an Eruption of Mount Vefuvius. 77 
full of cracks, from which there iffues a conftant ful- 
phureous fmoke that tinges them and the circumjacent 
fcoria and cinders with a deep yellow, or fometimes a 
white tint. Thefe laft mentioned cracks, though deep, 
do not, as I apprehend, pafs the Jlratum formed by the 
laft eruption, and which, from its extreme thicknefs, 
particularly in the valley, will probably retain a great 
degree of heat for fome years to come, as did a thick 
Jlratum of lava that ran into the fojfa grande in the year 
1767. 
The number and fize of the ftones, or, more properly 
fpeaking, of the fragments of lava which have been 
thrown out of the volcano in the courfe of the laft erup- 
tion, and which lie fcattered thick on the cone of Vefu- 
vius, and at the foot of it, is really incredible. The largeft 
we meafured was in circumference no lefs than one hun- 
dred and eight Englifh feet, and feventeen feet high. It 
is a folid block, and is much vitrified : in fome parts of it 
there are large pieces of pure glafs, of a brown yellow 
colour, like that of which our common bottles are made,, 
and throughout its pores feem to be filled with perfect, 
vitrifications of the fame fort. The fpot where it 
alighted is plainly marked by a deep impreffion almoft 
at the foot of the cone of the volcano, and it took three 
bounds before it fettled, as is plainly perceived by the 
marks 
