56 COLONSAY 



Sligachan and Broadford have been similarly formed of 

 granophyre and allied rocks striking examples of the peculiar 

 contour assumed by the particular varieties of rock of which 

 they are composed. There are large areas of Torridonian 

 sandstone, much like that of Colonsay, in the south of Skye ; 

 and the neighbouring isles of Soay, Scalpay, and part of 

 Eaasay are mainly formed of it. 



Torridonian sandstone is the principal rock in the 

 northern half of Eum. The higher mountains of the 

 southern portion of the island are composed of gabbro. 

 Quartz-porphyry and allied rocks enter into the formation of 

 the western side ; while gneissose rocks, recently shown by 

 Mr Barker to be of Tertiary age, are much in evidence in 

 the south-east. The isles of Canna, Muck, and Eigg mainly 

 consist of basaltic lavas. 



Mull, like the northern part of Skye, is mostly Tertiary 

 volcanic rock. Deep layers of lava flows appear to cover 

 remains of the Mesozoic period. The mountains north of 

 Lochbuie are composed of gabbro ; while Ben Mor, the highest 

 mountain in Mull, is formed of bedded lavas. Granite 

 appears over a large area of the Eoss of Mull. It is quarried, 

 and has been largely employed in structures requiring great 

 strength. Du Hirteach and Skerryvore lighthouses, Black- 

 friars Bridge, Holborn Viaduct, Thames Embankment, and 

 the Prince Consort Memorial, Hyde Park, are well-known 

 structures for which this stone has been used. 



The landscape of the basaltic differs greatly from that of 

 the gneissose and schistose islands. The regular terraced 

 formation and beautiful green-verdured slopes, such as are 

 to be seen in Mull and the north of Skye, pleasingly 

 contrast with the irregular ruggedness of the Outer and 

 South Inner Hebrides. As the decay of the rocks furnishes 

 a rich loam which supports a luxuriant growth of grass, the 

 basalt districts are distinguished by their greenness even 

 up to the tops of the hills. 



