Whitaker — On Subaerial Denudation. 491 



rivers often run along the foot of Chalk and Tertiary escarpments, 

 whilst, on the other hand, it is very rare for the sea to do so. 



Again, an escarpment is remarkable for the comparatively uniform 

 level of its top for long distances, any change therein being by a 

 gentle slope ; whilst the height of a range of cliffs is ever varying, 

 and that suddenly and with sharp slopes. Escarpments, too, are 

 nearly always the highest part of a district, the ground falling from 

 them on both sides ; cliffs, however, are very rarely so, but are often 

 backed by higher ground ; indeed those cases that I know of Chalk 

 cliffs being through the highest groimd are just where they cut 

 through the escarpment, as on the north of Folkestone and at Beachy 

 Head. The same kind of reasoning that has been used with refer- 

 ence to the features of the Chalk and the Tertiary beds may be 

 applied to other formations ; and how, therefore, an escarpment can 

 be an old sea-cliff passes my understanding, for the two have nothing 

 in common and much in opposition, as may be clearly seen from the 

 following table : — 



COMPARATrVE TaBLE OP THE DISTINCTIVE FEATURES OF ESCARPMENTS AND ClEFFS. 



Escarpments. Cuffs. 



{a) Eun along the strike, or in other {a) Earely run along the strike, but at 



words, keep to one formation throughout. all angles to it, and cut through many 



formations in succession. 



{b) Tops more or less even and nearly {b) Tops mostly very uneven, 



flat. (e) Earely through the highest ground 



(c) Form the highest ground of a of a country, but mostly backed by higher 

 country, overlooking other parts. ground. 



(d) Very rarely have the sea at their {d) Sea at their foot, 

 foot, but often springs and watercom'ses. 



{e) Often run in more or less winding {e) Eun nearly straight, or in curves of 



Knes. very large radius, when through homo- 

 geneous rock, and when not broken 

 through by valleys. 



ffj No beach at their foot. ffj Mostly a beach at their foot. 



{g) Are now being destroyed by the sea {g) Are now being made by the sea 



in places where the sea touches them. (aided by atmospheric actions). 



(A) Bases rise towards the watershed (li) Bases at the sea-level, 

 and have nothing to do with the sea-level. 



(e) Those of successive formations run (») No such parallel arrangement 

 in more or less parallel lines for long dis- known, long fringes of land divided by 

 tances, with plains, vales, or valleys be- belts of sea not being common, except in 

 tween. such cases as Coral Islands, where the 



features have been caused by growth, not 

 by decay. 



What can be more different than these two ? It is for those who 

 say that escarpments are old sea- cliffs to answer the question, and 

 until that has been done they have little reason on their side. 



8. — Conclusion. 



All geologists know that rivers have made great deposits, as for 

 instance the Wealden Beds, and therefore I do not see how they can 

 avoid allowing that rivers, etc., have been the agents in effecting a 

 great amount of denudation. The solid matter of the Wealden Beds 

 must have existed somewhere before, and must have been worn away 

 by subaerial actions and carried off by streams (the sea being quite 



