126 The Founders of Geology LECT. 



stony substances, and occurs in volcanic countries/ but 

 the notion that it is itself of volcanic origin is quite 

 unfounded, because obsidian has never been observed 

 accompanying lava, because it is connected with basalt, 

 and because it contains a considerable portion of water of 

 composition, which is never the case with true volcanic 

 rocks." * If the questioner, still unconvinced, ventured to 

 present a piece of pumice, and point to its froth-like 

 structure and its presence in volcanic countries as evidence 

 of its former fusion, the answer would have been an equally 

 prompt and decided negative. Let me quote the actual 

 words of a Wernerian in reply. " It was formerly the 

 general opinion that pumice was a volcanic product, be- 

 cause it frequently occurs in countries conjectured to be of 

 igneous formation. It is now ascertained to be an aquatic 

 product, from the following facts : 1, It alternates with 

 Neptunian rocks, as basalt and porphyry ; 2, it is most 

 distinctly stratified ; 3, it passes into obsidian and pearl- 

 stone, and is thus connected with basalt, pitchstone, etc. ; 

 4, it contains water of composition, which is never the case 

 with true volcanic rocks ; 5, it has never been observed to 

 flow in streams from the crater or sides of a volcano, and 

 no one ever saw it forming a stream in countries containing 

 extinct volcanoes." 2 



Well might the inquirer retire in despair from such an 

 encounter. In vain would he have sought an explanation 

 of the origin of the vesicular structure of the rock, or 

 have asked how this structure could ever have originated 

 from an aqueous solution. He would probably have been 

 plied with a few more " facts " of equal veracity, and a few 



1 See Jameson, op. tit. p. 196. 2 Ibid. 



