The nature of the noise
varies also very much, being either rolling, or rustling, or clanking like
chains when moved, or like near thunder, as, for instance, in the city of
Quito; or, lastly, clear and ringing, as if obsidian or some other vitrified
masses were struck in subterranean cavities. As solid bodies are excellent
conductors of sound, which is propagated in burned clay, for instance, ten
or twelve times quicker than in the air, the subterranean noise may be heard
at a great distance from the place where it has originated. In Caracas, in
the grassy plains of Calabozo, and on the banks of the Rio Apure, which
falls into the Orinoco, a tremendously loud noise, resembling thunder, was
heard, unaccompanied by an earthquake, over a district of land 9200 square
miles in extent, on the 30th of April, 1812, while at a distance of 632
miles to the north-east, the volcano of St. Vincent, in the small Antilles,
poured forth a copious stream of lava. With respect to distance, this was
as if an eruption of Vesuvius had been heard in the north of France. In the
year 1744, on the great eruption of the volcano of Cotopaxi, subterranean
noises, resembling the discharge of cannon, were heard in Honda, on the
Magdalena River. The crater of Cotopaxi lies not only 18,000 feet higher
than Honda, but these two points are separated by the colossal
p 209
mountain chain of Quito, Pasto, and Popayan, no less than by numerous
valleys and clefts, and they are 436 miles apart.
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