Chap. X.] THE LAPSE OF TIME. 53 



ductions, showing how little they are abraded and how 

 seldom they are rolled about ! Moreover, if we follow 

 for a few rniles any line of rocky cliff, which is under- 

 going degradation, 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 learnt from the obser- 

 vations of Eamsay, in the van of many excellent 

 observers — of Jukes, Geikie, Croll, and others, that 

 subaerial degradation 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, especially in arid districts, by the wind ; it 

 is then transported by the streams and rivers, which 

 when rapid deepen their channels, and triturate the 

 fragments. On a rainy day, even in a gently undula- 

 ting country, we see the effects of subaerial degradation 

 in the muddy rills which flow down every slope. 

 Messrs. Eamsay 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, 

 whilst our sea-cliffs are everywhere formed by the 

 mtersection of various formations. This being the case, 

 we are compelled to admit that the escarpments owe 



