Sir C. Lyell on the Conical Form of Volcanoes. 223 
namely, the sinking down in the same year (1855) of a certain 
portion of the north flank of the cone, whereby one side of the 
new lava stream was engulphed, and a section of the remainder 
rendered visible. Aiheuee this current had cooled on an aver- 
age declivity of 35°, it was as compact and as free from vesicles 
as many lavas which have congealed on level ground at the foot 
of Vesuvius, 
he first exemplification of a similarly inclined stony lava of 
known date on Mount Etna, described by the lecturer, and of 
which a pictorial representation was given, occurs in a ravine 
called the Cava Grande, near Milo, about 17 miles north of 
Catania, and 7 from the sea, above the level of which it is eleva- 
ted about 2000 feet. A branch of the lava current of 1689 
descending from the Val del Bove, cascaded over the right bank 
of that ravine 220 feet high, and on cooling, formed a tabular 
mass more than 16 feet in thickness, inclined at an average angle 
of about 35°, and concealing the face of the precipice for a width 
of about 400 feet. The internal structure of this new lava has 
Pin tag i by Sig 
cealed by the lay 
in 1857, a 
the early part 
as poured out in 
