THE FORMS CARVED AND MOLDED BY WAVES 241 



The continuation of the visible in the usually invisible bar, is 

 at the time of high winds made strikingly apparent, for the wave 

 base is below the crest of the bar, and at such times its crescentic 

 course beyond the spit can be followed by the eye in a white arc 

 of broken water. 



The construction of a barrier across the entrance to a bay trans- 

 forms the latter into a separate body of water, a lagoon, within 

 which silting up and peat 

 formation usually lead to an 

 early extinction (p. 429) . The 

 formation of barriers thus 

 tends to straighten out the 

 irregularities of coast lines, 

 and opens the way to a 

 natural enlargement of the 

 land areas. While the coasts 

 of the United Kingdom of 

 Great Britain have been 



losing Some four thousand FlG . 2 64. Barrier beach in front of alagoon 

 acres through Wave erosion, on Lake Mendota at Madison, Wisconsin. 



there has been a gain by The shallow la g on behind the barrier is 



., . . . , , . , filling up and is largely hidden in vege- 



growth in quiet lagoons which t ation. 



amounts to nearly seven 



times that amount. As evidence of the straightening of the shore 



line which results from this process, the coast of the Carolinas or 



of Nantucket (Fig. 459) may serve for illustration. 



The land-tied island. We have seen that wave erosion oper- 

 ates to separate small islands from the headlands, but the shore 

 currents counteract this loss to the continents by throwing out 

 barriers which join many separated islands to the mainland. Such 

 land-tied islands are a common feature on many rocky coasts, 

 and upon the New England coast they usually have been given the 

 name of " neck." The long arc of Lynn Beach joins the former 

 island of Nahant, through its smaller neighbor Little Nahant, 

 to the coast of Massachusetts. A similar land-tied island is 

 Marblehead Neck. The Rock of Gibraltar, formerly an island, 

 is now joined to Spain by the low beach known as the " neutral 

 ground." The Spanish name, tombola, has sometimes been em- 

 ployed to describe an island thus connected to the shore. 



