356 Miocene Denudations. 



Scuir of Eigg, the lava (obsidian 3, fig. 77) flowed over 

 the valley gravel (2 ) and buried it. Since then the waste 

 has been so great, that the destruction of the older hills 

 that bounded the valley has literally exalted the valley 

 and laid the hills low, for the obsidian was harder than 

 the walls of the valley, and has longer resisted destruc- 



FIG. 77. 



1. Old lavas, &c. 2. River valley scooped out by denudation. 

 3. Obsidian filling valley. 4. Present outline of the country 

 produced by later denudations. 



tion, and thus it happened that the Scuir of Eigg 

 became one of the most striking peaks in the Western 

 Islands. 



Thus it also happens that in the old volcanic plateaux 

 valleys a thousand feet deep have been excavated, and 

 the whole region has by denudation been changed into 

 a line of fragmentary islands, the high sea cliffs of 

 which attest the greatness of the waste they have in 

 time undergone. 1 



During this time the greater contours of England 

 remained the same, that is to say, the old mountain 

 lands of Devon, Wales, and Cumbria, though suffering 

 from denudation, remained mountainous still, and, 

 together with the lower country, the whole was merely 

 upheaved so far that England was joined to the Con- 



1 See A. Geikie, 'Jour. Geol. Society,' xxvii., 'On Tertiary 

 Volcanic Rocks.' 



