222 Sir C. Lyell on the Conical Form of Volcanoes. 
melted matter, in the shape of dykes, as part of the cone-making 
process. 
But in place of this simple explanation of the phenomena, 
Von Buch substituted the following hypothesis: that a vast 
thickness of horizontal or nearly horizontal sheets of lava and 
a central axis towards all points of the compass, so as suddenly 
to uplift the whole stratified mass, making it assume a conical 
form ; giving rise at the same time, in many cases, to a wide and 
deep circular opening at the top of the cone, an opening called a 
“crater of elevation.’ 
In all great volcanoes of which sections can be obtained, there 
are some layers of compact stone, inclined at angles of 10°, 20°, 
and onto much higher angles, and these beds are often 
aqueou w eraibiey and the occasional steepness of the dips of cer- 
tain lavas, beyond that which is found on the flanks of ordinary 
cones, (many of which might have been assigned to local dislo- 
cation), afforded additional ti in favor of the new hy- 
is. The lecturer then gave a rapid review of the contro- 
versy respecting “craters of elevation,” stating the objections 
made to it by English and continental writers, including the late 
M. Constant Prevost; and he went on to observe that the princi- 
ar ani of this discourse was to show that the law laid down 
M. E. de Beaumont, and by the late M. Dufrenoy, as govern- 
eA the cooling and solidification of lava currents, on steep slopes, 
has no foundation in fact. Signor Scacchi had already, in 1855, 
seen ete described a compact stony lava which in that year had 
flowed down the flanks of Vesuvius from near the margin of 
at crater to the base of the cone in the Atrio del Cavallo, 
having a thickness of from 14 in the upper to 44 in its lower 
part, and dipping at angles varying from 32° to 38°. The i 
terior of this current was laid open to view ee a rare accident, 
