108 RAMBLES OF A NATURALIST. 



Without, however, having left the district of Ca- 

 tania we had found ample opportunity of ascertaining 

 the force of the volcano, and verifying the truth of 

 the descriptions which we had read of its destructive 

 action. To the north and to the west of the town 

 we had beheld the lava beds, which threw down and 

 crossed the ramparts, and to the south we had been 

 able to trace the course of those undulating streams 

 which overtopped the walls that had been con- 

 structed by Charles Y. We had seen the for- 

 midable thickness of this destructive stratum on 

 descending the stairs of the Pozzo di Vela, a sort of 

 well hollowed out in the direction of the outer side 

 of this wall, at the base of which Prince Biscari has 

 found the bed of the river Amenano,* which dis- 



* The river Amenanus of the ancients. This part of the town 

 presents a very curious aspect. The lava, which reached to the 

 level of the parapet, only flowed over it at a few points ; a circum- 

 stance which shows us very plainly the mode in which the stream pro- 

 gressed. The lava did not flow along the wall like a fluid or 

 viscous liquid, but formed a sort of irregular pyramid, whose base 

 rested against the wall, and whose lateral slopes exhibited as great 

 an inclination as a steep flight of stairs. The lava consequently 

 comported itself very much in the same manner as any mass of solid 

 matters when thrown down an incline. 



These facts do not harmonise with the ideas which are commonly 

 entertained in reference to the nature of lavas generally, more 

 especially with respect to their cohesion. Lava streams very rarely 

 preserve their fluidity for any length of time, for on being brought 

 into contact with the air, their surfaces harden and offer very great 

 resistance, even while they are- flowing with considerable rapidity. 

 M. Blanchard and myself were enabled to confirm these facts within 

 the crater of Vesuvius. On throwing with all our force several 

 porous stones upon a current of lava which had burst forth at a few 

 paces from us, and whose surface appeared perfectly smooth, we 



