Chap. X.] THE LAPSE OF TIME. 58 



ductions, showing how little they are abraded and how 

 seldom they are rolled about ! Moreover, if we follow 

 for a few miles 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, wliich 

 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, wliich 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 

 intersection of various formations. This being the case, 

 we are compelled to admit that the escarpments owe 



