VIEWS OF ENGLISH WRITERS. 381 



On later pages (137 and 138) the author continues : 



"The table-land of the Highlands has been the work not of subterranean action, 

 but of superficial waste. The long flat surfaces of the Highland ridges, cut across 

 the edges of the vertical strata, mark, I believe, fragments of a former baselevel of 

 erosion. In other words, they represent the general submarine level to which the 

 Highland region was reduced after protracted exposure to subaerial and marine 

 denudation. The valleys which now intersect the table-land . . . have been 

 eroded out of it. 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 ; . . . and in this rolhng plain we should find a 

 restoration of the bottom of a very ancient sea. ... Its mountains were levelled ; 

 its valleys were planed down ; and finally the region was reduced to a baselevel 

 of erosion beneath the waves. . . . Some central tracts of higher ground may 

 have been left as islands." * 



In Geikie's " Text-book of Geology " subaerial denudation is regarded 

 as providing a greater amount of detritus than marine denudation, and 

 a significant modification is made of Ramsay's interpretation of plains 

 of marine denudation. In the actual production of such plains — 



'• The sea has really had less to do than the meteoric agents. A ' plain of marine 

 denudation ' is that sea-level to which a mass of land had been reduced mainly by 

 the subaerial forces, the line below which further degradation became impossible, 

 because the land was thereafter protected by being covered by the sea. Undoubt- 

 edly the last touches in the long process of sculpturing were given by marine waves 

 and currents, and the surface of the plain, save where it has subsided, may corre- 

 spond generally with the lower limit of wave action." f 



Plains or peneplains of subaerial denudation, elevated into a new cycle 

 of erosion without waiting to be planed oft' by the sea, are not explicitly 

 considered. Under '' terrestrial features due to denudation " it is stated 

 that — 



"Table-lands may sometimes arise from the abrasion of hard rocks and the pro- 

 duction of a level plain by the action of the sea, or rather of that action combined 

 with the previous degradation of the land by subaerial waste. Such a form of sur- 

 face may be termed a table-land of erosion^' (page 939). 



*I have elsewhere (London Geographic Journal, vol. v, 1895, p. i;]9) taken the liberty of ques- 

 tioning the geological date assigned by GeiKie to this baseleveiing. He states that " the great 

 denudation which leveled the old Highland table-land was far advanced before the close of the Old 

 Red Sandstone period" (page 14:4). Undoubtedly a vast denudation was accomplished before 

 and during that time, for the heavy strata of the Old Red lie on the greatly denuded edges of 

 more ancient rocks; but the even table-land, restorable from the summits of the mountains and 

 ridges of today, seems to be of more modern date, because, since the deposition of the Old Red, 

 significant deformation has taken place, whereby a peneplain of earlier date must have been here 

 elevated, there depressed. Tlie table-land now recognizable appears to be the result of denuda- 

 tion on the deformed Old Red peneplain. There has been plenty of time for its production. 



t Second edition, 1885, pp. 434, 435, 



