INTRODUCTORY REMARKS, &C. 105 



INTRODUCTORY REMARKS ON THE SCHISTOSE 

 ISLANDS. 



BEFORE proceeding to the description of the different 

 islands which compose this group, it will be useful to 

 take a general view of the whole ; reserving the comparison 

 of the results deducible from their physical history and 

 geographic connexions, until they have been all examined. 

 Their strong resemblance to each other in structure, the 

 obvious repetitions of similar strata which occur through- 

 out them, the mutual correspondence of their outlines 

 and of the bearings of their strata, together with the 

 intimacy of their geographical positions, render this asso- 

 ciation as natural as it is useful for the illustration of 

 each individual and the comparison of the whole. If 

 a few of the rocks occurring in these islands do not 

 possess the schistose structure, that term is, nevertheless, 

 scarcely exceptionable ; since they chiefly consist of those 

 primary stratified rocks, namely, micaceous schist, quartz 

 rock, argillaceous schist, chlorite schist, and other asso- 

 ciated substances, which all, in a greater or less degree, 

 present the schistose character. Although the whole of 

 this group thus possesses a common character, it is further 

 divisible into portions, each of which is distinguished by a 

 common bond of resemblance that does not pervade the 

 remainder ; one only, Lismore, being excluded from either 

 of these subdivisions. 



The first of these subordinate divisions may be desig- 

 nated by the name of the Slate isles, and it includes 

 Kerrera, Seil, Luing, and Torsa; Shuna, which is geo- 

 graphically and popularly associated with these, apper- 

 taining, in geological character, to the third subdivision. 

 The characteristic of this group, is the prevalence of clay 



