GUILLEMON. GEOLOGY. 423 



respect from those already described, it is superfluous to 

 dwell on them; the object of a visit to Pabba being 

 accomplished in the determination of its identity with 

 those strata of Sky with which, from the general dispo- 

 sition of the rocks of that island, it ought to correspond. 



I may add that the trap veins of this island are par- 

 ticularly conspicuous as well as numerous ; the former 

 circumstance arising naturally from their superior perma- 

 nence when contrasted with the very tender and yielding 

 nature of the shale that encloses them. 



I was induced to examine Guillemon from the expecta- 

 tion of finding the limestone which is wanting to connect 

 the neighbouring shore of Scalpa with Pabba. In this 

 I was disappointed, since it proved to be an entire mass 

 of greenstone. 



This small island is about forty or fifty feet in height and 

 abrupt all round. The substance of which it is composed 

 corresponds in every respect with the name, since the horn- 

 blende and felspar have both a green colour. The pre- 

 dominance of similar rocks on the neighbouring shores of 

 Sky, and their occurrence in Scalpa, leave no doubt 

 respecting the geological connexion and position of this 

 rock; which doubtless reposes on the limestone it has 

 here concealed from view. 



