The Province of Otago comprehends all that part of New Zealand south of the river Waitaki and a line from Lake Ohau through Mount Aspiring to Big Bay on the West Coast, and it contains, with Stewart Island, an area of about 20,876 square miles. It is essentially a mountainous country, the only very extensive flat land being the Southland plains, between the Hokanui and Moonlight ranges and the sea. Besides these, however, there are many smaller areas of flat or undulating country, and in the interior the Maniototo Plains, the Idaburn Valley, and Manuherika Plains are of considerable extent.

The highest land in the Province is situated in the north-west corner from Mt. Aspiring (9940ft), through Mt. Edward (8459ft), Mt. Tyndall (8116), Mt. Ansted (8157ft), Centaur Peak (8284ft), Cosmos Peak (8000ft), and Mt. Earnslaw (9165ft), to Mt. Christina (8475). Southward and eastward of this the mountains lower until they assume, towards the sea, with few exceptions, the form of rolling downs, averaging about 1500 feet above the sea level. Along the west coast, however, the mountains never lose their rugged character, and maintain an altitude in the highest peaks of between 4000 and 5000 feet as far as the south-west corner of the Province.

Sounds.

Along the western seaboard these mountains are penetrated by long winding sounds, or fiords, which are of great depth, but universally become shallower at their entrance into the sea. Not much is known yet as to the actual depth of these sounds, most of the soundings recorded giving no bottom at depths of from 150 to 900 feet. The deepest soundings on the chart are 1728 feet in Breaksea Sound off First Cove; 1500 feet in Thompson Sound, off Deas Cove; and 1284 feet in Milford Sound, off the Stirling waterfall. Bligh Sound seems to be the shallowest, the greatest depth being 468 feet, unless it be Preservation Inlet, where the greatest depth recorded is no bottom at 336 feet.

The entrances to most of the sounds vary in depth between 150 and 280 feet, the exceptions being Preservation Inlet with a depth of only 14 to 84 feet, Milford Sound with a depth of 360ft, Doubtful Sound with a depth of 372ft, and Thompson Sound with a depth of 456ft. But of these, Doubtful Sound, although 372ft deep at the entrance, shallows to 150ft on either side of Banza page 6Island, so that, with the exception of Preservation, Thompson, and Milford, all the sounds have at their entrance an average depth of 215ft, with a limit of variation more or less of 65 feet.

The mountains that surround Preservation and Chalky Inlets are rounded in outline, and comparatively low, the sides being covered with bush down to the water’s edge; but from Dusky northwards, high, almost perpendicular, cliffs are often seen, until in Milford Sound the land rises abruptly from the water in precipieces 1500ft high (see frontispiece). These steep cliffs are, however, confined to the interior of the sounds, for the sea coast is nowhere high, but falls with a comparatively gentle slope nearly to the sea level. See fig. 21.

Lakes.

On the inland side of the west coast range the place of these sounds is taken by the arms of the Lakes Te Anau, Manipori, Monowai, and Howloko; and so far do these fresh water arms on the east and salt water sounds on the west penetrate into the heart of the mountains that in several places they approach to within nine or ten miles of each other.

To the north-east lies Lake Wakatipu, and further on in the same direction Lakes Wanaka and Hawea. These lakes present scenery unsurpassed probably in the world, for, unlike the Swiss lakes, they do not lie outside the principal mountain masses, but wind themselves close round their feet. Wanaka, which is perhaps the most beautiful lake in the world, and Wakatipu show glorious views of snowy mountains, to which Lucerne and Brienz cannot aspire. The great length of Te Anau in a straight line (38 miles) with the shoulders of the mountains, coming down one behind the other, gives a view totally unlike anything in Switzerland; while Manipori is dark and stern, but relieved by the green islands dotted over its surface.

Not much is yet known of the physical geography of these lakes, but what is known will be found in Mr. McKerrow’s paper in the third volume of the ‘Transactions of the New Zealand Institute.’ Lake Wakatipu is the only one that has been sounded, and its greatest depth is said to be 1400ft, which is about 400ft below the level of the sea. This feature, however, is by no means peculiar to the lakes of Otago. All the large lakes of North America, except Lake Erie, and several of those in Italy, descend below the sea, while Loch Lomond, in Scotland, is 600ft deep, and only 20ft above the sea level.

The water in the southern half of Lake Wakatipu is as blue as the Rhone at Geneva, but near the head it turns a pale, milky colour, owing to the fine mud brought by the Dart and Rees from the glaciers of Mount Earnslaw and Cosmos Peak. In many places terraces fringe the lake, which prove that the water once page 7stood higher; but around the greater part these are absent. These terraces are generally found at the embouchures of the large streams, and owing to the steepness of the sides of the lake, no deposit is now forming at other places; so that these gravel beds are not continuous, and do not extend across the lake, although they are at the same level on both sides. Ultimately, however, as the lake fills up, they will be all connected.

The arms of Lake Te Anau and Manipori exactly resemble the sounds on the West Coast, and although the other lakes do not show the same abruptness of outline, still the valleys of the streams in the neighborhood have many analogies with the sounds. For instance, the Shotover River has no falls nor rapids in its course, but has cut a narrow gorge in the solid rock to a depth of about 200ft. (See fig. 16.) All the larger lateral streams have also cut down their channels to the same level, but some of the smaller ones enter the gorge by falls, just like Milford Sound. Again the gorges up the Routeburn are perpendicular and rough, exactly like those of the West Coast sounds in miniature. But away from the western mountains the scenery is quite different, and high, perpendicular precipices give way to gentler slopes and more rounded outlines.

Rivers.

All the rivers and nearly all the creeks in Otago are rapid streams, running over shingly or rocky beds. Like all mountain rivers they are liable to considerable fluctuation in level, a subject which in the case of the Taieri has been ably treated by Mr. J. T. Thomson, C.E.^* and Mr. G. M. Barr, C.E.^† Mr. Thomson also, in another paper,^‡ has a very important discussion on the curves formed by the beds of the rivers Manuherikia, Waitaki, Shag, Taieri, Clutha, Cardrona, and Mataura, all of which he shows conform practically to the curve of the ellipse. This result is contrary to the general belief of geographers, who consider that the parabola is the curve which a river tends to assume from its source to its mouth. Mr. Thomson, however, considers that rivers tend to assume the curve of the ellipse only when they are hollowing out their beds, and that when they are raising them they tend to assume the curve of the parabola,^§ but he offers no explanation of the cause of this difference. The Mataura is the only river in New Zealand with falls near its mouth.

Plains.

The Southland Plains have already been mentioned. They have a length of nearly forty miles with a breadth of about twenty-page 8six miles. A remarkable circumstance connected with these plains is that they are continued up the valleys of the Mataura, Oreti, and Jacob Rivers, and wrap completely round the hills that properly bound them inland, so that we might consider the Southland Plains as extending up to the Five River Plain, Long Ridge, and the Pyramid, out of which the Moonlight Range and Hokonui Hills stand like islands.

With the exception of the Waitaki plains and Inch Clutha, at the mouth of that river, all the other plains in Otago lie inland. The principal are the Maniototo plains, 28 miles long, and with an average breadth of about 10 miles; Idaburn Valley, with a length of 25 and a breadth of 4 miles; Manuherikia plains, with a length and breadth of about 35 and 4 miles respectively; and the Upper Clutha plains, with a length of 33 miles and an average breadth of about 5 or 6 miles. Plains of smaller extent are found in many other places, as at Strath Taieri, Lower Taieri, Tokomairiro, Tapanui, Moa Flat, &c. A considerable extent of land, some 70 miles in length by 20 in width, stretching from the Shag river between the Rock and Pillar and Silver Peak hills, through Waipori and Lawrence to the Clutha, may be considered as an elevated plain or plateau, some 1500 feet above the sea, and deeply cut through by the streams that cross it.

Mountains.

The distribution of the mountain ranges in the Province is very irregular and complicated; but to assist the memory of those who are not personally acquainted with the country, I may compare them roughly to the fingers of the right hand widely spread out, but with the first and second fingers approximated, and with the palm resting in the south-west part of the Province of Canterbury. In this case the thumb will represent the Hawkdun and Kakanui mountains, running north-west and south-east, which form the southern boundary of the valley of the Waitaki. The first finger will represent the Dunstan and Lammerlaw Ranges, running more or less north and south, which form the eastern watershed of the Clutha. The space between this finger and the thumb contains the large inland plains and the winding valley of the Taieri, and it is crossed in a south-west and north-east direction by four ranges, which lie at right angles to the general run of the mountains. These are Raggedy Range, Rough Ridge, Rock and Pillar Range, and the Silver Peak hills. The second or middle finger will represent all that rugged tract of country between Lakes Wanaka and Wakatipu, called the Harris and Richardson mountains, continued southwards in the Remarkables, Garvie mountains, Obelisk Range, and Umbrella mountains, and running through the Kaihiku mountains to the sea at Nugget Point. It is bounded by the Clutha on the east and the Mataura on the west. The third or ring finger will represent the page 9Humboldt mountains, the Thomson and Livingstone mountains, the Takitimus, and the Longwood range, having a general N.N.E. and S.S.W. direction, and lying between Lake Wakatipu and the Oreti river on the east, and the Hollyford river, Lake Te Anau, and the Waiau on the west. Between this finger and the middle finger lie the Southland plains, bounded on the north by the Hokanui and Moonlight ranges, which run in a north-west and south-east direction, or nearly at right angles to the general trend of the mountains. And last, the little finger will represent the west coast range running in a north-east and south-west direction.

Coast Line.

The eastern sea board of the Province is formed generally by low hills and sandy beaches, interrupted by bold headlands where the harder rocks run out to sea. On the south, low cliffs run from the Nuggets to Preservation Inlet, except between the Mataura and Jacob rivers, where the Southland plains form the coast line. As might be expected the sea deepens more rapidly on the west coast than on the east, but contrary to expectation the south coast is shallower than either. The 100 fathom line keeps at an average distance of 25 miles from the east coast as far as the Nuggets, when it sweeps away south and includes Stewart Island and the Snares. Along the west coast little is known, but the depth seems variable. Foveaux Strait is nowhere more than 25 fathoms in depth, and an elevation of 130 feet would join Stewart Island on to the main land.

Comparison between the New Zealand and Swiss Alps.

No one, I think, who after visiting the Alps of Switzerland should explore the Alps of New Zealand, could fail to notice two remarkable points of difference between these mountain regions The one is that mountains with sharp serrated summits, which [unclear: are] the exception in Switzerland, are the rule in New Zealand, and the other is that the numerous large waterfalls, which the traveller in Switzerland sees at almost every turn, are quite exceptional in New Zealand. A few waterfalls, but they are very few in comparison with Switzerland, are found in the deep fiords on the west coast, and a few smaller ones towards the heads of the valleys in the heart of the mountains, and these are nearly all. And yet the mountains in New Zealand are quite as rough and rugged as the Alps of Europe, and, indeed, the gorges are more numerous and deeper. There are also other minor points of difference. The passes in New Zealand are lower, and the mountains are in places much more covered with loose debris than any part of the Swiss Alps. But this last is a local peculiarity, and is not so noticeable in Otago as in Canterbury and Nelson.

Two theories may be put forward to explain these differences. One is that the New Zealand Alps are composed of rocks which page 10suffer from decay and degradation much more than the rocks that compose the Alps of Switzerland. The other is that the mountains of New Zealand are of far greater antiquity than the Swiss Alps, and have in consequence suffered a far greater amount of denudation. To any traveller in New Zealand who had limited his explorations to the Province of Otago, east of the great lakes, the first is the theory that would most naturally present itself to his mind, for all the mountains that he would have examined would have been composed of mica schist. But in the west of this Province the mountains are composed of hard gneiss, crossed by dykes of eruptive rocks; and further north, in the provinces of Canterbury, Nelson and Marlborough, the mountains are chiefly formed of sandstones and slates, as hard on the average as the rocks composing the Alps of Switzerland, and yet the phenomena that I have mentioned are quite as noticeable in those provinces as they are in Otago. On the other hand we have proofs in the geologlcal structure of our mountains, as I shall presently show, that the New Zealand Alps have been constantly exposed to the action of rain and wind ever since the jurassic period, and that many of the larger valleys had been cut down nearly to their present depth in the eocene period, a time when the European Alps and the Himalayas were only just rising above the sea. Probably, therefore, the second theory is the more correct, but the first may reasonably be called in to explain local details.

Peculiarities in the Physical Geography of Otago.

Another remarkable fact in the sub-alpine part of Otago, o[gap — reason: illegible] that portion which lies eastward of the great lakes, is that most of the larger rivers do not run in what we must consider as their natural channels, but constantly cross abruptly from one valley into another. For example, the Clutha, after arriving at Cromwell, ought to have continued straight on and joined the Frazer instead of cutting through the Dunstan Range. Lake Wakatipu should have emptied itself at Kingston into the Mataura, which, in its turn, instead of breaking through the gorge at Athol, should have continued by the Dome pass to the Five-river Plains, and there have joined the Oreti. The Upper Taieri and the Idaburn should have joined the Manuhirikia at Blackstone Hill. The Lower Taieri and the Tokomairiro should empty themselves into the Clutha near Kaitangata; while the Pomahaka should have joined the Mataura instead of the Clutha.

While also the larger rivers run almost always in narrow gorge-like valleys, many of the large valleys have but very insignificent streams flowing in them. Such, for example, are the Idaburn valley, the Manuherikia valley, the Tokomairiro plains, and the Waimea plains, which last are but a portion of the valley running from the Upper Oreti to Port Molyneux. The Taieri plains also page 11do not properly belong to that river at all, for they run up the valley of the Silverstream, while the Taieri breaks suddeuly in upon them by a lateral gorge. These plains are really the valley of the Silverstream, which the Taieri has usurped.

It is these anomalies that physiography, or surface geology, undertakes to explain; and the explanation when obtained is not only curious and interesting, but it is highly important from a practical point of view; for it informs us of the successive oscillations in level that the land underwent while the surface features were being formed; and on these various oscillations of level the mode of deposition of the different river alluvia depends. But as some of these alluvia contain gold, it is evident that anything that throws light on their mode of deposition is of great importance to the alluvial gold miner.

Before, however, trying to explain the surface geology of the Province, it will be necessary to describe its geological structure, for unless this is first clearly understood, great and important errors are sure to get into our theories of the surface geology of the country.