498 



DOMAIN XII. VOLCANIC. 



its cavities, and often also intermixed with mica. 

 Near the orifices of the volcano detached crys- 

 tals of augite are found in abundance ; they be- 

 long to those drosses and porous lavas, which the 

 violence of the vapours, in the vicinity of the 

 mouths, has decomposed without affecting the 

 augite." 



From the description of this celebrated vol- 

 cano it is now proper to pass to its most pecu- 

 liar production. 



HYPONOME I. LAVA WITH LEUCITE. 



This abounds in the neighbourhood of Vesu- 

 vius, particularly in the more ancient eruptions ; 

 or pompeia. and the streets of Pompeia, built when that vol- 

 cano was extinct, were found to be paved with 

 this lava. Breislak employs a chapter in the dis- 

 cussion of leucite, which is common in the an- 

 cient lavas of the territory of Naples and Rome*. 

 There is an immense quantity of leucites in the 

 Aibano, mountains of Albano, Tivoli, Caprarola, Viterbo, 

 Aquapendente, Civita Castellana, and Borghetto, 

 They often occur in compact lava, sometimes in 

 the vesicular, and even in the dross, which de- 

 composing, leaves the crystals separate. They ar 

 in the calcareous rocks of Somma, whioi 



* Voyage dans la Campanie, teme ii. 



