The Coast-line 



large steps, and that the uppermost of these consisted 

 of larger boulders than those which constituted the 

 lower ones. This was the storm beach, and was only 

 reached by the water at high tide during storms, when 

 the waves were sufficiently powerful to move the large 

 heavy masses. The lower steps, consisting as they did 

 of smaller, lighter pebbles, were the product of the 

 smaller waves of fine weather, and their arrangement in 

 successive terraces was due to the varying height of the 

 tides. In this particular instance there were two beaches 

 below the storm beach, and these we may call the 

 spring-tide and neap-tide beach respectively. 



When a breaking wave has driven the stones up the 

 slope of the beach, the undertow produced by the re- 

 treating water carries some of them back again, but as 

 the force of the on-rushing wave is much greater than 

 that of the undertow, the latter is only able to carry 

 back the smaller pebbles and sand, and that is why the 

 shingle always accumulates near high-water mark 

 instead of being distributed all over the shore. 



On examination of the materials of the shingle, we 

 found that it consisted for the most part of rounded 

 masses of a heavy dark-gray rock which is called basalt, 

 but there were also some pieces of a white material 

 which could be easily scratched with a knife, and which 

 proved on further examination to be limestone ; also 

 numerous pebbles of flint. 



These boulders must have been broken away from 

 the cliffs by the waves, and, scrambling over the shingle, 

 we examined the cliffs behind. These we found to 

 vary in height from 10 to 30 feet, and to consist of 

 horizontal beds of brownish clay with three thin layers 



77 



