NORTH UIST. GEOLOGY. 143 



whose ardour is apt to flag in searching for novelty 

 which he is doomed not to find ; and they re-excite 

 his languid endeavours to watch with renewed attention 

 for changes which, though at the moment concealed 

 from him, may possibly be on the brink of rewarding 

 his labours. The ridge of Heval is an Oasis in the 

 desert of gneiss,* and independently of this merit, it 

 possesses that interest arising from obscurity which never 

 fails to rouse the attention. 



The aspect of the surface of this ridge and the cha- 

 racter of its outline are so precisely similar to that of 

 the island in general, that an observer, contented with 

 a superficial view, would without hesitation note it as 

 formed of the same rock. It offers a strong example 

 of the necessity which the geologist is under of taking 

 nothing on trust, and of concluding nothing from in- 

 duction when the evidence of contact can be obtained. 

 The account of the ridge of Heval will be rendered 

 more intelligible by disturbing the geographical order 

 of this description ; and the reader will thus gain a 

 key to solve difficulties which were to me a source 

 of much research and trouble. 



It was shown that North Uist is separated at its 

 southern extremity from Benbecula by a complicated 

 strait; improperly called Loch Rueval, since it has a 

 free communication with the sea at both ends. This 

 passage is strewed with a multitude of islands, Grimsa, 

 one of the principal, having already been mentioned under 

 the head of Benbecula, on account of its geographic re- 

 semblance, as well as its physical identity. Many more, 

 which I have thought it unnecessary to notice, such 

 as Flodda, Bent, Broad Isle, and others whose names 

 are scarcely known, belong like Grimsa to this division ; 

 consisting of gneiss, and resembling their parent Ben- 

 becula in every particular. But the hilly island Rona, 

 together with its dependencies, Flota beg, Flota more, 

 and others of minor note, are distinguished from these, 



