302 FIRST YEAR SCIENCE 



The main characteristics of a coast which has been ele- 

 vated, that is, of one in which the shore line has moved sea- 

 ward, will readily suggest themselves to any one who 

 considers what has taken place. Soundings show that the 

 continental shelf has a comparatively smooth surface. 

 Thus the water will meet the land in an almost straight 

 line and the deepening of the water off shore will be grad- 

 ual. The material forming the shore both below and 

 above the water line will be easily eroded, since it has 

 been recently deposited and has not had time to consolidate. 



SAND DUNES FORMED UPON A SAND BAR. 



Waves rolling in upon the shore will strike the bot- 

 tom at a considerable distance off shore. Thus the water 

 rapidly loses its velocity and its power to carry eroded 

 material shoreward, so it builds at a distance from the 

 shore a sand reef inclosing a lagoon. The currents caused 

 by the prevailing winds and the tide flowing along the out- 

 side of this barrier give it for long distances a smootfr 

 outline, sometimes almost straight and sometimes gently 

 curving. Dunes are formed upon these bars. In time 



