ISLA. GEOLOGY. 253 



prevented by the peculiar form of the limestone mass 

 of Isla, and the prolongations of the strata do not 

 admit of the same adaptation. Neither could it be ex- 

 pected ; since the two points are so far asunder that 

 the obliteration and renewal of the calcareous strata 

 may occur in the interval, and many derangements of 

 the line of bearing may also take place, which from the 

 nature of the adjoining country do not admit of examina- 

 tion. Yet it must be remarked, that as the bearing of 

 the strata in Kerrera, as far as they can be ascertained, 

 and the general outline of that island, are more northerly 

 than in Seil, it is probable that the strata of Lismore 

 undergo a flexure in a line parallel to the latter island, 

 which, with the others to which they are subjected in their 

 course to Isla, will bring them within the limits required 

 for establishing the species of continuity in question. 

 The rocks in both islands are identical in character and 

 composition ; and, together with the circumstances now 

 pointed out and those which have preceded, will, even 

 if judged insufficient to prove the identity of these strata, 

 serve to illustrate the connexion of the blue limestone 

 of Isla with the approximate schists. Thus, like that 

 lately discussed, it will find its place among the general 

 series of these schistose rocks ; while the irregularities that 

 accompany it may possibly hereafter disappear, or at 

 least be materially diminished when it shall be examined 

 by some future geologist with the clue here afforded. 

 My own examination of Isla having preceded that of all 

 the other Schistose islands, was deprived of this assist- 

 ance : had they been examined in the order in which 

 they have been described, many of the difficulties which 

 were encountered would not have occurred. 



The last rock which remains to be noticed, is that 

 anomalous rock of porphyritic aspect already mentioned in 

 the account of Jura; and of which considerable masses 

 are to be seen in the neighbourhood of Kildaltori on the 

 eastern shore. This forms a range of craggy eminences, 



