NOME II. VESICULAR LAVA. 33 J 



every step sank deep into it. The figure of these 

 scoriae, the smallest of which are about a line, 

 or somewhat less, in diameter, is very irregular. 

 Externally they have the appearance of scoriae 

 of iron ; and when broken, are found full of 

 small cavities, which are almost all spherical, or 

 nearly of that figure. They are therefore light 

 and friable, two qualities which are almost 

 always inseparable from scorias. This great 

 number of cavities is an evident proof of the 

 quantity and vigorous action of the elastic fluids, 

 which in this eruption, imprisoned in the liquid 

 matter within the crater, dilated it on every side, 

 seeking to extricate themselves ; and forced it, 

 in scoriaceous particles, to various heights and 

 distances, according to the respective weights of 

 those particles. The most attentive eye cannot 

 discover in them the smallest shorl ; either be- 

 cause these stones have been perfectly fused, 

 and with the lava passed into homogenous con- 

 sistence, or because they never existed in it. 

 Some linear felspars are however found, which 

 by their splendour, semitransparency, and so- 

 lidity, show that they have suffered no injury 

 from the fire. When these scoriae are pulverized, 

 they become extremely black ; but retain the 

 dryness and scabrous contexture which they had 

 when entire. They abound in iron, and in con- 



