Billeder på siden
PDF
ePub

scraped the barren hillsides, and from the scrapings have made the fertile plains that produce food for man and beast. Not only have they done these great works in the past; they are doing them now as well, and doing them right at our doors, where the children can see the work being carried on from day to day. The teacher who fails to call attention to the relation of the forms of land and water in the home neighborhood to the natural forces still at work there sins against his pupils, if not against his own soul.

ILLINOIS STATE NORMAL UNIVERSITY,

HENRY MCCORMICK.

NORMAL, ILL.

THE YUKON DISTRICT.

By the recent discovery of remarkably rich deposits of placer gold in the Yukon basin much attention has been directed to the northwestern portion of our continent and any information concerning that region is eagerly sought. As a result the papers are filled with the most astonishing mixture of fact and fancy, all of which finds ready credence. It is difficult to separate the truth from the fiction, but one who has a clear idea of the more important geographic features of the region can at least tell what is possible or probable. Numerous recently published maps, all more or less inaccurate, have made the outlines of the land and the drainage systems fairly familiar, but the relief is rarely represented, except in the crudest fashion. Hence this most important physiographic factor is the one least known. But the mineral and other resources of the region and the peculiarities of its climate, especially the distribution of rainfall and range of temperature, depend directly upon the disposition of the mountain ranges, and therefore an account of the region from any point of view should begin with an account of its orography.

The dominant physiographic features of the Yukon district may be apprehended best by starting with a section through a much better known region. Crossing the continent by the Canadian Pacific railway, the Rocky Mountain range is first encountered rising abruptly from the western margin of the Great Plains. Passing this a plateau belt, something less than 500 miles in

breadth, is traversed, on the western margin of which is the Coast range, the northward extension of the Cascades. Still further west is another range whose partly submerged summits form the islands fringing the Pacific coast. Finally, rising from the surface of the high plateau between the Rockies and the coast, are several less continuous mountain groups, the most important of which are the Selkirk and Gold ranges. The characteristic features of these several mountain ranges have been admirably described in an article on "The Canadian Alps" by Professor Fay, published in the June number of this JOURNAL. Briefly summarized, then, the dominating orographic features in British Columbia are a broad mountain-rimmed plateau from which rise shorter ranges with a partly submerged range forming a fringing archipelago. All of these features, more or less modified, may be traced far to the northwest, through the Yukon district, in the British Northwest Territory and Alaska.

The Rocky Mountain range extends northwestward with about the same trend that it has in British Columbia, nearly to the Arctic ocean, and thence, with greatly diminished altitude, continues westward to Bering sea, parallel with the Arctic coast. In general it forms the continental divide, though two rivers, the Peace and Liard, head upon its western side and flow eastward across it to the Mackenzie.

The Coast range continues northwestward through British Columbia for some distance parallel with the Rocky Mountains, but more quickly bends westward, following the curve of the North Pacific coast line. At the head of Lynn Canal, in southern Alaska, it ceases to be a coast range, passing behind the St. Elias Alps, which here take its place next the coast. It extends a short distance into the interior and then merges gradually with the interior plateau. Throughout its entire extent, but particularly in its northern portion, the Coast range does not possess a distinct crest line, but is rather a narrow belt of deeply dissected plateau. The breadth of the belt is nearly 40 miles through the eastern margin, where it merges with the interior plateau, but is not well defined. The few rivers which cross it flow in narrow canyons, once much deeper than now, their lower portions being occupied by deep fiords which are being rapidly silted up. The canyon walls are

very steep, though rarely precipitous for 5,000 or 6,000 feet from the river, while above this is a rolling upland with a great number of peaks rising to a uniform altitude of about 8,000 feet. Looking westward from a summit near the coast, the closely crowded peaks form an even skyline which strongly suggests the presence of a deeply dissected baselevel plain. The coastward portion of this upland, where the precipitation is heavy, feeds numerous glaciers, some of which reach tidewater. The interior margin is at present free from glaciers and nearly free from permanent snow, but bears the marks of recent extensive glaciation.

The St. Elias range has the form of a crescent, embracing between its two horns that portion of the North Pacific sometimes called the Gulf of Alaska. The eastern horn, partly submerged, forms the Alexander archipelago and continues southward with more or less extensive breaks through Queen Charlotte and Vancouver islands, where it is called the Vancouver range by Dawson, to the Coast range in Washington and Oregon. The western horn of the crescent, also partly submerged, forms the Kenai peninsula and Kadiak island. The central portion of the crescent, between Cross and Prince William sounds, forms the culminating point of North America with at least two peaks, St. Elias and Logan, and probably others, rising more than 18,000 feet above the sea. This range, particularly its central portion, is very different in character from the Coast range of Southern Alaska and British Columbia. It is composed largely of rocks formed in very recent times, in the age known by geologists as Tertiary, and, according to Russell, some of the precipitous mountain faces have been formed by the breaking or faulting of the rocks whereby great edges have been exposed, as are the edges of ice blocks in a stream after a winter breaking. If this is the case its angular, rugged forms are, to some extent at least, due to the original structure rather than to the sculpturing of erosive agents. Little changed since its formation, the range thus bears the marks of extreme youth, while the Coast range as certainly by its topography shows its great age.

Passing behind the western end of the St. Elias range, as the Coast range passes behind its eastern end, is another range whose southern portion forms the Alaskan peninsula and the Aleutian

islands. It is characterized by a large number of volcanic peaks, many of which are still active. Mt. Wrangell, 130 miles from the coast, may be regarded as the easternmost of the volcanoes belonging to this system. But little is known concerning the northern portion of this range, for it occupies the least explored portion of North America. Some mountains even higher than Mt. Wrangell are said to lie between the Kuskoquim and Yukon rivers, but the information concerning them is meagre and unsatisfactory.

The interior plateau belt of British Columbia expands toward the northwest as the marginal ranges gradually diverge. Its southern portion is drained by lateral streams, the Frazer, Masse, Stikine and Taku flowing to the Pacific, while the Peace and Liard flow east to the Mackenzie. North of the sixtieth parallel, however, the marginal ranges are unbroken and the expanded plateau between them forms the great Yukon basin. There are no highin this region except the rivers, so that while most of these have been traversed and mapped with a fair degree of accuracy, so great are the difficulties of overland travel that little is known of large interstream areas.

ways

An appropriate and convenient name for this great upland is the Yukon Plateau. Its general altitude at the divide between the Taku, the Liard and the southern branches of the Yukon is about 5,000 feet. So far as known it retains this elevation along its southern margin at the base of the Coast and St. Elias ranges, but slopes gradually northward and westward to less than 3,000 feet near the axis of the basin. Thence it rises again, but less rapidly, northward to the base of the Rocky Mountain range. Only in a general way can this highland be regarded as a plateau, for when considered in detail much of its surface is extremely rough and broken. The larger streams have sunk their channels from 1,000 to 3,000 feet below the general plateau level, and most of them have opened out rather broad valleys wherever they have encountered soft rocks. The smaller streams in their lower courses flow in narrow, V shaped gorges, while their head branches often occupy high, broad valleys which indicate an old lowland formed near the former level of the ocean. A recent uplift has given the streams new vigor and thus the valleys are in part old

and in part young. Above the general plateau level rise many rounded, dome-like summits and a few sharp peaks. These sometimes form considerable mountain groups corresponding to the interior ranges of British Columbia. The most extensive is perhaps the Cassiar range, east of Lake Ahklen, though others nearly as important are known to occur elsewhere on the Yukon plateau, but have not yet been mapped or named. Most of the mountain ranges which appear in various parts of the Yukon basin on some maps of the region are simply portions of the plateau which have somewhat the appearance of distinct ranges as seen from the rivers. When seen from the proper elevation their summits fall nearly in line with the general level of the undulating upland.

The western margin of the Yukon plateau touches Bering sea at a few points, though it is generally separated from the coast by a belt of tundra of varying width. This is a level, treeless lowland, only a few feet above the sea and dotted with innumerable lakes and ponds. The confluent deltas of the Yukon and Kuskoquim, in southwestern Alaska, form the largest area of tundra in America.

The Yukon drainage system occupies the greater part of the mountain-rimmed highland basin above described. Its trunk stream is symmetrically located, receiving tributaries of about equal number and size from either side. Considerable diversity exists in the nomenclature of the rivers in the upper part of the basin, and also some difference of opinion as to which should be considered the trunk stream and hence the true source of the Yukon. From a consideration of the physiography of the basin, its main axis must be regarded as coinciding with the Ahklen valley. Unfortunately another usage is too well established to permit the application of the name Yukon up to the lake, as has been attempted in some publications. This subject has been somewhat fully discussed elsewhere and the following conclusion reached: "The name Yukon is applied to the river from its mouth to Selkirk. The name Pelly is confined to what has been called the "Upper Pelly,” i. e., from Selkirk to its head. The name Lewes is applied to the river from Selkirk to Lake Lindemann, called the "Yukon " by Schwatka. Finally the river flowing from Lake Ahklen is called

* An expedition through the Yukon district, C. W. Hayes, Nat. Geog. Mag. Vol. IV., 1892, p. 133.

« ForrigeFortsæt »