DOMAIN XII. VOLCANIC. 305 



cools slowly, and condenses under the forms 

 to which its nature tends*. For what is 

 crystallisation but the effect of a similar in- 

 clination of the more simple, similar, and 

 attenuated particles of matter? It appears 

 to me then that this tendency, being faci- 

 litated by the circumstances here indicated, 

 explains the formation of prismatic lavas, 

 without confounding them with the pro- 

 ducts of crystallisation/'-^ 



As an example, he mentions the rock 

 of Motta, which with those of the Cyclops 

 he has also engraved, in the rude manner 

 now practised in Sicily. He observes that, 



* " A similar combination, upon a very small scale, may have pro- 

 duced the few prisms which are found in the upper parts of Etna, 

 and likewise in the Eolian Isles, not to mention Vesuvius." 



Our author has shown that schistose substances, when melted by 

 the volcanic heat, will reassume the same form. But what does he 

 conceive to be the natural tendency of basaltin ? The forms he de- 

 scribes, are not only the prismatic with articulations, but that of 

 balls with concentric layers j and others, in which the prisms con- 

 tract and meet in the centre, like the balls of pyrites found in chalk. 

 But as iron often assumes the prismatic and globular forms, and 

 even the radiated and concentric, he ought to have referred the 

 whole to that metal, so predominant in siderite, which forms the 

 base of these lavas. 



t P. 31Q. 



VOL. II. X 



