152 PHYSIOGRAPHY 



movements will be studied in a later chapter, but it may be stated 

 here that if an area sinks, as has sometimes happened, it may give 



Fig. 153. Section across the mountains of Palestine, to the mountains of 

 Moab, showing the position and relations of the Dead Sea. 



rise to a depression fit for a lake (Fig. 153). The sinking may come 

 about in various ways, as we shall see. 



The Topographic Features of Shores 



Reference has been already made to certain topographic features 

 of lake shores, but the topic is of so much importance that it must 

 be studied a little more in detail. 



Waves, currents, rivers, winds, glaciers, ice formed along the 

 shore, and various other agencies are working on the shores of seas 

 and lakes, and each has some effect on the coast line. Of these, the 

 waves, and the movements of the water to which the waves give 

 rise, are the most important. 



1. Waves, undertow, shore currents. Waves are cutting in on 

 some parts of the shore of almost every lake, and they are more 

 active when the wind blows than at other times. Away from the 

 shore, the water in a wave does not move forward. Some idea of 

 its motion may be gained from a field of waving grain, where each 

 moving stem is fixed to the ground, though wave after wave crosses 

 the field. Some conception of the motion may also be gained if 

 one end of a long piece of rope is fixed, while the other is shaken 

 up and down. Successive waves travel from the end shaken to the 



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Fig. 154. Diagram to illustrate the movement of water in waves. The 

 small circles represent the movement of water particles. 



end which is fixed. In these illustrations the grain and the rope 

 come to rest just where they started. Fig. 154 gives some idea of 

 the nature of the movement of water in a wave where the water is 



