CiiAP. IX. THE LAl'SK OF T1MI<:. 2G9 



sciliincntiiry formations arc the result and the measure of the 

 rlrnudation which the eartli's crust lias elsewhere under<roue. 

 Therefore a man should examine for himself the great piles of 

 superimposed strata, and watch the rivulets brini^ini^ down 

 niuil, and the waves wearing away the sca-clills, in order to 

 comprehend something about the duration of past time, the 

 monuments of which we sec all around us. 



It is good to wander along the coast, when formed of raod- 

 eratcly-hard rocks, and mark the process of degradation. The 

 tides in most cases reach the cliffs only for a short time twice a 

 day, and the waves cat into them, only when they are charged 

 with sand or pel)bles ; for there is good evidence that pure 

 water elfects nothing in wearing away rock. At last the base 

 of the cliff is undermined, huge fragments fall down, and these, 

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

 after being reduced iii size they can be rolled about by the 

 waves, and then they are more quickly ground into pebbles, 

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

 retreating cliffs rounded bowlders, all thickly clothed by marine; 

 productions, showing how little they are abraded, and how 

 seldom they are rolled about ! Moreover, if we follow for a 

 few miles any line (jf rocky cliff, which is undergoing degrada- 

 tion, we find that it is only here and there, along a sliort length 

 or round a promontory, that the clifl's arc at the present time 

 suffering. The appearance of the surface and the vegetation, 

 show that elsewhere yeai'S have elapsed since the Avaters 

 washed their base. 



We have, however, recently learned from the observations 

 of Ramsay, in the van of" excellent observers, of Jukes, Geikie, 

 Croll, and others, that subaerial degradation is a much more 

 imi)ortant agency than coast-action, or the power of the waves. 

 Tiie whole surface of the land is exposed to the chemical ac- 

 tion of the air and of the rain-water with its dissolved carbonic 

 acid, and in colder countries to frost; the disintegrated matter 

 is carried down even gentle slopes during heavy rain, and to a 

 greater extent than might be supposed, especially in arid dis- 

 tricts, by the wind ; it is then transported by the streams and 

 rivers, which when rapid deepen their chainicls, and triturate 

 the fragments. On a rainy day, even in a gently-undulating 

 country, we see the effects of subaerial degradation in the mud- 

 dy rills Avhich flow down each slope. Messrs. Kamsay and 

 Whitaker have shown, and the observation is a most striking 

 one, that the great lines of escarpment in the Wcaldon district 



