84 . SUMMER ISLES. GEOLOGY. 



Carnisker alone, among the whole group, consists of 

 gneiss similar to that of Ru Carnderig, near which it lies. 

 The peculiarities of this gneiss have already been enume- 

 rated in the synopsis formerly given, so that it is here unne- 

 cessary to dwell on them. It is the variety characterized 

 by the predominance of compact felspar. 



It is scarcely necessary to distinguish the remaining 

 islands* in the geological description, as the same general 

 characters, with but little variation, are found in all. 



They all consist of a red sandstone similar to that of 

 Rasay and of the upper beds in Sky ; the finer kinds alter- 

 nating irregularly with the gravelly and conglomerate beds. 

 In respect to position, the strata present some circum- 

 stances requiring attention, on account of the deception 

 which they produce when seen from a small distance ; 

 the islands thus formed, appearing to consist of sandstone 

 reposing on gneiss. Eilan anaich, among others, offers 

 a good example of this peculiarity. The southern part 

 of that island consists of strata nearly horizontal, and 

 hence the surface in this quarter is a smooth grassy plain. 

 At the northern extremity, they are elevated into a posi- 

 tion highly erect, and often vertical, so as to produce 

 a rocky irregular surface; while the stratified character 

 nearly disappears ; the rock being split into confused frag- 

 ments of pyramidal and prismatic forms. Thus, even at 

 a short distance, the southern portion seems to repose in 

 an nnconformable manner on the northern ; and as the 

 same appearance occurs perpetually along this coast where 

 the sandstone reposes on the gneiss, it might easily be 

 registered as an example of this latter occurrence.f 



* The names of the principal islands are the following. Tanera, more 

 and beg, Muligrach, Ristle, Glasleak, more and beg, Eilan chlearach, 

 Eilan Dhu, Eilan anaich, E. Wheitancl E. Drum. 



f This fact presents additional evidence of the impossibility of deter- 

 mining the nature of rocks by the character of their outlines and dispo- 

 sition, even where these are within a small distance. It was not for 

 want of experience in these rocks that I first laid thorn down a* 



