LAND WATERS STREAMS 



185 



occasionally. 1 At Blair, about 25 miles above Omaha, the same 



river is believed to cut to bed-rock (about 40 feet below the bottom 



| of the channel in low water) during floods. 2 All streams similarly 



; situated do a like work. The material thus eroded is shifted down- 



Fig. 156. Meanders and cut-offs in the Mississippi Valley below Vicksburg. 

 The figure shows the migration of the meanders down stream, and their 

 tendency to increase. 



stream, some of it for short distances only, and some of it to the 

 sea. Even an aggrading stream therefore is not without erosive 

 activity; it is a stream whose fill exceeds its scour, not one which 

 has ceased to erode. 



Materials of the flood-plain. As a result of its varying velocities 

 in flood and low water, a stream may deposit coarse material at 



'Cooley. Kept. U. S. Engineers for 1879-80, Pt. II, pp. 1060 and 1071. 



2 Gerber. Cited by Todd. Bull. 158, U. S. Geol. Surv., pp. 150, 151. 



