Dr. C. Callaway — On River Curves. 453 



above the convexity, but in some part of it. Fig. 2 will illustrate 

 this point. The aflSuent CD enters the river AB above the convexity. 

 But the delta-like mass of laud E has grown up-stream, and the 

 broken lines represent the new course of the river, with the affluent 

 entering it at D'. 



B 



B' ~ ^ ^ 



Fig. 2.— Growth up-stream of delta (E) formed by affluent C D, subsequently C D'. 



The principles I have expounded are quite consistent with the 

 occasional entrance of a tributary on the concavity of a curve. This 

 may occur in several ways. 



1. An affluent may originally have entered the river on the 

 convex. Then a change may take place in the main stream by 

 increase or decrease of slope or volume, so that a new set of 

 curvatures may be produced, the causes in operation being powerful 

 enough to overpower the effect of the affluent. Thus a concavity 

 may take the place of a convexity. 



2. An affluent may enter on the concave owing to its excessively 

 swift motion. This appears to be the case in the valley of the 

 Khone near Sion. According to Lord Avebury,^ the Borgne falls 

 into the Ehone at this place with such velocity as to drive it to the 

 opposite side of the valley, the affluent entering the Ehone on the 

 concave across an alluvial flat. It would seem that the entry of 

 the tributary was originally so swift that it struck the further bank 

 and rebounded, so as to deposit its sediment on its own side. The 

 growth of this delta would gradually force the Ehone to the opposite 

 side of the valley. 



3. Two affluents may enter a river opposite to each other. The 

 one that entered with the greater velocity (up to a certain point) 

 would be likely to come in on the convex, for it would have greater 

 power to convey its sediment to the opposite bank, and thus to draw 

 the river to its own side. The smaller tributary would of course 

 come in on the concavity. 



4. The entry of an affluent on the concave may be due to 

 the deposit of sediment at the junction of the two streams. An 

 interesting example of this occurs on the Severn, about 6 miles 

 south-east of Shrewsbury. It is shown in Fig. 3. Cound Brook 

 enters on the concave at A. The last mile of the course of 

 the brook is through an alluvial flat. Now it appears highly 

 probable that at one time the river curved round into this bay, 

 as suggested by the broken lines ; otherwise its excavation is not 



1 " Scenery of England," p. 319, fig. 133. 



