676 DYNAMICAL GEOLOGY. 



and granite, on the Connecticut coast, illustrate well this action, and 

 by the kind of rock as well as the results, show how destruction went 

 forward when, as in Archaean time, the ocean had to work without the 

 help of rivers. Cliffs are often made of horizontal beds, and then the 

 rocks, when the beach is not wide enough to serve as a breakwater, 

 are quickly undermined. 



But simple impact is aided by abrasion, carried forward by the 

 stones and gravel which the hurrying wave takes up and throws at 

 the cliff. The dash forward and the flow backward, carry on the mu- 

 tual abrasion of the sands, gravel, stones, and rocks of the shores, re- 

 ducing the coarser to sand, besides grinding the sands to a finer pow- 

 der. In view of the force at work it is not surprising that, in regions 

 like Cape Horn, or the coast of Scotland, where storms are common, 

 the cliffs should undergo constant degradation, and be fronted by lofty 

 castellated and needle-shaped rocks, or that the land should yield be- 

 fore the encroaching sea. The long leathery seaweed of coasts, in 

 some seas scores of yards in length, are a great protection to the 

 rocks. 



The cliffs of Norfolk and Suffolk, England afford an example that has been long 

 under observation, as the country is one of houses and cultivated fields. Lyell states 

 that in 1805, when an inn at Sherringham was built, it was fifty } r ards from the sea, 

 and it was computed that it would require seventy years for the sea to reach the 

 spot — the mean loss of land having been calculated, from former experience, to be 

 somewhat less than one yard annually. But it was not considered that the slope of 

 the ground was from the sea. Between the years 1824 and 1829, seventeen yards were 

 swept away, bringing the waters to the foot of the garden ; and in 1829 there was 

 depth enough for a frigate (twenty feet), at a spot where a cliff of fifty feet stood forty- 

 eight years before. Farther to the south, the ancient villages of Shipden, Wimpwell, 

 and Eccles have disappeared. This encroachment of the sea has been going on from 

 time immemorial. Many examples might be cited from the American coast; but none 

 so remarkable have yet been described. 



3. The wearing action of waves on a coast is mainly confined to a 

 height between high and low tides. — Since a wave is a body of water 

 rising above the general surface, and when thus elevated makes its 

 plunge on the shore, it follows that the upper line of wearing action 

 may be considerably above high-tide level. 



Again, the lower limit of erosion is above low-tide level ; for the 

 waves have their least force at low tide, and their greatest during the « 

 progressing flood ; and, when the waves are in full force, the rocks be- 

 low are already protected by the waters, up to a level above low-tide 

 mark. There is, therefore, a level of greatest wear, which is a little 

 above half tide, and another of no wear, which is just above low tide. 



This feature of wave action, and the reality of a line of no wear, 

 above the level of low tide, are well illustrated by facts on the coasts 

 of Australia and New Zealand. In Figure 1096 (representing in pro- 



