LAND WATERS STREAMS 187 



one time and fine at another. Flood-plain deposits are often, 

 therefore, very heterogeneous, ranging from the finest mud, through 

 sand, to gravel, and even bowlders. In general they become finer 

 down-stream. In a given plain, they are usually coarser at the 

 bottom, and finer toward the top. 



Flood-plain meanders. A stream with an alluvial plain is 

 likely to meander widely (Pis. XIV and VIII). In general terms 

 this may be said to be the result of low velocity, which allows the 

 stream to be turned aside easily. Were the course of such a stream 

 made straight, it would soon become crooked again. The manner 



Fig. 158. A delta in a lake. The village is Silva Plana, in the Engadine, 

 Switzerland. (Robin.) 



of change is illustrated by Figs. 154 and 155. If the banks are 

 less resistant at some points than at others, as is always the case, 

 the stream will cut in at those points. If the configuration of the 

 channel is such as to direct a current against a given point, 

 b (Fig. 154), the result is the same, even without inequality of 

 material. Once a curve in the bank is started, it is increased by 

 the current which is directed into it. Furthermore, as the current 

 issues from the curve, it impinges against the opposite bank and 

 develops a curve at that point. The water issuing from this 

 curve develops another, and so on. 



Once started, the curves or meanders tend to become more 

 and more pronounced (Fig. 155). In the case represented by 

 Fig. 1, PI, VIII, the narrow neck of land between curves is almost 



