CORRASION BY GRAVITY STREAMS. 313 



there and at Wastwater — cliffs produced by such peculiar 

 agencies that, upon exposure to atmospheric conditions, 

 they almost bury themselves with screes in establishing 

 the "angle of repose" under present conditions — and at 

 valley constrictions ; consider also the weaker action in 

 forming the spur facets to be seen from the railway just 

 below Keswick, and the absence of such forms still lower 

 down in the valley "broads." 



The writer understands that Professor Marr is about to 

 deal with this area in detail in the near future, hence the 

 very brief description here of both this and the associated 

 Pennine district. 



Scotland (Blair Atlwl). — Owing to the kindness of Pro- 

 fessor J. W. Gregory of Glasgow, the writer was enabled 

 to take part in one of his University field excursions to the 

 centre of the Highlands at Blair Athol last winter. 



General Topography, — The mountain peaks and plateaus 

 in the vicinity of Blair Athol represent the residuals of one 

 or two old surfaces of uncertain age, but evidently no older 

 in appearance than the dismantled Cretaceous or even 

 Tertiary land surfaces of the Eastern United States. In this 

 uplifted surface (or surfaces) a broad upland valley system 1 

 has been formed by ordinary streams. After elevation, 

 this surface was dismantled in turn by the development in 

 it of mature valley systems. Still later movements have 

 resulted in river revival accompanied by the excavation of 

 deep gorges. 



Glacial Phenomena. — Along the sides of a deep valley 

 such as the Glen Tilt for example, hanging valleys are a 

 common feature. Both the main and side valleys are long 

 and straight sided. Cirque forms also are present, and a 

 relatively strong facetting or planing action has apparently 

 occurred in the valley constrictions. 



1 By many physiographers this Upland Valley surface would be called 

 an immature Peneplain. 



