288 PROP. W. MORRIS DAVIS ON [Aug. I9O9, 



perhaps trace the influence of Lyell and Murchison, who, pre- 

 sumably because of their intense interest in stratigraphy, gave less 

 attention than did their predecessors, Hutton and Playfair, to 

 problems of land-sculpture, and thus unconsciously diminished the 

 attention that might otherwise have been directed to the study of 

 laud-form under Ramsay's able leadership. 



VII. Ramsay's ' Plain of Denudation.' 



Whatever may be the causes that have directed the progress of 

 geological investigation in Great Britain, it appears to be true that 

 one may find a number of admirable studies on the stratigraphy, 

 palaeontology, and petrography of Wales, and yet that no one has in 

 the last half-century given close examination to the details of those 

 Welsh land-forms which led Eamsay to formulate his theory of 

 marine denudation over sixty years ago. One must still turn to his 

 original essay of 1846 for a description of the location, form and 

 altitude of so much of the ancient plain of denudation as is still 

 preserved : one looks in vain for any recent discussion of its verity, 

 of the process and date of its origin, of its extent, of its complete- 

 ness, of its unconsumed surmounting masses, of the date of its 

 uplift, of its present altitude in different localities, of its stage of 

 dissection in the present cycle of erosion, and of the shares that 

 normal and glacial agencies have had in its dissection ; and this, in 

 spite of Ramsay's declaration, cited at the beginning of this essay, 

 of the great interest that would be possessed by 



' a complete account of the denudations by which, after the disturbance of the 

 strata, Wales assumed its present form.' 



For our present purpose, it is comparatively immaterial whether 

 Ramsay's plain of denudation was of marine or of subaerial origin, 

 although I think that the evidence now in hand points to the latter 

 rather than to the former ; but the present altitude of the plain in 

 North Wales, the relation of the mountains to the plain, the date 

 of its origin, and the stage of dissection that it reached in pre- 

 Glacial time are of critical importance. Ramsay himself wrote, 

 regarding North Wales : — 



' There is indeed, on ascending a height, nothing more striking than the 

 average flatness of the tops of many of the hills ' (1866, p. 237 ; 1881, p. 329). 

 'All Wales shows this feature, from the Towey [in Carmarthenshire] to the 

 slaty hills that flank Cader Idris and the Arans [mountains soutb of Snowdon] 

 on the south and east, and even in the mountain land from Cader Idris to 

 the Menai Straits [North-West ern Wales], traces of a similar approximate 

 uniformity of height are plain to the experienced eye, showing the relics of an 

 old form of ground, in which deep valleys have been not rent but scooped out' 

 (1866, p. 238; 1881, pp. 329-30). 



It would appear that Ramsay clearly understood that the higher 

 mountains of North Wales had escaped complete destruction by 

 the agency which produced the plain : this impression is gained 

 on reading, after a statement of the enormous denudation that 



