cular hollows formed in the plain of Rosarno.]

A small circular pond of similar character was formed not far from
Polistena (see fig. 83); and in the vicinity of Seminara, a lake was
suddenly caused by the opening of a great chasm, from the bottom of
which water issued. This lake was called Lago del Tolfilo. It extended
1785 feet in length, by 937 in breadth, and 52 in depth. The
inhabitants, dreading the miasma of this stagnant pool, endeavored, at
great cost, to drain it by canals, but without success, as it was fed by
springs issuing from the bottom of the deep chasm.

Vivenzio states, that near Sitizzano a valley was nearly filled up to a
level with the high grounds on each side, by the enormous masses
detached from the boundary hills, and cast down into the course of two
streams. By this barrier a lake was formed of great depth, about two
miles long and a mile broad. The same author mentions that, upon the
whole, there were fifty lakes occasioned during the convulsions: and he
assigns localities to all of these. The government surveyors enumerated
215 lakes; but they included in this number many small ponds.

[Illustration: Fig. 83.

Circular pond near Polistena, in Calabria, caused by the earthquake in
1783.]

_Cones of sand thrown up._--Many of the appearances exhibited in the
alluvial plains, such as springs spouting up their water like fountains
at the moment of the shock, have been supposed to indicate the alternate
rising and sinking of the ground. The first effect of the more violent
shocks was usually to dry up the rivers, but they immediately afterwards
overflowed their banks. In marshy places, an immense number of cones of
sand were thrown up. These appearances Hamilton explains, by supposing
that the first movement raised the fissured plain from below upwards, so
that the rivers and stagnant waters in bogs sank down, or at least were
not upraised with the soil. But when the ground returned with violence
to its former position, the water was thrown up in jets through
fissures.[671]

The phenomenon, according to Mr. Mallet, may be simply an accident
contingent on the principal cause of disturbance, the rapid transit of
the earth-wave. "The sources," he says, "of copious springs usually lie
in flat plates or fissures filled with water, whether issuing from solid
rock, or from loose materials; now, if a vein, or thin flat cavity
filled with water, be in such a position that the plane of the plate of