THE LAKES IN OTAGO PROVINCE.

Westport Times, Volume IV, Issue 696, 11 August 1870, Page 2

THE LAKES IN OTAGO PROVINCE.

The following are extracts fron a paper recently read by Mr M'Kerrow, before the Otago Institute :—■ " The lakes of Otago belong principally to the two great river systems of the Clutha and Waiau. Lakes Hawea, Wanaka, and Wakatipu, belonging to the Clutha river, and Lakes N. and S. Mavora, Te Anau, Manipori, and Monowai to the Waiau river. These lakes are of great extent relative to the size of the country. Taking their dimensions from the reconnoisance survey, we have for the Clutha river system : Length Breadth Area Feet above sea Miles Miles Sq miles level Lake Hawea 19 3 48 1189 Lake Wanaka 29 1 to 3 75 974 Lake Wakatipu 50 1 to 3£ 114 1069 " For the Waiau river system:—■ Lakeg N. & S. n . . , . „„„„ Mavora 9 * to 1 5 2073 Lake Te Anau 38 1 to 6 ") Three western ( . arms Te Anau C l " b94 each 10 to 18 1 to 3 ) Lake Manipori 18 i to 6 50 597 Lake Monowai 14 £ to 1 11 500 " It may here be noted that the Te Anau is the largest lake of the Middle Island. The lakes are all known to be many hundreds of feet deep, but no great attention has been given to the sounding of any of them, excepting Lake, Wakatipu. Soundings of this lake have been taken by several persons independently. The greatest depth given is 1400 feet, about the middle of the lake off Collins' Bay, and sixteen miles from the south end of the lake. " The lakes all lie along the eastern side of the great western ranges or Southern Alps, as also lakes Ohau, Pukaki, and Tekapau, of the Waitaki river system, in Canterbury. The length of the lakes greatly exceed thoir breadth, and they all lie lengthwise in their valleys, and occupy the full width of the valley, the mountains generally rising from their shore line.

Their surfaces do not differ greatly in altitude above sea level, and what difference there is seems to have a relation to the height of the mountains —the lakes of the greatest elevation being in the valleys running down from the highest mountains. The lakes terminate just where their valleys begin to widen out into plains. Along their sides and at their southern ends there are invariably vast collections of shingle and large blocks of rock. From these similarities it is evident that some great natural cause or law has had a uniform action over this 300 miles of country in producing the lakes. An observer might be sorely puzzled to account for the origin of the lakes, but with the researches of such philosophers as Agassiz and Forbes as guides, it is plain that the glaciers, which now lie far up the valleys and ravines of the mountains, are, comparatively speaking, the puny descendants of glaciers, that formerly filled valley and lake beds with their vast dimensions, and in their slow but irresistible march, carried forward the spoil of the mountains, and deposited it as lateral and terminal moraines. " Accepting this explanation of the glaciers at one time filling the lake basins, the question arises: Did the glaciers excavate the basins, or did they simply occupy them for a time, as the lakes now do ? " In how far a glacier could excavate a valley out of rock, is necessarily a question very much of speculation. It will be of interest, however, to endeavor a general demonstration of the effect. In a paper read before this Society by Mr Beal, attention was directed to the wearing power of ice in motion, and to the rounded outline of the'hills so operated on. As an illustration of this action, Peninsula Hill near Queenstown was mentioned. This hill is 1700 feet above the level of the lake surface, or about 3000 feet above its bottom. If then we suppose that the glacier did not scoop out the lake bed, but simply smoothed its surfaces, it follows that there would be a glacier of from 3000 to 4000 feet in action. Now, can it be conceived that this vast mass slid over the bed of the present lake for a geological era, without working its bed deeper and deeper ? " We find on examining the beds of such rivers as the Kawarau and Shotover that running water, probably never even in the highest floods more than forty feet deep, can cut or wear channels through hard schist rock of 200 and 300 feet deep. If running water and the sand and gravel which it carries along, can produce such effect, it seems easy to arrive at the inference that a glacier, say 1000 feet thick, would with chips of rock adhering to its under surface, plane down its bed to a depth only limited by the duration of the process. " Although the Otago portion of the Southern Alps is from 6000 to 10,000 feet high, yet there are numerous saddles in them much lower, from which the valleys run to the West Coast on the one side, and to the Lakes on the other. The valleys on the Lakes' side act as funnels down which the winds blow and discharge their moisture. The effect of the discharge is seen in the forests which are invariably found in these valleys In several cases, where the saddle of the dividing range doe 3 not exceed 3500 feet above sea level, the forest is continuous from the west to the east side of the mountains. Thus, beginning at Martin's Bay and following up the Hollyford Valley to the Eglinton Pass, thence to the Te Anau Lake, and then down the Waiau Valley to the ocean, there is a continuous belt of forest, 160 miles in length, and with its ramifications covering upwards of a thousand square miles. It is worthy of remark that the forests of Otago are all to be found within the districts enjoying a moist climate. Thus on the west side of the Province there is the couutry between the West Coast and the Lakes ; on the east side there is the margin of thirty or thirty-five miles along the coast over which the eouth-westers usually extend. The highest ascertained limit above sea level of the forest is 3500 feet. " The comparatively dry interior districts, extending principally between the Clutha and Waitaki rivers have no forests, there have been, however, forests in the interior districts at one time. " If we examine any of the forests on the East Coast in their natural state, and before a litter of rejected timber and branches has accumulated in them, it seems difficult to imagine that a fire could make its way through them. But the forests in the Lake districts, and generally in high altitudes, are free from the tangled under, growth of the East Coast forests. In place of it, the soil has a covering of foggage and moss often a foot deep. In a dry season this readily ignites, and as it smoulders rather than burns, the work of destruction is very sure over the surface the fire extends. la this way a portion of the forest in the Te Anau district was destroyed some years ago, by a grass fire kindling the foggage. " Speaking of the Lake districts in» general manner, it may be observed that, considering the extent of agricultural, pastoral, and forest land that abounds in them, their mineral pro-, ducts, their delightful climate and extent of inland navigation, they hare; within their own borders all the raainj elements that render communitiel prosperous and flourishing.