WAVE-EROSION 179 



same region. On the coast of England the sites of villages have 

 disappeared by the advance of the sea within historic times, 1 but 

 the coast of the same island affords illustrations of land advance. 

 On the south side of Nantucket Island, the sea-cliff has been known 

 to retreat before the waves six feet in a single year. 2 Almost every 

 considerable stretch of coast affords illustrations both of the advance 

 of sea on land and of land on sea; but in the long run, the former 

 exceeds the latter. 



Topographic features developed by wave-erosion. As the 

 waves cut into the shore at and near the water-level, they develop 

 a steep slope above the line of cutting. This steep slope is the sea- 

 el I jj (Fiijs. 181 to 184). The term lake cliff is applied to the cor- 

 responding cliffs of lakes. 



The height of the cliff depends on the height of the land along 

 shore. Its slope may be steep or gentle (Figs. 181 and 182). Rapid 



183. A high sea clitl without ;i beach, La Jolla, Cal. 



cutting and resistant material tend to produce steep cliffs; but 

 steep cliffs may develop in incoherent materials, such as sand and 

 clay, if cutting is rapid. The structure of the cliff-rock also in- 

 fluences the slope and configuration of the sea-cliff. By working 

 in along the joints of the rock, widening them and quarrying out 

 the intervening blocks, pillars of rock ("chimney-rocks" " pnlf>it- 



, Manual of Geology, 4th ed., p. 219. 

 2 Shaler, Sea and Land, p. 29. 



