IMPERFECTION OF GEOLOGICAL RECORD 59 



we find that it is only here and there, along a short 

 length or round a promontory, 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. 



We have, however, recently learned from the observa- 

 tions of Eamsay, in the van of many excellent observers 

 — of Jukes, Geikie, CroU, and others — that subaerial deg- 

 radation is a much more important agency than coast- 

 action, or the power of the waves. The whole surface 

 of the land is exposed to the chemical action 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, espe- 

 cially in arid districts, by the wind; it is then trans- 

 ported by the streams and rivers, which when rapid 

 deepen their channels, and triturate the fragments. On 

 a rainy day, even in a gently undulating country, we 

 see the effects of subaerial degradation in the muddy 

 rills which flow down every slope. Messrs. Earnsay and 

 Whitaker have shown, and the observation is a most 

 striking one, that the great lines of escarpment in the 

 Wealden district and those ranging across England, which 

 formerly were looked at as ancient sea-coasts, cannot have 

 been thus formed, for each line is composed of one and 

 the same formation, while our sea-cliffs are everywhere 

 formed by the intersection of various formations. This 

 being the case, we are compelled to admit that the es- 

 carpments owe their origin in chief part to the rocks 

 of which they are composed having resisted subaerial 

 denudation better than the surrounding surface; this sur- 



