Ch. VI.] 
VOLCANIC ROCKS— VAL DI NOTO, 
69 
vesicles are occasionally empty, both in dikes and currents, 
and are in some localities filled with calcareous spar., arragonite, 
and zeolites. The structure is, in some places, spheroidal, in 
others, though rarely, columnar. I found dikes of amygda- 
loid, wacke, and prismatic basalt, intersecting the limestone at 
the bottom of the hollow, called Gozzo degli Martiri, below 
Melilli. 
Dikes. — Dikes of vesicular and amygdaloidal lava are also 
seen traversing peperino, west of Palagonia, near a mill by the 
road side. 
No. 6. No. 7. 
Horizontal section of Dikes near Palagonia. 
a, Lava. 
b, Peperino, consisting of volcanic sand, mixed with fragments of lava and 
of limestone. 
In this case we may suppose the peperino to have resulted 
from showers of volcanic sand and scorise, together with frag- 
ments of limestone thrown out by a submarine explosion,, 
similar to that which lately gave rise to the volcanic island off 
Sciacca. When the mass was, to a certain degree, consoli- 
dated, it may have been rent open, so that the lava ascended 
through fissures, the walls of which were perfectly even and pa- 
rallel. After the melted matter that filled the rent had cooled 
down, it must have been fractured and shifted horizontally 
by a lateral movement. 
In the second figure, No. 7, the lava has more the appear- 
ance of a vein which forced its way through the peperino, avail- 
ing itself, perhaps, of a slight passage opened by rents caused 
by earthquakes. Some of the pores of the lava, in these dikes, 
are empty, while others are filled with carbonate of lime^ 
