Athabaska river, which is the most southerly of the three great tributaries of the Mackenzie, rises in Rocky mountains near Mount Brown, at an altitude of about five thousand seven hundred feet, and pursues a northeasterly and northerly course for nearly six hundred miles to Athabaska lake, falling in this distance some five thousand feet, and being interrupted by several series of rapids. In the first three hundred miles of its course it falls about four thousand feet, and receives in succession Baptiste river from the west, the Macleod and Pembina from the south, and the Lesser Slave, draining the large lake of that name, from the west. Below its confluence with the last named stream, the Athabaska turns southeastward for some fifty miles and then resumes its northerly course. In the course of the next one hundred and fifty miles it receives, in succession, La Biche river from the east; Quito or Calling river from the west; Big Mouth brook from the east; Pelican river from the west; and House river from the east. Just below the mouth of the last river the Athabaska strikes a range of low hills, and in forcing a passage through them is deflected eastward, and for a distance of about seventy-five miles contains many rapids, falling in this distance some four hundred feet. At the lower end of this stretch it receives the waters of Clearwater river, its principal tributary below Lesser Slave river. The Clearwater rises on the height of land between the Churchill and the Athabaska, and pursuing a nearly straight easterly course for some one hundred and fifty miles, mingles its limpid waters with the sediment-laden flood of the latter stream. In the lower part of its course the Clearwater occupies a deep valley and is very rapid. Thirty or forty miles above its mouth it is joined by the Pembina, a stream of about equal volume. Below the mouth of the Clearwater the Athabaska pursues a nearly direct course northward, receiving Red, Moose, and Bar rivers from the west, and enters Athabaska lake through a number of channels including alluvial islands. Lake Athabaska was known to the pioneer fur-traders and explorers as “Lake of the Hills,” and it is so described by Mackenzie and others. The country drained by the Athabaska is MAINLY A ROLLING PLAIN and with the exception of a few areas of semi-prairie land, is well wooded, with a forest composed mainly of spruce, fir, pine, tamarack, poplar, birch and willow. A large part of its surface is occupied by mossy swamps, called muskegs, and hundreds of ponds and lakes, of which Lesser Slave, seventy miles in length, is by far the largest, occupy its shallow valleys. Immense areas have been swept by fire, sometimes repeatedly, and in some places the original forest covering has been destroyed and small prairies have succeeded.