156 THE OCEAX. 



in width, and perhaps ma}' then be compared to a narrow cornice, 

 suspended at mid-way between two abrupt walls, that of tlie 

 cliff, and that which plunges into the abyss of the water. On 

 the other hand, when the rocks are easily cut, the terrace of one or 

 several stages over which the waves roll, has sometimes many hun- 

 dreds of yards in width. At Inishmore, on the western coast of 

 Ireland, the cliff presents a succession of regular steps like those of 

 a staircase cut out for giants. The highest step, all encumbered with 

 blocks, is that attained by the waves during a tempest; lower down 

 are those bathed by the spring- tides, and then that where the ordinary 

 tides are arrested. Still lower are the intermediary terraces, and 

 the last two steps of the staircase are those where the water breaks 

 during ordinary ebb, and at the low tides of the equinoxes.* 



-1 f 



Fie. 63.— Tides of Inishmore. (Kinahan.) 



a. Deposit of tomposts. b. Terrare of equinoctial tides. c. Terrace of ordinary high tides. 



dd. Intenucdiary terraces. e. Terrace of ordinary low tides. /. Low equinoctial tides. 



It will be easily understood that these submarine ledges were for- 

 merly embedded in the thickness of the rock ; they have resisted 

 the assault of the waves, while the higher strata, sapped at their 

 base more or less slowly, have fallen into the water. As the force 

 of the waves is felt much less in the mass of waters than on the surface 

 of the sea, the rock only allows itself to be cut into at the place where 

 the breakers dash. But its submerged slopes remain relatively intact, 

 and maintain more or less exactly the ancient outline of the coast. 

 This is the reason why there exists on the shores of the Atlantic, and 

 other seas, the level of which oscillates alternately with the ebb and 

 flow, two platforms, one above the other, which correspond, the one 

 with the level of low water, the other with that of high water. At 

 the time of flow, the waves, urged by the tides, and more often too 

 by the wind which accompanies the tide,t dash impetuously against 

 the rocky walls, and push on vigorously their labours of destruc- 



♦ Kinahan, Geological Magazine, August, 1866. 

 t See below, the section entitled. The Air and the Winds. 



