pictures in our Provincial Museum, and diagrams showing upper terraces of the Shotover, and the different features here alluded to.
The rough excrescences that led to the above names, are not so observable more immediately down the Molyneux Valley, as far as the Beaumont, where the road is no longer kept by the river side, and which point is about twelve miles from Tuapeka. This valley, the same as the Dunstan and Kawarau Gorges, bears ample evidence of ice action. From Tuapeka to the Woolshed, near Tokomairiro, for a short distance along the short road, the knobby appearance of the hills has entirely given way to smooth rounded hills, so that at the latter places the precipices and sharp peaks which we began with at Skipper's have entirely disappeared. I attribute these Raggedy and Knobby Ranges also to the action of ice, and regard these large fantastic masses of rocks as the parts of the peaks last left by the ice. The only occasional observable roughnesses I have examined on the latter rounded hills, consisted of large accumulations of cement, of different textures, colours, and components, which in places cover very considerable tracts of country; and I have found the same to a limited extent also on the Peninsula, in Dunedin Harbour, together with striated stones.
Down the Molyneux Valley are also to be seen very marked evidences of the action of water, to heights of fully 20 to 40 feet above the present level of the drift forming these valleys, on faces of rocks pointing up country—from which I imagine the flow of water during the glacial period, (when no material absorption by the earth could have taken place,) in warm seasons at least, very far exceeded that of the present day.
I must now proceed to notice this ice period, and try to realize its effects, and for this purpose ask you to remember the pictures that at different times
we have seen so well represented by our New Zealand artist, Mr. Gully, in his delineations of Mount Cook. The whole upper country is there represented as clothed with snow; and perhaps some of those present will remember its description by Drs. Hector and Haast, in the course of their explorations. I make these appeals to our own districts and residents, in order that, if possible, we may all realize the subject as of common and everyday interest. We will suppose that at some considerable height, on a range forming part of the watershed of a valley, we are travelling on this snow at night, when in the absence of the sun for some hours in such a bleak region, this may be done in safety: the crust of the snow will be of sufficient hardness to bear us, and but for the unevenness of the surface our journey might be performed in comparative comfort. As the day breaks, however, a change takes place: the snow, before crisp, will no longer bear our weight, a partial thaw setting in with the heat of the sun, we should sink in some places a few inches, in others one or two feet, and where the wind in drifting the snow would have almost bared high peaks and points of the rocks, the sun would melt the snow, and running water would be visible; the intense cold, however, of many feet of snow a few yards down the sides of the valleys would soon re-absorb the water, and the whole be turned to ice. Accumulations of snow would be made with the changes of the seasons, and these, in summer, would become partly rotten, or not of the solidity they were when first deposited, producing avalanches, which, in falling down, would of course, to a partial extent, displace small and large pieces of rock, which the frost would have acted upon and loosened; it will thus be seen that the valley gradually becomes filled with a mixture of snow and ice and stones—in short, a glacier. We will presume that this valley is of considerable length, and varying in width, that its contents (the glacier) move at the rate of about four feet in twenty-four hours. Such a powerful agent as would be represented by a glacier say of at least 4000 feet thick, as might be assumed existed under the Remarkable Range, would, whe in its advance to the sea coast, by its enormous weight, break down, grind, and score the rocks over and by the sides of which it travelled; and when this system or ice period changed, we might look for its refuse in the shape of stray strange stones, abroad in the country, as its influence dried up—as, in short, we find in our own case from the coast to Mount Aurum.
So far as our knowledge extends as yet into this glacial period, its normal condition would appear to have been that of a steady advance from the highest peaks to the coast line, accompanied in its course by vast volumes of running water. The existence of this water, owing to heat of the sun and internal heat of the earth, as evidenced by hot springs and active volcanoes, presents an anomaly in this otherwise frozen period; but as the state of the earth and its atmosphere to-day is such that we find the heat, at some considerable number of feet high—say, at least, 2000 feet in this province—sufficient to
prevent accumulations of snow, it will be sufficient in this paper to assume the number of years during which this change was being effected, to have been of sufficient duration to have deposited the beds of drift we are considering. For a more graphic description than I can give of the vast power exhibited by the ice during this period, I must refer to the interesting work entitled Frost and Fire.
The wonderful power of ice I will not attempt to dilate upon or try to picture further. I will now ask if it is not possible to reconcile it with the features exhibited in the Queenstown, Dunstan, and Manuherikia Valleys, would the ice and its accompanying waters there sweep over all the lower side in its journey to its point of discharge—viz., the sea coast, and prevent in its pressure all appearance of any terrace formation, form the rounded hills at Queenstown, and what were formerly peaks of the Raggedy, Blackstone Hill, Rough Ridge, and Rock and Pillar Peaks, into fantastic shapes, and cover with its debris the lower spurs and convert them into rounded slopes, as we find them in the immediate neighbourhood of the Taieri and sea coast.
If I have carried you with me so far, I will ask you now, if there must not have been old main glaciers or river beds. Evidences exist in our midst of the activity of ice at one time, and though I have not yet seen shoulders of valleys and escarpments of rocks striated, I have found, in abundance, pieces in the shape of striated stones detached from these points, both in Dunedin and its suburbs, at the Peninsula, Green Island, and in a valley under Mount Watkin, at Waikouaiti; in each case on faces of elevation pointing up country. Specimens found in Dunedin, at the back of the Acclimatization Society's Grounds, are on the table before you. I will also direct your attention to the specimens of light-coloured cements, which I chipped from blocks of various sizes weighing from several tons to a few pounds, and which are to be seen lying on the surface of the schist formations extending along the Ida Valley, down the whole length of the valley of the River Molyneux from Cromwell to Waitahuna and the Woolshed, at Tokomairiro. At Moa Flat they are a considerable height up the ranges, and bear the appearance of having been but lately deposited. The brown-coloured cement I have seen in the Shag Valley, at Mount Watkin, and along the lower spurs of ranges at the West Taieri, in addition to large accumulations at Waitahuna and the Woolshed.
If we find signs of activity in the drift on our basins, as we traverse them from Queenstown through Cromwell, Dunstan, and on to the Taieri, I think we may fairly assume that we have what we desire, old river beds or deep leads. In each of these basins, I find the drift in them in bands or stratified, not lying promiscuously. Had the basins been each independent lakes, we might have looked for greater evidences of stagnation in the drift than I think is shown at present. Supposing, for instance, I tip from a dray a load of gravel, on cutting through it perpendicularly, no distinct pattern is observable;
it is a well mixed heap; and this I imagine would be the case with a gradual denudation or deposition from the surrounding ranges of these basins, had such denudation been precipitated into stagnant water, such as a lake would represent. Each mass or particle in falling would be precipitated irregularly, and present a homogeneous appearance; but upon placing a further quantity on the heap, and playing water on it for a time—performing these last two operations many times, and again cutting the heap in two—it will be seen that the parts influenced by the active water bear a distinct pattern. It will be stratified or appear in bands, and so agree with the deposits I have alluded to, which uniformly present this appearance of active aqueous action.
It is so at the upper terraces on the Shotover; at the big beach in the Queenstown Basin; the banks of the river at Cromwell, 75 feet deep to the present water level, bear the same appearance; and it is again repeated in the drift cut through by the Molyneux, through the Dunstan and Teviot Basins to the Beaumont, through the length of the Manuherikia Valley, and, I presume, down the Strath Taieri or Taieri Valley, though down this I have not been; at a considerable elevation up the spurs at Hyde Diggings, and at Dunstan Creek, at which latter place, in the claim of the Mountain Race Company, these bands, sometimes two or three feet thick, are elevated from the plain at an angle of about 45 degrees. The conclusion I came to afer my hurried inspection was, that at one time there had been an outflow towards the Canterbury Province. But from a later upheaval, which would be shown in all likelihood by basaltic formation in the neighbourhood, these bands have been transferred from the level position in which I imagine they had been first formed, to their present position. This conclusion may be erroneous, as, whilst inspecting this claim in the depth of winter, two years since, a snow storm with fog came on, that compelled us quickly to return. An intelligent, and I may add very active, storekeeper, who was my guide, informed me that the deeper they went the better gold they were finding. It was a hurried inspec tion, and as hastily formed an opinion. The greatest elevation of the part of this ground worked was about 70 feet; below this depth they could not get a fall for their tailings, unless at considerable outlay in extending their tail-race. Within a few miles of the Woolshed, by Tokomairiro, at a new claim opened among the rounded hills, I found the same sign of active aqueous action.
At Maruwhenua, I am informed, the drift lies in distinct bands. At Dunstan, when the Fortuna Mining Company sunk to a depth of 109 feet without bottoming, and abandoned on account of the West Coast rush, the drift was found in bands. At Black's No. 3, very rich payable dirt was found at a depth of about 150 feet. At Mount Ida, in the Hogburn, a shaft was abandoned after sinking about 80 feet; at Waitahuna, the same, after sinking about 100 feet, not reaching, in either case, a proper bottom. At Wetherstone's Flat, at 432 feet, no result has been obtained, some asserting one thing and some
another; statements alternately being made that payable washdirt for the last 20 feet existed, and of an utter absence of the precious metal. This flat, in fact presenting a surface, I believe, for I have not been there, of not two miles square, and, in proportion to the large basins up country, most unfavourable to determine the existence of an old river channel. It is in the heart of most hilly, and I might say almost mountainous, country, and the shaft in question being sunk near the centre of the basin, would not afford indications or results such as I imagine may be proved by testing an outflow or inflow of one of the larger basins I have already alluded to.
The extent of the gold fields of this province has been given in the Government maps. If the wearing power I have attempted to describe is correctly stated, we should surely possess far richer spots than those yet worked, assuming that the rottenness of this vast range of country at present fills the different basins.
In concluding, I beg to thank Mr. J. T. Thomson, our Commissioner of Crown Lands, for assisting me with his experience in reference to ice evidence in Scotland, and in our explorations through Green Island.