ESCARPMENTS. 599 



along the Norfolk coast between Happisburgh and Weybourn, among the Glacial 

 Drifts, and again in Sheppey where the cliffs are formed of London Clay. Railway- 

 engineers are perhaps too familiar with some forms of landslips. 



We may now turn to the Escarpments of the Oolites and Chalk. 

 The term "escarpment" is applied to the elevated country formed 

 by the outcrop of certain strata, or to the bounding ridge of a 

 formation or bed, beyond which it does not extend, except in the 

 form of outliers. Escarpments usually follow the strike of the 

 strata, and hence keep to one formation, but their persistence is 

 modified by faults and local diversities in the elevation of the beds ; 

 they form the highest ground of an area with more or less even 

 summits ; while escarpments of successive formations run in more 

 or less parallel lines for long distances, with intervening vales. ^ 

 They are usually composed of porous rocks, such as limestone, 

 sandstone, and sand ; in fact the form of hills largely depends on 

 the character of the rock and its ' angle of repose.' 



Thus the North and South Downs are 'escarpments' of the 

 Chalk. The Cotteswold Hills are the 'escarpment' of the Oolites, 

 and they really consist of several minor escarpments, but that of 

 the Great Oolite is more prominent near Bath, and the Inferior 

 Oolite near Cheltenham. (See Figs. 43 and 44, p. 281.) The 

 Polden Hills, in Somersetshire, are the 'escarpment' of the Lower 

 Lias and Penarth Beds. (See Fig. 39, p. 250.) In the Carbon- 

 iferous rocks the scars and terraces of the Yorkshire dales may be 

 cited, some formed of limestone, others of alternations of sand- 

 stones and shales making ridges and hollows. 



The origin of Escarpments has been a fertile source of discussion, 

 and is a subject by no means easy to explain in a few sentences : 

 we have to consider the former extension of the strata, their up- 

 heaval, and then the agents that have denuded them. 



We have to regard the Chalk as formerly extending over the 

 denuded plain of Jurassic rocks to which reference has previously 

 been made, and we may conclude that the escarpments in these 

 older rocks (in the midland and southern counties at any rate), 

 were formed after the recession of the Chalk.* Moreover, the 

 Chalk escarpment, as Sir A. C. Ramsay has remarked, being more 

 easily wasted than that of the Oolites, its recession eastwards has 

 been more rapid. 



The denudation of the Chalk over the area of what is now the 

 Severn valley may have been commenced in Eocene times, by rain, 

 rivers, and even by estuarine agency, although we have no evidence 

 to infer purely marine action ; but it is possible that on the original 

 upheaval of the Chalk tracts, covered as they were to some extent 

 by Tertiary beds, the waters draining off the land may have marked 

 out channels that were afterwards occupied by rivers. Moreover, 

 the uptilting no doubt produced fissures and faults that directed 

 the early lines of drainage. 



^ See W. Whitaker, On Subaerial Denudation, G. Mag. 1S67 (paper reprinted 

 with additions). 



2 See also S. V. Wood, jun., Phil. Mag. 1864, G. Mag. 1881, p. 502. 



