DOMAIN XII. VOLCANIC. 



a lens*/' In this they differ from basaltin, 

 one of the most compact substances in na- 

 ture; though Werner himself marks its con- 

 texture as cellular, or vesicular. Even in 

 the purest substances, as glass, the marks 

 of fusion by heat remain in little globular 

 cavities. But that the question has not 

 been examined with due care and sagacitj^ 

 will appear from another observation. 



The beautiful forms of basaltic columns Basaltic co. 



lurans corn- 



have, on a first review, been compared 

 with the fissures arising from the desicca- 

 tion of starch, and some argillaceous sub- 

 stances. But the comparison is in fact of 

 the most careless kind, and arises from a 

 distant resemblance, as if a trunk of a tree 

 were compared with a Corinthian column. 

 The accurate eye of Pictet has observed, 

 and he has engraved a most distinctive 

 characteristic of the columns of the Giants 

 causey, unobserved by all writers on the 

 subject ; which is, that the joints of the 

 columns are not only inserted in each other 



* Etna, p. 192. 



