Plains of Marine Demidation. 497 



Association at Oxford in 1847. The dark-coloured 

 part represents the form of the country given Fig. 97. 

 in the original sections on a scale of six inches ^ J x 



to a mile horizontally and vertically. The 

 strata of this area, and, indeed, of much of 

 South Wales, are exceedingly contorted. The 

 level of the sea is represented by the lower line ; 

 and if we take a straight-edge, and place it on 

 the topmost part of the highest hill, and incline 

 it gently seaward, it touches the top of each 

 hill in succession, in the manner shown by the 

 line 6 b. This line is as near as can be straight, 

 and, on the average, has an inclination of 

 from one to one and a half degrees; and it 

 is a curious circumstance that in the original p 

 line of sections there were no peaks rising 

 above that line they barely touched it and no 

 more. It occurred to me when I first observed 

 this circumstance that, at a period of geologi- 

 cal history of unknown date, perhaps older than 

 the beginning of the deposition of the Permian 

 and New Eed Sandstones, this inclined line that 

 touches the hill-tops must have represented a 

 great plain of marine denudation. 



Atmospheric degradation, aided by sea 

 waves on the cliffs by the shore, are the only 

 powers I know that can denude a country so as 

 to shave it across, and make a plane surface 

 either horizontal or slightly inclined. If a 

 country be sinking very gradually, and the rate 

 of waste by all causes be proportionate to the 

 rate of sinking, this will greatly assist in the 

 production of the phenomena we are now 

 considering : and a little reflection will show, 



K K 



