xix. NATURAL ESCARPMENTS. 485 



re-elevated to -S 1 ' 1 , sunk again to $ iv , and finally restored to its 

 original level at S*. E would represent an eocene basin, G a glacial 

 basin, separated in point of time by P, pre-glacial, if not also 

 pleiocene and meiocene land. S v is our present condition one, as 

 it appears, of elevation, which perhaps in a space of time sufficiently 

 long may be exchanged for depression. 



These remarkable and extensive oscillations, by upward and 

 downward movements of the land within certain limits, and several 

 times repeated, are difficult to explain by any theory concerning the 

 condition of the earth's interior masses. One might frame another 

 explanation, by supposing a limited sea at a different level from 

 the main ocean, and subject to variation of level by change of 

 boundary and other causes; but this helps us little, for the pro- 

 duction of such a variable sea implies earth movements not less 

 difficult of explanation than the others, and more complicated in 

 operation. 



We are not, however, now concerned with theoretical explana- 

 tions of the movements ; such investigations cannot be conducted 

 on so narrow a basis as even the islands of Britain, much less on 

 the basin of a single river. Let us therefore turn to trace the 

 effects of these movements, which must be admitted as real and 

 effective in altering the surface of the country under review. 



Diagram CCIX. Waste of the Earth's Surface. 



Let A, B, C, D, E, F, G, H be a mass of stratified matter, partly 

 firm and coherent rock, as h, and partly softer matter, as clay ; 

 the whole raised above the sea, so as to have a uniform inclination 

 from D H to A E. It will be found as a general rule that hollows 

 formed in the clays run between escarpments formed of the rocks. 

 In the oolitic districts the slope to the right below H is on lias 

 clay; that below G is on Oxford clay; that below F is on Kim- 

 meridge clay. These hollows and escarpments extend for twenty, 

 forty, or more miles, and the explanation which seems most 



