( IS ) 



'when its violence had ceafed, the more 

 heavy bodies mufl have fubfided to the 

 bottom in obedience to the law of gravity, 

 the lefs heavy have remained above them, 

 and the lighteft have occupied the higheft 

 place; which, however, is not the fad:, 

 fmce, as we fhall fee, at a fmall depth within 

 the tufa, are found large mafles of lavas, 

 enamels, and glafles. But it does not ap~ 

 pear to me improbable that thefe mafles 

 may have been thrown out from fome 

 burning mouth, after the hardening of the 

 tufa, within which they have not penetrated 

 deep. 



Not only the pbfition and winding eourfe 

 of this tufa over the back and fides of the 

 mountain fufficiently prove that it once 

 flowed : its very nature is a ftrong confir- 

 mation of this fad. It is not an aggrega- 

 tion of aflies and fand ; a mixture of frag- 

 ments of Ihoerls, feltfpars, and lavas de- 

 compofed, and rendered earthy, and faften- 

 ed together by the adion of the water, be- 

 coming fo hard as to be cut into pieces pro- 

 per 



