GEOLOGICAL FORMATION 57 



The South Inner Hebrides consist, for the most part, of 

 a series of complicated and highly metamorphosed rocks, 

 known for the present as Dalriadian, from the ancient Celtic 

 kingdom of Dalriada. The islands form, as it were, the 

 south-western fringe of the zone of rocks belonging to this 

 group, which traverses the Central Highlands of Scotland. 

 Gigha, the most southern of the islands, is, like the adjacent 

 portion of Kintyre, mainly composed of quartzite and mica- 

 schist. The western part of Islay consists mostly of grits 

 and dark slates of the Torridonian system, with Lewisian 

 gneisses forming the Khinns. The central parts are mostly 

 slate, the north and east quartzite-schist. Broad belts of 

 limestone run between Portaskaig and the head of 

 Lochindaal. Portaskaig is well known to geologists also for 

 its conglomerates containing granite boulders. Jura and 

 Scarba are principally formed of quartzite-schist. The Paps 

 of Jura and the adjacent hills of Islay are among the finest 

 and most characteristic examples of quartzite rocks to be 

 seen in the Highlands. Luing and Seil are composed of 

 graphitic mica-schist and black slate, the latter being 

 worked ; Lismore and the Garvelloch Isles consist of lime- 

 stone, associated in the latter with Portaskaig conglomerate ; 

 Kerrera is composed of andesite (porphyrite), etc. 



The islands of Colonsay and Oransay were described by 

 M'Culloch as "extremely uninteresting in a geological view," 

 the predominant rock being micaceous schist ; but subsequent 

 investigations have discovered that there are other and 

 interesting varieties of rock entering into the structure of 

 these islands. Quite recent researches, by Messrs Wright 

 and Bailey of the Geological Survey, have brought to light 

 certain facts which may have an important bearing, not only 

 on the orogenic history of Colonsay, but also on that of the 

 Highlands in general. 



Geology, to the lay mind, is a somewhat abstruse subject, 



