280 Proceedings of the Royal Physical Society. 



gravel-covered bear a direct relation to the travelling of the 

 stream curves. Streams themselves occupying only a narrow 

 waterway, all parts of their courses not kept open by the 

 scour of the current are silted up with deposits of the stones, 

 sand, and mud, which the stream has in train. Thus it 

 comes about that the movements of curves are exactly kept 

 pace with by the growth of alluvial deposits. The concavi- 

 ties of the river-bends are scooped out by erosion ; the con- 

 vexities that fit into them on the opposite side are thrust for- 

 ward by deposition ; and the windings of streams will gener- 

 ally exhibit on any one side alternate deflection-pools and 

 gravel banks (Figs. 7 and 13).* 



Fig. 9. 



Sketch Section across a stream-curve, showing the formntion of 

 River Gravel by accretion. 



Gra., Sd., B. CI. = Gravel, Sand, and Boulder Clay. 



In the transverse section of a deflection-pool we find that 

 it usually shallows out from the deepest or deflecting side. 

 At the base of the scar we can often see something of the 

 raw material, whether rock or boulder clay, on which the 

 river is at work. The stones in the stream-bed on that side 

 — some of them freshly detached, others dropped from the 

 grasp of the last flood when it began to slacken, and could 

 drag them down stream no longer — are few and large, and, 

 lying in the thread of the stream, are bearing the full force 

 of the current. Crossing the stream from the deflecting bank, 

 the bottom shelves up, the water loses its motion, the average 

 size of stone underfoot becomes smaller and smaller, and the 

 gravel may pass into shingle, pebbles, and pebblets, by a 

 gradation evidently due to mechanical assortment connected 



* III these figures the position of several gravel-banks is marked by stippling. 

 The position of the deflection-pools may be inferred. 



