The Waimakariri.

The Waimakariri, another of the important rivers crossing the Canterbury plains, next claims our attention. If we draw a straight line from Mount Greenlaw to the Hurunui saddle, the watershed along the central chain belonging to its hydrographical system is thirty miles long, thus being of greater extent than that of the Rangitata; however, the mountains at the head of the northern river are not so high, nor the snow-fields so extensive, and consequently the amount of water coming from the Southern Alps proper is not so considerable in the Waimakariri, although the Poulter and Esk nearly make up for the difference. In fact, although the hydrographical basin of the river is nearly twice as large as that of the Rangitata, and within a few miles of the same extent as the Rakaia, it nevertheless ranks third as to the amount of water it brings to the sea. The main source of the Waimakariri is a glacier at the head of the White river, having its origin in the snow-fields on the northern slopes of Mount Grreenlaw, 4162 feet above the sea-level. After receiving several tributaries of glacier origin, the White river, as it has been named from the peculiar colour of its water, generally thick from finely triturated matter, originating from the action of the glaciers on their rocky bed, unites five miles from its origin with the northern Waimakariri, which having a south-south-east course, meets the former at a right angle. That course is continued after this union of the two confluents, the valley page 213enlarging considerably below it, and receiving, four miles lower down, the Crow river on its left bank, having its glacier sources on the southern slopes of Mount Rolleston. A few miles above this junction, the valley already assumes the principal characteristic features of all our large alpine rivers, a wide shingle-bed about a mile broad, in which the river meanders in numerous channels. Six miles below the Crow river, the Bealey, at the head of which Arthur and Groat's Passes are situated, enters the main valley; and seven miles lower down, the Hawdon joins the Waimakariri on its northern, and the Cass on its southern bank. Respectively twenty-one and twenty-five miles from the junction of the north branch with the White river, two of its most important affluents, the Poulter and the Esk join the river, which from that junction had followed a general east-by-south course. It now turns sharply to the south-by-west, or in the direction of the valley of the Esk. After a course of eight miles, and still having a bed of about half a mile wide, with high terraced fiats on both sides, the Broken river joins it from the west, bringing the drainage from the Cragieburn range and the western slopes of Mount Torlesse. Before following the rivers through the gorge to the Canterbury plains, I wish to add a few words respecting the small lakes which still exist among the morainic accumulations, and lacustrine and fluviatile deposits in the district under review. In the first part, mention was made of the remarkable glacialized appearance of the country, and that after the retreat of the great glacier during the New Zealand Ice-period, a large lake had been formed, before the gorge which now passes between Mounts Torlesse and Puketeraki had been excavated. This lake became gradually filled by lacustrine and fluviatile deposits; but the glacier advanced again, excavated new channels, and deposited new morainic accumulations upon the older beds of similar origin; amongst these, several small lakes are still situated. Thus Blackwater, a small tarn, lies between the older morainic accumulations, protected by roches moutonnées, whilst Grrassmere and Lake Sarah are the last remnants of a lake of considerable extent, where now the Cass plains are situated; the moraines east of Lake Grassmere, crossing the valley, being, however, still well visible. Lake Pearson, on the other hand, owes its preservation to two large shingle-fans on the eastern and western ends, by which its bed has been protected. Lake Letitia on the northern, and Blackwater, and other smaller tarns on the southern side of the eastern portion of the terraced plateau, are small remnants of the old lake once existing here. Roches moutonnées and morainic accumulations are visible everywhere, rising above the general page 214level of the tableland, about 2100 feet in altitude. The Waimakariri, after having excavated its channel in this plateau of lacustrine and alluvial origin, then enters between the ranges, having on the northern side the Puketeraki range, and on the southern side Mount Torlesse. It has cut a deep picturesque gorge, the mountain sides on both slopes being covered with dense Fagus forest, through which no road has hitherto been constructed. For six miles, the distance measured in a straight line, the river winds through the gorge, running nearly south, after which it enters the Canterbury plains. Flowing about 300 feet below the level of the latter, the Waimakariri now assumes the character of a broad shingle river, and receives, after a course of two miles, the Kowai, which is its last affluent. For 41 miles the river flows through the plains, being again retained in narrow rocky banks at the lower gorge, four miles and a half below the junction of the Kowai. This gorge is about a mile long, the river, instead of lowering its bed through the alluvial deposits on both sides, having cut its way through the hard palæozoic rocks, of which the isolated Gorge hill consists. The slope of the plains in these upper and middle portions, being greater than the gradient of the present river-bed, the high terraced banks, which hitherto accompanied the river-bed, disappear about 12 miles from the mouth of the river, and the lower delta of the river is reached, which, as I have already shown in my report on the formation of the Canterbury plains in 1864, is still being formed by the river, which if not checked by artifical means will shift its channel in course of time as the deposition of alluvial beds advances.