Chap. IX. GEOLOGICAL EECOED. 283 



process of degradation. The tides in most cases reach 

 the cliffs only for a short time twice a day, and the 

 waves eat into them only when they are charged 

 with sand or pebbles ; for there is reason to believe 

 that pure water can effect little or nothing in wearing 

 away rock. At last the base of the cliff is under- 

 mined, huge fragments fall down, and these remain- 

 ing fixed, have to be worn away, atom by atom, until 

 reduced in size they can be rolled about by the waves, 

 and then are more quickly ground into pebbles, sand, 

 or mud. But how often do we see along the bases of 

 retreating cliffs rounded boulders, all thickly clothed 

 by marine productions, showing how little they are 

 abraded and how seldom they are rolled about ! More- 

 over, if we follow for a few miles any line of rocky cliff, 

 which is undergoing degradation, we find that it is only 

 here and there, along a short length or round a pro- 

 montory, that the cliffs are at the present time suffering. 

 The appearance of the surface and the vegetation show 

 that elsewhere years have elapsed since the waters 

 washed their base. 



He who most closely studies the action of the sea on 

 our shores, will, I believe, be most deeply impressed 

 with the slowness with which rocky coasts are worn 

 away. The observations on this head by Hugh Miller, 

 and by that excellent observer Mr. Smith of Jordan 

 Hill, are most impressive. With the mind thus im- 

 pressed, let any one examine beds of conglomerate 

 many thousand feet in thickness, which, though pro- 

 bably formed at a quicker rate than many other depo- 

 sits, yet, from being formed of worn and rounded 

 pebbles, each of which bears the stamp of time, are 

 good to show how slowly the mass has been accumu- 

 lated. Let him remember Lyell's profound remark, 

 that the thickness and extent of sedimentary formations 



