204 COLONSAY 



flowed to the lowest level, where it gradually cooled and 

 hardened. It blocked and filled up the river bed, covering 

 the sandstone, forests of pine, and other debris that in 

 later ages were destined to shed light on the geological 

 history of the islands. The land that once united the 

 basalt plateaux of Eigg to the Cambrian sandstone 

 mountains of Rum, from which drained a large volume of 

 water such as must have flowed along the old river course, 

 has disappeared, and Eigg has become an island. The 

 ascending sides of the valley in which the Sgurr at one time 

 reposed have been worn away, and are now reduced to slopes 

 which shelve steeply down to the shores. That land, we 

 are told, was one of rich alkali -charged soil ; and the buried 

 leaves of Canna and Mull and the pines of Eigg indicate a 

 period of warmer climate than we now enjoy. 1 



1 Sir A. Geikie's beautiful theory of the Sgurr of Eigg, given above, 

 has recently been challenged by Mr Harker. It seems likely now that 

 the pitchstone was intruded underground and never reached the surface 

 until laid bare by denudation. It may be noted that this later 

 interpretation makes a greater demand upon erosion than even its 

 predecessor. 



