

316 DOMAIN XII. VOLCANIC. 



nets, from Vesuvius. The appearance is rather 

 vitreous. 



HYPONOME II. POROUS BASALTIN. 



The three very compact homogenous .lavas of 

 Dolomieu are probably original rocks; for he 

 speaks of their occurrence in blocks* ; and the 

 grand error of his volcanic treatises is, that he 

 confounds antecedent rocks and ejections with 

 lavas. 



The siderous compact lavas are thus described 



by Brochant ; who has, however, in this part of his 



valuable work, followed the arrangement and 



ideas of Dolomieu. 



Brochant's " These lavas are commonly of a black colour, 



account. 9 ' 



more or less deep, seldom grey or brown : their 

 fracture is imperfectly conchoidal, their contexture 

 very compact ; they are harder, but more brittle 

 than trap, rather sonorous, very heavy ; they melt, 

 under the blow-pipe, into black scoriae ; they at- 

 tract the magnet ; they give, by breathing on them, 

 an earthy smell : this lava is one of the most 

 common in volcanic regions, above all in the cur- 

 rents which have issued from Etna, and which are 

 almost entirely composed of it. 



* Etna, 185. 



