Mr. W. Whitakcr on Subaerial Denudation. 319 



served, and which have also yielded worm-burrows, will hereafter 

 still more largely illustrate the Laurentian fauna. After giving 

 short descriptions of new specimens from Madoc and from Long 

 Lake and Wentworth, Dr. Dawson discussed the objections of Prof. 

 King and Dr. Itowney to the view of the organic nature of Eozoon, 

 and stated that those gentlemen had failed to distinguish between 

 the organic and the crystalline forms, as was especially illustrated 

 by their regarding the veins of crysotile as identical with the tubu- 

 lated cell- wall of Eozoon. 



3. " On Subaerial Denudation, and on Cliffs and Escarpments 

 of the Chalk and the Tertiary strata." By W. "Whitaker, Esq., B.A., 

 F.G.S. 



From the fact that escarpments differ from cliffs in all their chief 

 features, the author inferred that the two could hardly result from 

 the same action, but that, whilst the latter were made by the sea, the 

 former seem to have been cut out by subaerial agents. 



The chief contrasts between the two kinds of ridges are : — 



(1) Escarpments always run along the strike. Cliffs rarely 

 do so. 



(2) The bottom of an escarpment is not at one level throughout. 

 That of a sea-cliff is. 



(3) At the foot of an escarpment one does not find a beach or 

 other trace of the action of the sea, but often such debris as would 

 be left by a slow and quiet denuding power. 



(4) Two escarpments facing the same way often run near and 

 parallel to one another for many miles. Not so with cliffs. 



(5) The ridge of an escarpment is a nearly even line, and forms 

 the highest ground of the neighbourhood. The top of a cliff is often 

 very uneven and bordered by higher ground. 



From an examination of escarpments of the Chalk and of the 

 Tertiary beds, it was shown that though at first sight they might 

 seem like old lines of cliff, yet a little study would destroy the 

 fancied likeness, and it would be found that they are quite unlike 

 cliffs in the same beds; for though, from their winding outline, these 

 ranges of hills might remind one of some irregular coast, caused by 

 rocks of different hardness wearing away at different rates, the)^ 

 have little in common with the far more even coast that is formed 

 where there is but one kind of rock. 



It was then pointed out that along the present coast the sea is 

 not the only force engaged in the work of destruction, but that it is 

 largely helped by atmospheric agents (the latter acting from above 

 downwards, to detach and hurl down masses of rock, which the 

 former, acting horizontally below, pounds down and sweeps away) ; 

 and it was inferred that the joint action of the two kinds of force 

 had a far greater effect than either alone. 



In conclusion it was argued that, as deposits of great thickness 

 (such as the Wealden beds) had been made by rivers, it must be 

 allowed that (allowing for waste) still greater masses of rock had 

 been destroyed by streams and by subaerial actions generally. The 

 denuding power of the sea, however, was by no means denied, but 



