436 HENRY M. EAKIN 



section profiles of the stream would be correspondingly modified, 

 and a difference in lateral erosion would ensue. The efficiency of 

 rotation to produce appreciable results is advocated only in "con- 

 nection with and as an adjunct to lateral wear by means of curvature." 



In certain Alaska streams the writer has noted a strong predomi- 

 nance of erosion on the right bank, shown by asymmetry in the 

 position of the river with respect to the flood plain, the distribution 

 of bluffs on the right and left limits, and in the distribution of bars and 

 islands relative to cut banks. In the case of the Yukon, in the last 

 600 miles of its course the flood plain, 20 to 50 miles wide, is almost 

 entirely on the left-hand side. It flows close to the right valley 

 wall almost the entire distance, often with steep, fresh-cut bluffs 

 in bed-rock. The left bank is commonly alluvium, bed-rock being 

 encountered only once in this distance. And in the single instance 

 mentioned, opposite the mouth of the Melozi River, a large delta 

 has been built out by the tributary stream, literally crowding the 

 larger river over to the left valley wall. In this part the Yukon is 

 essentially without meanders, being characterized by long straight 

 reaches and gentle curves. 



Also of great significance in the case of the Yukon is the behavior 

 of driftwood and floating debris. Such material is almost entirely 

 absent from the left bank, but is plentiful on the right. And in 

 flood time, when the current is well supplied with such material, its 

 distribution on the stream surface is most striking. It is confined 

 almost entirely to the right half, and often to a much smaller space 

 along the right bank. Eddies along the right limit are often crowded 

 with drift; along the left never, so far as observed. At Nulato, 

 where the river is about a mile wide, the natives get a large supply 

 of wood by catching drift logs, and they seldom have to go more than 

 300 feet from the right bank to secure them. 



The problems presented by these conditions have stimulated study, 

 which has led to an analysis of the processes of river erosion consider- 

 ably different from that described above. In the following pages, 

 after a simple review of the principles to which the deflective force 

 is due, it is intended to emphasize its greater strength in higher lati- 

 tudes, to show that its expression in unbalanced lateral erosion is 

 least in streams where meanders are in process of development and 



