EFFECTS OF MINING. 
545 
iluid lava poured forth and flowed rapidly toward Paterno ; 
but the inhabitants of that place, not caring to sacrifice their 
own town to save Catania, rushed out in arms and put a stop 
to the operation.'’ * In the eruption of Yesuvius in 1794, the 
viceroy saved from impending destruction the town of Portici, 
and the valuable collection of antiquities then deposited there 
but since removed to Naples, by employing several thousand 
men to dig a ditch above the town, by which the lava current 
was carried off in another direction.f 
Effects of Mining . 
The excavations made by man, for mining and other pur¬ 
poses, may sometimes occasion disturbance of the surface by 
the subsidence of the strata above them, as in the case of the 
mine of Falilun, but such accidents must always be too incon¬ 
siderable in extent to deserve notice in a geographical point of 
view. Such excavations, however, may interfere materially 
with the course of subterranean waters, and it has even been 
conjectured that the removal of large bodies of metallic ore 
course of at least one hundred yards. At this distance, the suffocating, 
sulphurous vapors became so dense that I could follow the current no far¬ 
ther. The undulations of the surface were like those of a brook swollen 
by rain. I estimated the height of the waves at five or six inches by a 
breadth of eighteen or twenty. To the eye, the fluidity of the lava seemed 
as perfect as that of water, but masses of cold lava weighing ten or fifteen 
pounds floated upon it like cork. 
The heat emitted by lava currents seems extremely small when we con¬ 
sider the temperature required to fuse such materials and the great length 
of time they take in cooling. I saw at FTicolosi ancient oil jars, holding a 
hundred gallons or more, which had been dug out from under a stream of 
old lava above that town. They had been very slightly covered with vol¬ 
canic ashes before the lava flowed over them, but the lead with which 
holes in them had been plugged was not melted. The current that buried 
Mompiliere in 1669 was thirty-five feet thick, but marble statues, in a 
church over which the lava formed an arch, were found uncalcined and 
uninjured in 1704. 
* Ferrara, Descrizione deW Etna , p. 108. 
t Landgbebe, Naturgeschichte der VuVcane , ii, p. 82. 
35 
