Geological Origin of the Present Scenery of Scotland 



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so apt an instance of the meaning and results of the process of 

 denudation, that I have taken the subjoined drawing out of my 

 note-book and will briefly describe it. The Scuir of Eigg rises to 

 a height of nearly 1300 feet above the sea, and consists of two dis- 

 tinct portions. Of these, the lower is a mere swelling or ridge of the 

 general surface of the island, and, like die rest of that surface, is 

 composed of nearly horizontal sheets of dolerite, basalt, and other 

 varieties of the trap-rocks. Each of these sheets was originally a 





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l''u;. 5. — View of the Scuir of Eigg, from the east. — The lower part of the hill shews an older 

 series of gently inclined lava-beds, which had been hollowed out into a valley, wherein the 

 currents of pitchstone flowed that now form the vertical upper part of the hill. 



flow of lava, poured one over the other during a long course of 

 volcanic eruptions. At last this state of things ceased, and the 

 lava-flows began to be acted upon by the different forces concerned 

 in the process of denudation. The rock was gradually worn away, 

 layer after layer was laid bare, until at last a valley several hundred 

 feet deep was cut out of these old lava-streams. Its bottom was 

 occupied by a river which brought down rubbish from distant 



