380 DAVIS — PLAINS OF MARINE AND SUBAERIAL DENUDATION. 



on during many oscillations of level, and the general result would hence be the 

 production of a great table-land, some parts rising gently to a height of many hun- 

 dred feet above other portions, yet the Avhole wearing that general tameness and 

 uniformity of surface characteristic of a table-land where there are neither any con- 

 spicuous hills tow^ering sharply above the average level nor any valleys sinking 

 abruptly below it. . . . The valleys which now intersect it . . . have 

 probably been dug out of it by the agencies of denudation. If therefore it were 

 possible to replace the rock which has been removed in the excavation of these 

 hollows the Highlands would be turned into a wide undulating table-land, sloping 

 up here and there into long central heights and stretching out between them league 

 after league with a tolerable uniformity of level. And in this rolling plain we 

 should find a restoration of a very ancient sea " (pages 106-108). 



On earlier pages, subaerial agents are described as producing valleys and 

 cliffs, Avhile the sea, aided by the atmosphere, produces a plain of marine 

 denudation. 



An essay " On modern denudation "* by the same author recognizes 

 that plains of denudation are reduced mainly by subaerial forces, but 

 concludes that '' undoubtedly the last touches in the long processes of 

 sculpturing were given by waves and currents, and the surface of the 

 plain corresponds with the lower limit of the action of these forces " 

 (page 186). 



In the second edition (1887) of this delightful book on the Scenery of 

 Scotland, argument is still directed against the prejudice that mountains 

 are due to local upheaval ; in a word, against the prepossession that moun- 

 tainous districts like the Scotch Highlands are constructional forms not 

 significantly modified by denudation ; but greater value is given to sub- 

 aerial agencies than before : 



"The more we consider the present operations of .sul)acrial denuding agents, the 

 more we shall be convinced that a system of hills and valleys, with all the local 

 varieties of scenic feature that now diversify the surface of the earth, may be 

 entirely pnKluced by denudation, without further help from underground forces 

 than the initial uplift into land. No matter what may be the original configura- 

 tion of the mass of land, the flow of water across its surface will inevitiibly carve 

 out a system of valleys and leave ridges and hills between them " (page 1)4). 



The possibility of producing a plain l)y a continuance of this process 

 is not here alluded to, but on an earli(ir page the aid of shore waves is 

 called on : 



"The limit beneath which there is little effective erosion ])y waves and tidal 

 currents probably does not exceed a very few hundred feet. Worn down to that 

 limit, the degraded land would become a submarine {)lain, across the surface of 

 which younger deposits might afterward be strewn " (page 92). 



* Trans. Geol. Soc. Glasgow, vol. iii, 18(38, p. 153. 



