NOME V. PUMICE. 439 



my description to be as clear and explicit as 

 possible. It has been already said, that many 

 lavas, and other volcanic productions, on re- 

 fusion, become cellular. To apply this to the 

 pumice in question, would be an error. A lava, 

 which has undergone this change by the action 

 of elastic gases, continues to form one whole, 

 though interrupted by these multiplied pores. 

 The pumice of which I now speak is princi- 

 pally formed by an accumulation of small vitre- 

 ous vesicles, which attached themselves to each 

 other while they were yet soft from the action of 

 the fire ; and which, from their globose figure, 

 not adhering except in a few points, have left 

 many vacuities very visible in the fracture of the 

 pieces. The labourers who dig these pumices, 

 after they have shaped them into parallelepipeds, 

 take them on their backs and carry them down 

 to the shore, where they pile them up in large 

 heaps, to be ready for sale when opportunity 

 shall offer. We are not to imagine, however, 

 that this species of pumice is to be found in 

 every part of the mountain : the workmen, to 

 find what they call the vein of it, are obliged to 

 make great excavations, and frequently without 

 success; which, as they told me, in this case, as 

 in fishing for coral, often depends on chance. 

 When they have found the vein, they dig it, fol- 



