JOG INTRODUCTORY REMARKS ON 



slate. The subdivision here entitled the Quartz isles, com- 

 prises the chain of Lunga, Scarba, Jura and Isla ; to which 

 Colonsa, Oransa and the Garvelach isles may be added ; the 

 principal chain being characterized by the prevalence of 

 quartz rock, and the other islands being evidently connected 

 with it by community or alternation of its other leading 

 strata. The last subdivision includes, together with Shuna, 

 the Craignish isles, the isles of St. Cormac, Gigha, and 

 Cara, and is distinguished by a series of schistose rocks 

 in which chlorite schist predominates, and which occupies 

 an extensive tract on the adjoining mainland. It will 

 be convenient to discriminate it from the other groups by 

 the name of the Chlorite isles. 



The islands of Kerrera and Seil form the immediate 

 bond of union between Mull and the Argyllshire coast, 

 containing the trap rocks of the one and the schistose 

 strata of the other. A very small portion also of secondary 

 strata, occurs in the three northernmost, but in parts so 

 detached and minute, that they almost disappear in the 

 particular details. The most obvious feature of the con- 

 nexion will be seen to consist in the trap which prevails 

 in the northernmost islands and on the shores of the 

 mainland immediately opposed to them. The rocks of 

 this family, from their analogy in position, correspondence 

 in structure, and geographical proximity, seem to be 

 detached parts of the trap of Mull and Morven, as I 

 formerly had occasion to remark. The intermediate rocks 

 and islets, otherwise little worthy of notice, become in 

 this respect interesting, as serving to connect by some 

 intermediate points, the leading masses which form the 

 principal islands, whether belonging to the one set of 

 rocks or the other. With this view nearly the whole 

 of them were examined ; a task rendered very difficult 

 by the strength and rapidity of the tides, the boisterous 

 nature of this sea, and the consequent difficulty of land- 

 ing ; circumstances which present the only apology that 

 ought to be offered for the imperfections which may 



