OP THE WESTERN ISLES OF SCOTLAND. 385 



He inquired it' it were possible to get a connecting-link between 

 the amphibole- and pyroxene-andesites. 



Mr. Cole, speaking of the dykes and sheets traversing the 

 plateau-basalts, inquired whether those with selvages of tachylyte 

 might be related to the later audesitic eruptions. 



The Author, in reply to Mr. Barrow, said that the existence of true 

 amphibole-andesites was shown, even when the change was most 

 complete, by the chlorites &c. occupying the place of the original 

 hornblende-crystals showing traces of the '' resorption halos " so 

 characteristic of that mineral. He had described rocks which 

 contain amphibole, mica, and pyroxene ; but in the district under 

 consideration the distinction between amphibole- and pyroxene- 

 andesites may be fairly made out. In reply to Mr. Cole, he was 

 not aware of any andesitic dykes traversing the basalts which 

 put on a selvage of tachylyte. 



