138 LUIXC;. c; to LOGY. 



its natural division into prismatic fragments, and the 

 strata that accompany it, resemble in every point those 

 circumstances as they occur in the corresponding ridge in 

 Seil, and, for the same reasons, it is here unnecessary 

 to dwell on them. This series does not extend throughout 

 the whole island, but terminates towards the middle, 

 where the high grounds subside into the lower tract, 

 and apparently where the change of direction in the 

 strata takes place. 



This collection of strata is also followed, as in Seil, 

 by clay slate; the beds above it having generally also 

 a lower elevation than those below. In this portion 

 of the clay slate one of the principal varieties is found ; 

 and it is most abundant at the southern extremity of 

 the island. This consists in the passage of the ordinary 

 clay slate into drawing slate ; a circumstance which also 

 occurs, even more abundantly, in Torsa. This substance 

 rarely, if ever, acquires the degree of softness which 

 characterizes real specimens of that mineral ; but many 

 parts are sufficiently tender to leave their trace on paper. 

 It occasionally contains mica, and pyrites, but the latter 

 is much. more rare than in the ordinary schist. 



Among the beds now described are found thin strata 

 of black and of grey limestone, intermingled and alter- 

 nating with them in the manner usual with those limestones 

 which occur among the schistose rocks. In colour, and 

 indeed in general aspect, the two are sometimes not to 

 be distinguished, so that on a cursory view the calcareous 

 rock might be easily overlooked. These beds terminate 

 the island in an eastern direction ; being succeeded by 

 the narrow strait that separates it from Shuna. In a 

 geological view however, the strata of this island must 

 be considered as succeeding those of Luing ; the dip 

 and direction being as regular and uniform as they 

 will hereafter be found throughout all the islands con- 

 nected with the Argyllshire coast, as well as in the 

 mainland itself. 



