316 E. M. KINDLE RECONNAISSANCE OF PORCUPINE VALLEY 



portion of the river hard rocks nowhere outcrop. The banks rise gener- 

 ally 12 to 18 feet above low water and never more than a few feet above 

 high water. Entirely without topographic relief, this extensive region 

 is covered with niuskeag, spruce forest, and willows. The latter occupy 

 the intermediate border between the swampy muskeag and the better 

 drained spruce forest tracts, as well as the areas subject to river overflow. 

 Numerous sloughs or side channels diverge from the river, often keeping 

 independent courses for many miles before they rejoin the main stream. 

 These increase in number and complexity toward the mouth of the 

 stream, where it splits up into a number of separate channels, which join 

 the Yukon along the western margin of a maze of islands. Three streams 

 of considerable volume join the Porcupine in this flat. These are the 

 Big and Little Black rivers, from the southeast, and the Salmon river, 

 from the north. Each of these streams, like the Porcupine, has its source 

 in a mountain region, but traverses a wide tract of the Yukon flats before 

 joining the Porcupine. Prospectors report that the first hills and bed- 

 rock are encountered on the Salmon river "60 or 80 miles" from the 

 Porcupine. Notn'ithstanding the extreme flatness of the plain traversed 

 l^y the Porcupine, it has a very decided tilt toward the west, as shown by 

 the strong current, averaging 4 or 5 miles an hour. 



The elevated area lying to the east of the Yukon flats includes two 

 distinct mountain belts, both trending north and south. The more west- 

 erly of these mountain belts lies immediately east of the Yukon flats and 

 comprises a range of low mountains and hills. These have gentle slopes 

 and are sparsely wooded nearly to their summits. Their maximum ele- 

 vation probably does not exceed 3,000 feet. They approach the river as 

 low hills. This western hill and mountain belt appears to be coextensive 

 in width with the Lower Eamparts, a term used to designate the low, 

 nearly continuous limestone cliffs which form the channel of the river 

 for about 25 miles above the Yukon flats. A few outlying hills break up 

 the eastern edge of the Yukon flats, but they are distinctly lower than 

 the main range of the Lower Eampart hills. This is doubtless due in 

 part to the fact that the former are composed mainly of shales and the 

 latter of limestone. 



The second mountain belt lies near the International boundary. It 

 appears to show somewhat stronger relief than the belt just described, but 

 the maximum elevation attained near the river probably does not exceed 

 3,500 feet. The highest point seen within 6 or 7 miles of the river on 

 the north rises 1,640 feet above the Porcupine. This eastern mountain 

 and hill belt appears to be confined to a zone of rocks in which quartzites 

 predominate. These quartzites doubtless in part determine its position. 



