440 DOMAIN XII. VOLCANIC. 



lowing its direction; in which laborious em- 

 ployment a number of men are occupied for 

 whole weeks, the vein being sometimes a hun- 

 dred and fifty, two hundred, or even three hun- 

 dred feet long, and large in proportion. These 

 veins are called Faraglioni. I have examined 

 them, and satisfied myself that the accounts I 

 received were true. Pumice-dust, and large 

 heaps of the first species of pumice, with some 

 scattered vitrifications, usually cover these veins, 

 which, when viewed with the attentive eye of 

 the naturalist, give reason to believe that they 

 are long tracts of pumice, which once flowed in 

 Currents, a liquid state. Their bubbles, frequently length- 

 ened in the direction of the vein, seem likewise 

 to prove the same. 



" M. Dolomieu, who first suggested that many 

 pumices have flowed in currents like lavas, ob- 

 served that at Campo Bianco the lighter pumices 

 lie above the heavier ; in the same manner as in 

 the common currents of lava, the porous lavi 

 occupy the highest place. I have certainly ol 

 served this disposition ; but sometimes it prov( 

 fallacious : for if the excavation be continue* 

 below the vein which forms the second species 

 of pumice, we frequently again find masses of 

 extremely light and pulverulent pumice. 



c The first action of the fire of the furnace 



