134 SEIL. GEOLOGY. 



matter. The existence of bituminous matter in crystalline 

 limestones is no objection to this view ; but rather tends 

 to confirm it ; as there is little doubt that these also are 

 portions of conchiferous beds which have undergone 

 essential changes of structure ; losing the forms of the 

 bodies which they contained, but preserving a portion at 

 least, of the constituent ingredients. 



There is nothing to add respecting the small island of 

 Eysdill, which may be considered, geologically, as form- 

 ing a portion of Seil, being separated from it by a very 

 narrow strait. The reputation of its slate quarries is far 

 spread, and its features present nothing which has not 

 been already stated in considering the principal island. 



I may terminate this account of Seil by remarking that 

 some detached islets at its northern extremity consist of 

 trap, as is indicated in the map that illustrates this 

 description. 



