46 GEOLOGY OF THE CAMPSIE HILLS. 



In one part of this island, 1 discovered a great 

 accumulation of fragments of obsidian and of 

 pumice ; but these are two substances, which 

 some geologists will not admit to be of igneous 

 origin. With regard to this point in dispute, I 

 must here repeat what I have already observed in 

 another part of this memoir, that those who hold 

 obsidian and pumice not to be of igneous origin, 

 most certainly can never have trod true volcanic 

 ground. Proofs of these two substances being of 

 igneous origin, are to be seen upon Etna, Vesuvius, 

 and upon some of the Lipari Islands ; and those 

 proofs which I have there seen, appeared to me 

 so evident, that their origin could admit of no 

 dispute. One or two examples of these proofs, I 

 shall here beg leave to give, by copying some of 

 the notes which I took while on the Island of 

 Felicuda. Near the centre of the island, some- 

 what to the south-east of the principal mountain 

 which I have had already occasion to mention, I 

 discovered the remains of a crater upon an in- 

 sulated hill, which I found entirely formed of 

 different coatings of lava of various thicknesses. 

 In two different currents of the lava proceeding 

 from the broken crater of this hill, I observed 

 obsidian which had been in flow with the lava, 

 and now formed part of its congealed stream. 

 This obsidian when in mass, appeared almost black 

 and opake ; but, at the edges of its beautiful 

 donchoidal fracture, it was in some degree trans- 



