) 
Inward Alteration to be flopt, mult deviate through 
other PalTages under ground, heaping up continually 
Magazines lor a future Calamity. Now this combuftibfe 
matter feems to me to be nothing but Nitre mixt with 
feme other Minerals and Sulphur. ' He that has feen the 
way of making Sale- of Tartar by Deflagration, where 
you mix an equal quantity of pulveriz'd Nitre, has feen 
an exa£t Type of thefe burning Hills : For after each 
fpoonful you put into the burning Crucible, arifes firft a 
black thick Smoak. after which the fired Mineral boils 
up, as if it would over run the top of the Crucible. 
This I, take to be the matter. But, 2/y, How this Mo- 
tion of the Earth is performed is not fo eafily explicable, 
efpecially if one confiders, that the Motion of the Earth 
is not from the Perpendicular, but Horizontal Verte - 
'tis a Vibration fo quick, that it cracks the Giafs in the 
Windows : 'Tis difputable, whether the Reciprocations of 
a Lute- firing are more frequent. Now when the Vibra- 
tions are fo quick, and the Body mov'd fo great, the 
Motion muft be prodigioufly violent, and by conie- 
quence the Caufe, which I take to be nothing elfe but 
the aforefaid Vapours incens'd. We obferve the Thun* 
der, which is the effed: of the trembling of the Air, 
caus'd by the fame Vapours difpers'd through it, and en- 
countring one the other, has force enough to fliake our 
Houfes* And why their may'nt be Lightning and Thun- 
der under ground in fbme vaft Repofitories there > I fee 
no reafon, efpecially if we refled:, that the matter which 
compofes the noify Vapour above us, is in much larger 
quantities to be found under ground. Now if you ask 
me how this Horizontal Trembling is perform'd, (for 
fuch doubrieft it is, as appears by the Cracks in the 
Earth, which they fay, are to be found now all over 
Sicily) I can attribute it to nothing elfe but the furious 
Fajffageof the incens'd matter from one Grotto to ano- 
ther ;: For 'tis very probable thefe are continued in Tome 
parts 
