“ The "Yukon Flats" flank the river for about 200 m. and are from 40 to 100 m. wide. Here the stream varies in width from 10 to nearly 20 m., and involves a confused network of constantly changing channels. Here, too, the river makes its great bend to the S.W., and its channels are constantly changing. The "Flats" are monotonous areas of sand bars and low islands, thickly wooded with spruce. The principal tributaries here are the Porcupine river (an important affluent, which enters the main stream at the great bend about 3 m. N. of the Arctic Circle) ”

“ At the W. edge of the Ramparts the Yukon receives the Tanana river, its longest tributary lying wholly within Alaska. The Tanana Valley is about 400 m. long, nearly parallel to the Yukon from about due W. of its headwaters to the great bend, and drains about 25,000 sq. m. Its sources are chiefly glaciers in the Alaskan Range and it receives many tributaries. The Yukon delta begins near 63° N. Here the main stream branches into several channels which follow N. or N.W. courses to Norton Sound. The northernmost of these channels is the Apoon Pass, and the most southerly is Kwikluak Pass ”