GIG1IA AND CARA. GEOLOGY. 281 



sidered as parts of the same ridge. But there is one 

 doubtful circumstance in Cara, that cannot be passed 

 without notice. At its southern extremity the beds of 

 micaceous schist and quartz rock are immediately fol- 

 lowed by a mass, apparently of common greenstone, con- 

 sisting of an extremely hard and uniform basaltic base, 

 with occasional particles of felspar intermixed. This rock 

 has no tendency to the schistose fracture, and, notwith- 

 standing the similarity of the ingredients, is as much dis- 

 tinguished in aspect from any of the varieties of horn- 

 blende schist found in Gigha, as by its external features 

 and leading fracture, which display the vertical and 

 imperfectly columnar tendency so generally found in the 

 rocks of the trap family. The ambiguity respecting its 

 geological character arises from the circumstance of its 

 immediately following the micaceous schist in the same 

 order as the hornblende schist does in Gigha ; and from 

 the fact that the vertical prismatic fracture occurs, in other 

 instances, in those beds of which the alternation is unques- 

 tionable. That ambiguity must for the present remain, 

 since the peculiar characters of this series, as it occurs on 

 the adjoining continent, were not investigated until long 

 after the examination of these islands, and no opportunity 

 was afterwards afforded of re-examining Cara with the 

 increased knowledge derived from that investigation. 





