Chap. X.] THE LAPSE OF TIME. 53 



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 undergoing deg- 

 radation, 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 ob- 

 servers — of Jukes, Geikie, Croll, and others,, that sub- 

 aerial 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 car- 

 bonic acid, and in colder countries to frost; the disin- 

 tegrated 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 undulat- 

 ing country, we see the effects of subaerial degradation 

 in the muddy rills which flow down every slope. Messrs. 

 Ramsay and Whitaker have shown, and the observation 

 is a most striking one, that the great lines of escarp- 

 ment 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 intersection 

 of various formations. This being the case, we are 

 compelled to admit that the escarpments owe their 



