The province here to be considered embraces that part of the Alaska-Yukon basin lying adjacent to the International boundary (141st meridian) and stretching westward to the 152d meridian. The Tanana river can be regarded as its southern boundary, and it extends northward to about the 67th parallel of latitude. Most of the observations on which the present paper is based were made in the eastern half of this area.
This region is drained by the Yukon river and its tributaries, the largest being the Porcupine river, joining the Yukon from the northeast at its great bend near the Arctic circle, and the Tanana, flowing westerly, which joins the Yukon about 200 miles to the southwest of the mouth of the Porcupine (see map, figure 1). The region forms a part of the so-called Plateau region of central Alaska, being the intermontane belt bounded on the south by the ranges . . .